The days of open outcry on trading floors of the NYSE, NASDAQ, and other stock exchanges around the globe are gone. With the advent of electronic trading platforms and networks, the exchange of financial securities now is easier and faster than ever; but this comes with inherent risks.
Are You Trading Stocks Securely? Exposing Security Flaws in Trading Technologies
By
Alejandro Hernandez
This blog post contains a small portion of the entire analysis. Please refer to the white paper for full details to the research.
Disclaimer
Most of the testing was performed using paper money (demo accounts) provided online by the brokerage houses. Only a few accounts were funded with real money for testing purposes. In the case of commercial platforms, the free trials provided by the brokers were used. Only end-user applications and their direct servers were analyzed. Other backend protocols and related technologies used in exchanges and financial institutions were not tested.
This research is not about High Frequency Trading (HFT), blockchain, or how to get rich overnight.
Introduction
The days of open outcry on trading floors of the NYSE, NASDAQ, and other stock exchanges around the globe are gone. With the advent of electronic trading platforms and networks, the exchange of financial securities now is easier and faster than ever; but this comes with inherent risks.
The valuable information as well as the attack surface and vectors in trading environments are slightly different than those in banking systems.
Brokerage houses offer trading platforms to operate in the market. These applications allow you to do things including, but not limited to:
Fund your account via bank transfers or credit card
Keep track of your available equity and buying power (cash and margin balances)
Monitor your positions (securities you own) and their performance (profit)
Monitor instruments or indexes
Send buy/sell orders
Create alerts or triggers to be executed when certain thresholds are reached
Receive real-time news or video broadcasts
Stay in touch with the trading community through social media and chats
Needless to say, every single item on the previous list must be kept secret and only known by and shown to its owner.
Scope
My analysis started mid-2017 and concluded in July 2018. It encompassed the following platforms; many of them are some of the most used and well-known trading platforms, and some allow cryptocurrency trading:
16 Desktop applications
34 Mobile apps
30 Websites
These platforms are part of the trading solutions provided by the following brokers, which are used by tens of millions of traders. Some brokers offer the three types of platforms, however, in some cases only one or two were reviewed due to certain limitations:
Ally Financial
AvaTrade
Binance
Bitfinex
Bitso
Bittrex
Bloomberg
Capital One
Charles Schwab
Coinbase
easyMarkets
eSignal
ETNA
eToro
E-TRADE
ETX Capital
ExpertOption
Fidelity
Firstrade
FxPro
GBMhomebroker
Grupo BMV
IC Markets
Interactive Brokers
IQ Option
Kraken
com
Merrill Edge
MetaTrader
Net
NinjaTrader
OANDA
Personal Capital
Plus500
Poloniex
Robinhood
Scottrade
TD Ameritrade
TradeStation
Yahoo! Finance
Devices used:
Windows 7 (64-bit)
Windows 10 Home Single (64-bit)
iOS 10.3.3 (iPhone 6) [not jailbroken]
iOS 10.4 (iPhone 6) [not jailbroken]
Android 7.1.1 (Emulator) [rooted]
Basic security controls/features were reviewed that represent just the tip of the iceberg when compared to more exhaustive lists of security checks per platform.
Results
Unfortunately, the results proved to be much worse compared with applications in retail banking. For example, mobile apps for trading are less secure than the personal banking apps reviewed in 2013 and 2015.
Apparently, cybersecurity has not been on the radar of the Financial Services Tech space in charge of developing trading apps. Security researchers have disregarded these technologies as well, probably because of a lack of understanding of money markets.
While testing I noted a basic correlation: the biggest brokers are the ones that invest more in fintech cybersecurity. Their products are more mature in terms of functionality, usability, and security.
Based on my testing results and opinion, the following trading platforms are the most secure:
Broker
Platforms
TD Ameritrade
Web and mobile
Charles Schwab
Web and mobile
Merrill Edge
Web and mobile
MetaTrader 4/5
Desktop and mobile
Yahoo! Finance
Web and mobile
Robinhood
Web and mobile
Bloomberg
Mobile
TradeStation
Mobile
Capital One
Mobile
FxPro cTrader
Desktop
IC Markets cTrader
Desktop
Ally Financial
Web
Personal Capital
Web
Bitfinex
Web and mobile
Coinbase
Web and mobile
Bitso
Web and mobile
The medium- to high-risk vulnerabilities found on the different platforms include full or partial problems with encryption, Denial of Service, authentication, and/or session management problems. Despite the fact that these platforms implement good security features, they also have areas that should be addressed to improve their security.
Following the platforms I consider must improve in terms of security:
Broker
Platforms
Interactive Brokers
Desktop, web and mobile
IQ Option
Desktop, web and mobile
AvaTrade
Desktop and mobile
E-TRADE
Web and mobile
eSignal
Desktop
TD Ameritrade’s Thinkorwim
Desktop
Charles Schwab
Desktop
TradeStation
Desktop
NinjaTrader
Desktop
Fidelity
Web
Firstrade
Web
Plus500
Web
Markets.com
Mobile
Unencrypted Communications
In 9 desktop applications (64%) and in 2 mobile apps (6%), transmitted data unencrypted was observed. Most applications transmit most of the sensitive data in an encrypted way, however, there were some cases where cleartext data could be seen in unencrypted requests.
Among the data seen unencrypted are passwords, balances, portfolio, personal information and other trading-related data. In most cases of unencrypted transmissions, HTTP in plaintext was seen, and in others, old proprietary protocols or other financial protocols such as FIX were used.
Under certain circumstances, an attacker with access to some part of the network, such as the router in a public WiFi, could see and modify information transmitted to and from the trading application. In the trading context, a malicious actor could intercept and alter values, such as the bid or ask prices of an instrument, and cause a user to buy or sell securities based on misleading information.
For example, the follow application uses unencrypted HTTP. In the screenshot, a buy order:
Another interesting example was found in eSignal’s Data Manager. eSignal is a known signal provider and integrates with a wide variety of trading platforms. It acts as a source of market data. During the testing, it was noted that Data Manager authenticates over an unencrypted protocol on the TCP port 2189, apparently developed in 1999.
As can be seen, the copyright states it was developed in 1999 by Data Broadcasting Corporation. Doing a quick search, we found a document from the SEC that states the company changed its name to Interactive Data Corporation, the owners of eSignal. In other words, it looks like it is an in-house development created almost 20 years ago. We could not corroborate this information, though.
The main eSignal login screen also authenticates through a cleartext channel:
FIX is a protocol initiated in 1992 and is one of the industry standard protocols for messaging and trade execution. Currently, it is used by a majority of exchanges and traders. There are guidelines on how to implement it through a secure channel, however, the binary version in cleartext was mostly seen. Tests against the protocol itself were not performed in this analysis.
A broker that supports FIX:
There are some cases where the application encrypts the communication channel, except in certain features. For instance, Interactive Brokers desktop and mobile applications encrypt all the communication, but not that used by iBot, the robot assistant that receives text or voice commands, which sends the instructions to the server embedded in a FIX protocol message in cleartext:
News related to the positions were also observed in plaintext:
Another instance of an application that uses encryption but not for certain channels is this one, Interactive Brokers for Android, where a diagnostics log with sensitive data is sent to the server in a scheduled basis through unencrypted HTTP:
A similar platform that sends everything over HTTPS is IQ Option, but for some reason, it sends duplicate unencrypted HTTP requests to the server disclosing the session cookie.
Others appear to implement their own binary protocols, such as Charles Schwab, however, symbols in watchlists or quoted symbols could be seen in cleartext:
Interactive Brokers supports encryption but by default uses an insecure channel; an inexperienced user who does not know the meaning of “SSL” (Secure Socket Layer) won’t enable it on the login screen and some sensitive data will be sent and received without encryption:
Passwords Stored Unencrypted
In 7 mobile apps (21%) and in 3 desktop applications (21%), the user’s password was stored unencrypted in a configuration file or sent to log files. Local access to the computer or mobile device is required to extract them, though. This access could be either physical or through malware.
In a hypothetical attack scenario, a malicious user could extract a password from the file system or the logging functionality without any in-depth know-how (it’s relatively easily), log in through the web-based trading platform from the brokerage firm, and perform unauthorized actions. They could sell stocks, transfer the money to a newly added bank account, and delete this bank account after the transfer is complete. During testing, I noticed that most web platforms (+75%) support two-factor authentication (2FA), however, it’s not enabled by default, the user must go to the configuration and enable it to receive authorization codes by text messages or email. Hence, if 2FA is not enabled in the account, it’s possible for an attacker, that knows the password already, to link a new bank account and withdraw the money from sold securities.
The following are some instances where passwords are stored locally unencrypted or sent to logs in cleartext:
Base64 is not encryption:
In some cases, the password was sent to the server as a GET parameter, which is also insecure:
One PIN for login and unlocking the app was also seen:
In IQ Option, the password was stored completely unencrypted:
However, in a newer version, the password is encrypted in a configuration file, but is still stored in cleartext in a different file:
Trading and Account Information Stored Unencrypted
In the trading context, operational or strategic data must not be stored unencrypted nor sent to the any log file in cleartext. This sensitive data encompasses values such as personal data, general balances, cash balance, margin balance, net worth, net liquidity, the number of positions, recently quoted symbols, watchlists, buy/sell orders, alerts, equity, buying power, and deposits. Additionally, sensitive technical values such as username, password, session ID, URLs, and cryptographic tokens should not be exposed either.
8 desktop applications (57%) and 15 mobile apps (44%) sent sensitive data in cleartext to log files or stored it unencrypted. Local access to the computer or mobile device is required to extract this data, though. This access could be either physical or through malware.
If these values are somehow leaked, a malicious user could gain insight into users’ net worth and investing strategy by knowing which instruments users have been looking for recently, as well as their balances, positions, watchlists, buying power, etc.
The following screenshots show applications that store sensitive data unencrypted:
Balances:
Investment portfolio:
Buy/sell orders:
Watchlists:
Recently quoted symbols:
Other data:
Trading Programming Languages with DLL Import Capabilities
This is not a bug, it’s a feature. Some trading platforms allow their customers to create their own automated trading robots (a.k.a. expert advisors), indicators, and other plugins. This is achieved through their own programming languages, which in turn are based on other languages, such as C++, C#, or Pascal.
The following are a few of the trading platforms with their own trading language:
MetaTrader: MetaQuotes Language (Based on C++ – Supports DLL imports)
NinjaTrader: NinjaScript (Based on C# – Supports DLL imports)
TradeStation: EasyLanguage (Based on Pascal – Supports DLL imports)
AvaTraceAct: ActFX (Based on Pascal – Does not support OS commands nor DLL imports)
(FxPro/IC Markets) cTrader: Based on C# (OS command and DLL support is unknown)
Nevertheless, some platforms such as MetaTrader warn their customers about the dangers related to DLL imports and advise them to only execute plugins from trusted sources. However, there are Internet tutorials claiming, “to make you rich overnight” with certain trading robots they provide. These tutorials also give detailed instructions on how to install them in MetaTrader, including enabling the checkbox to allow DLL imports. Innocent non-tech savvy traders are likely to enable such controls, since not everyone knows what a DLL file is or what is being imported from it. Dangerous.
Following a malicious Ichimoku indicator that, when loaded into any chart, downloads and executes a backdoor for remote access:
Another basic example is NinjaTrader, which simply allows OS commands through C#’s System.Diagnostics.Process.Start(). In the following screenshot, calc.exe executed from the chart initialization routine:
Denial of Service
Many desktop platforms integrate with other trading software through common TCP/IP sockets. Nevertheless, some common weaknesses are present in the connections handling of such services.
A common error is not implementing a limit of the number of concurrent connections. If there is no limit of concurrent connections on a TCP daemon, applications are susceptible to denial-of-service (DoS) or other type of attacks depending on the nature of the applications.
For example, TD Ameritrade’s Thinkorswim TCP-Orders Server listens on the TCP port 2000 in the localhost interface, and there is no limit for connections nor a waiting time between orders. This leads to the following problems:
Memory leakage since, apparently, the resources assigned to every connection are not freed upon termination.
Continuous order pop-ups (one pop-up per order received through the TCP server) render the application useless.
A NULL pointer dereference is triggered and an error report (.zip file) is created.
Regardless, it listens on the local interface only. There are different ways to reach this port, such as XMLHttpRequest() in JavaScript through a web browser.
Memory leakage could be easily triggered by creating as many connections as possible:
A similar DoS vulnerability due to memory exhaustion was found in eSignal’s Data Manager. eSignal is a known signal provider and integrates with a wide variety of trading platforms. It acts as a source of market data; therefore, availability is the most important asset:
It’s recommended to implement a configuration item to allow the user to control the behavior of the TCP order server, such as controlling the maximum number of orders sent per minute as well as the number of seconds to wait between orders to avoid bottlenecks.
The following capture from Interactive Brokers shows when this countermeasure is implemented properly. No more than 51 users can be connected simultaneously:
Session Still Valid After Logout
Normally, when the logout button is pressed in an app, the session is finished on both sides: server and client. Usually the server deletes the session token from its valid session list and sends a new empty or random value back to the client to clear or overwrite the session token, so the client needs to reauthenticate next time.
In some web platforms such as E-TRADE, Charles Schwab, Fidelity and Yahoo! Finance (Fixed), the session was still valid one hour after clicking the logout button:
Authentication
While most web-based trading platforms support 2FA (+75%), most desktop applications do not implement it to authenticate their users, even when the web-based platform from the same broker supports it.
Nowadays, most modern smartphones support fingerprint-reading, and most trading apps use it to authenticate their customers. Only 8 apps (24%) do not implement this feature.
Unfortunately, using the fingerprint database in the phone has a downside:
Weak Password Policies
Some institutions let the users choose easily guessable passwords. For example:
The lack of a secure password policy increases the chances that a brute-force attack will succeed in compromising user accounts.
In some cases, such as in IQ Option and Markets.com, the password policy validation is implemented on the client-side only, hence, it is possible to intercept a request and send a weak password to the server:
Automatic Logout/Lockout for Idle Sessions
Most web-based platforms logout/lockout the user automatically, but this is not the case for desktop (43%) and mobile apps (25%). This is a security control that forces the user to authenticate again after a period of idle time.
Privacy Mode
This mode protects the customers’ private information from being displayed on the screen in public areas where shoulder-surfing attacks are feasible. Most of the mobile apps, desktop applications, and web platforms do not implement this useful and important feature.
The following images show before and after enabling privacy mode in Thinkorswim for mobile:
Hardcoded Secrets in Code and App Obfuscation
16 Android .apk installers (47%) were easily reverse engineered to human-readable code since they lack of obfuscation. Most Java and .NET-based desktop applications were also reverse-engineered easily. The rest of the applications had medium to high levels of obfuscation, such as Merrill Edge in the next screenshot.
The goal of obfuscation is to conceal the applications purpose (security through obscurity) and logic in order to deter reverse engineering and to make it more difficult.
In the non-obfuscated platforms, there are hardcoded secrets such as cryptographic keys and third-party service partner passwords. This information could allow unauthorized access to other systems that are not under the control of the brokerage houses. For example, a Morningstar.com account (investment research) hardcoded in a Java class:
Interestingly, 14 of the mobile apps (41%) and 4 of the desktop platforms (29%) have traces (hostnames and IPs) about the internal development and testing environments where they were made or tested. Some hostnames are reachable from the Internet and since they’re testing systems they could lack of proper protections.
SSL Certificate Validation
11 of the reviewed mobile apps (32%) do not check the authenticity of the remote endpoint by verifying its SSL certificate; therefore, it’s feasible to perform Man-in-the-Middle (MiTM) attacks to eavesdrop on and tamper with data. Some MiTM attacks require to trick the user into installing a malicious certificate on their phones, though.
The ones that verify the certificate normally do not transmit any data, however, only Charles Schwab allows the user to use the app with the provided certificate:
Lack of Anti-exploitation Mitigations
ASLR randomizes the virtual address space locations of dynamically loaded libraries. DEP disallows the execution of data in the data segment. Stack Canaries are used to identify if the stack has been corrupted. These security features make much more difficult for memory corruption bugs to be exploited and execute arbitrary code.
The majority of the desktop applications do not have these security features enabled in their final releases. In some cases, that these features are only enabled in some components, not the entire application. In other cases, components that handle network connections also lack these flags.
Linux applications have similar protections. IQ Option for Linux does not enforce all of them on certain binaries.
Other Weaknesses
More issues were found in the platforms. For more details, please refer to the white paper.
Statistics
Since a picture is worth a thousand words, consider the following graphs:
For more statistics, please refer to the white paper.
Responsible Disclosure
One of IOActive’s missions is to act responsibly when it comes to vulnerability disclosure. In September 2017 we sent a detailed report to 13 of the brokerage firms whose mobile trading apps presented some of the higher risks vulnerabilities discussed in this paper. More recently, between May and July 2018, we sent additional vulnerability reports to brokerage firms.
As of July 27, 2018, 19 brokers that have medium- or high-risk vulnerabilities in any of their platforms were contacted.
TD Ameritrade and Charles Schwab were the brokers that communicated more with IOActive for resolving the reported issues.
For a table with the current status of the responsible disclosure process, please refer to the white paper.
Conclusions and Recommendations
Trading platforms are less secure than the applications seen in retail banking.
There’s still a long way to go to improve the maturity level of security in trading technologies.
End users should enable all the security mechanisms their platforms offer, such as 2FA and/or biometric authentication and automatic lockout/logout. Also, it’s recommended not to trade while connected to public networks and not to use the same password for other financial services.
Brokerage firms should perform regular internal audits to continuously improve the security of their trading platforms.
Brokerage firms should also offer security guidance in their online education centers.
Developers should analyze their current applications to determine if they suffer from the vulnerabilities described in this paper, and if so, fix them.
Developers should design new, more secure financial software following secure coding practices.
Regulators should encourage brokers to implement safeguards for a better trading environment. They could also create trading-specific guidelines to be followed by the brokerage firms and FinTech companies in charge of creating trading software.
Rating organizations should include security in their reviews.
Side Note
Remember: the stock market is not a casino where you magically get rich overnight. If you lack an understanding of how stocks or other financial instruments work, there is a high risk of losing money quickly. You must understand the market and its purpose before investing.
With nothing left to say, I wish you happy and secure trading!
Security Theater and the Watch Effect in Third-party Assessments
By
Daniel Miessler
Before the facts were in, nearly every journalist and salesperson in infosec was thinking about how to squeeze lemonade from the Equifax breach. Let’s be honest – it was and is a big breach. There are lessons to be learned, but people seemed to have the answers before the facts were available.
It takes time to dissect these situations and early speculation is often wrong. Efforts at attribution and methods take months to understand. So, it’s important to not buy into the hysteria and, instead, seek to gain a clear vision of the actual lessons to be learned. Time and again, these supposed “watershed moments” and “wake-up calls” generate a lot of buzz, but often little long-term effective action to improve operational resilience against cyber threats.
At IOActive we guard against making on-the-spot assumptions. We consider and analyze the actual threats, ever mindful of the “Watch Effect.” The Watch Effect can be simply explained: you wear a watch long enough, you can’t even feel it.
I won’t go into what third-party assessments Equifax may or may not have had because that’s largely speculation. The company has probably been assessed many times, by many groups with extensive experience in the prevention of cyber threats and the implementation of active defense. And they still experienced a deep impact cyber incursion.
The industry-wide point here is: Everyone is asking everyone else for proof that they’re secure.
The assumption and Watch Effect come in at the point where company executives think their responses to high-level security questions actually mean something.
Well, sure, they do mean something. In the case of questionnaires, you are asking a company to perform a massive amount of tedious work, and, if they respond with those questions filled in, and they don’t make gross errors or say “no” where they should have said “yes”, that probably counts for something.
But the question is how much do we really know about a company’s security by looking at their responses to a security questionnaire?
The answer is, “not much.”
As a company that has been security testing for 20 years now, IOActive has successfully breached even the most advanced cyber defenses across countless companies during penetration tests that were certified backwards and forwards by every group you can imagine. So, the question to ask is, “Do questionnaires help at all? And if so, how much?”
Here’s a way to think about that.
At IOActive we conduct full, top-down security reviews of companies that include business risk, crown-jewel defense, and every layer that these pieces touch. Because we know how attackers get in, we measure and test how effective the company is at detecting and responding to cyber events – and use this comprehensive approach to help companies understand how to improve their ability to prevent, detect, and ever so critically, RESPOND to intrusions. Part of that approach includes a series of interviews with everyone from the C-suite to the people watching logs. What we find is frightening.
We are often days or weeks into an assessment before we discover a thread to pull that uncovers a major risk, whether that thread comes from a technical assessment or a person-to-person interview or both.
That’s days—or weeks—of being onsite with full access to the company as an insider.
Here’s where the Watch Effect comes in. Many of the companies have no idea what we’re uncovering or how bad it is because of the Watch Effect. They’re giving us mostly standard answers about their day-to-day, the controls they have in place, etc. It’s not until we pull the thread and start probing technically – as an attacker – that they realize they’re wearing a broken watch.
Then they look down at a set of catastrophic vulnerabilities on their wrist and say, “Oh. That’s a problem.”
So, back to the questionnaire…
If it takes days or weeks for an elite security firm to uncover these vulnerabilities onsite with full cooperation during an INTERNAL assessment, how do you expect to uncover those issues with a form?
You can’t. And you should stop pretending you can. Questionnaires depend far too much upon the capability and knowledge of the person or team filling it out, and often are completed with impartial knowledge. How would one know if a firewall rule were updated improperly to “any/any” in the last week if it is not tested and verified?
To be clear, the problem isn’t that third party assessments only give 2/10 in security assessment value. The problem is that executives THINK it’s giving them 6/10, or 9/10.
It’s that disconnect that’s causing the harm.
Eventually, companies will figure this out. In the meantime, the breaches won’t stop.
Until then, we as technical practitioners can do our best to convince our clients and prospects to understand the value these types of cursory, external glances at a company provide. Very little. So, let’s prioritize appropriately.
Two years ago, I decided to conduct research in order to obtain a global view of the state of security of mobile banking apps from some important banks. In this blog post, I will present my latest results to show how the security of the same mobile banking apps has evolved.
Sometimes when buying something that costs $0.99 USD (99 cents) or $1.01 USD (one dollar and one cent), you may pay an even dollar. Either you or the cashier may not care about the remaining penny, and so one of you takes a small loss or profit.
Rounding at the cash register is a common practice, just as it is in programming languages when dealing with very small or very large numbers. I will describe here how an attacker can make a profit when dealing with the rounding mechanisms of programming languages.
Lack of precision in numbers
IEEE 754 standard has defined floating point numbers for more than 30 years. The requirements that guided the formulation of the standard for binary floating-point arithmetic provided for the development of very high-precision arithmetic.
The standard defines how operations with floating point numbers should be performed, and also defines standard behavior for abnormal operations. It identifies five possible types of floating point exceptions: invalid operation (highest priority), division by zero, overflow, underflow, and inexact (lowest priority).
We will explore what happens when inexact floating point exceptions are triggered. The rounded result of a valid operation can be different from the real (and sometimes infinitely precise) result and certain operations may go unnoticed.
Rounding
Rounding takes an exact number and, if necessary, modifies it to fit in the destination’s format. Normally, programming languages do not alert for the inexact exception and instead just deliver the rounded value. Nevertheless, documentation for programming languages contains some warnings about this:
Ruby clearly states that floating point has a different arithmetic and is a inexact number.
To exemplify this matter, this is how the number 0.1 looks internally in Python:
The decimal value 0.1 cannot be represented precisely when using binary notation, since it is an infinite number in base 2. Python will round the previous number to 0.1 before showing the value.
Salami slicing the decimals
Salami slicing refers to a series of small actions that will produce a result that would be impossible to perform all at once. In this case, we will grab the smallest amount of decimals that are being ignored by the programming language and use that for profit.
Let’s start to grab some decimals in a way that goes unnoticed by the programming language. Certain calculations will trigger more obvious differences using certain specific values. For example, notice what happens when using v8 (Google’s open source JavaScript engine) to add the values 0.1 plus 0.2:
Perhaps we could take some of those decimals without JavaScript noticing:
But what happens if we are greedy? How much can we take without JavaScript noticing?
That’s interesting; we learned that it is even possible to take more than what was shown, but no more than 0.00000000000000008 from that operation before JavaScript notices.
I created a sample bank application to explain this, pennies.js:
// This is used to wire money
function wire(deposit, money, withdraw) {
account[deposit] += money;
account[withdraw] -= money;
if(account[withdraw]<0)
return 1; // Error! The account can not have a negative balance
for(i = 0.000000000000000001; i < 0.1; i+=0.0000000000000000001) {
reset_values();
wire(1, i, 0); // I will transfer some cents from the account 0 to the account 1
if(account[0]==initial_deposit && i>profit) {
profit = i;
// print(“I can grab “+profit.toPrecision(21));
} else {
break;
}
}
print(” Found: “+profit.toPrecision(21));
print(“n2) Let’s start moving some money:”);
reset_values();
start = new Date().getTime() / 1000;
for (j = 0; j < 10000000000; j++) {
for (i = 0; i < 1000000000; i++) {
wire(1, profit, 0); // I will transfer some cents from the account 0 to the account 1
}
finish = new Date().getTime() / 1000;
print_balance(finish-start);
}
The attack against it will have two phases. In the first phase, we will determine the maximum amount of decimals that we are allowed to take from an account before the language notices something is missing. This amount is related to the value from which we are we taking: the higher the value, the higher the amount of decimals. Our Bank Account 0 will have $1,000,000 USD to start with, and we will deposit our profits to a secondary Account 1:
Due to the decimals being silently shifted to Account 1, the bank now believes that it has more money than it actually has.
Another possibility to abuse the loss of precision is what happens when dealing with large numbers. The problem becomes visible when using at least 17 digits.
Now, the sample attack application will occur on a crypto currency, fakecoin.js:
// This is used to wire money
function wire(deposit, money, withdraw) {
account[deposit] += money;
account[withdraw] -= money;
if(account[withdraw]<0) {
return 1; // Error! The account can not have a negative balance
wire(1, j, 0); // I will transfer a few cents from the account 0 to the account 1
if(account[0]==initial_deposit && j > profit) {
profit = j;
} else {
break;
}
}
print(” Found: “+profit);
reset_values();
start = new Date().getTime() / 1000;
print(“n2) Let’s start moving some money”);
for (j = 0; j < 10000000000; j++) {
for (i = 0; i < 1000000000; i++) {
wire(1, profit, 0); // I will transfer my 29 cents from the account 0 to the account 1
}
finish = new Date().getTime() / 1000;
print_balance(finish-start);
}
We will buy 10000000000000000 units of Fakecoin (with each coin valued at $0.00000000011 USD) for a total value of $1,100,000 USD. We will transfer one Fakecoin at the time from Account 0 to a second account that will hold our profits (Account 1). JavaScript will not notice the missing Fakecoin from Account 0, and will allow us to profit a total of approximately $2,300 USD per day:
Depending on the implementation, a hacker can used either float numbers or large numbers to generate money out of thin air.
Conclusion
In conclusion, programmers can avoid inexact floating point exceptions with some best practices:
If you rely on values that use decimal numbers, use specialized variables like BigInteger in Java.
Do not allow values larger than 16 digits to be stored in variables and truncate decimals, or
Use libraries that rely on quadruple precision (that is, twice the amount of regular precision).
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