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11.2: Using Other Software as Building Blocks

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    Software today is often quite complex. So complex that it is nearly impossible for one organization to write all the code. Frequently developers will use smaller pieces of code as building blocks. For example, imagine a developer making an application similar to Spotify. There could be a fair amount of custom code such as user account management, storing and retrieving playlists or songs, etc... The code to take an audio file and convert it to sound is fairly low level and would have to support edge cases such as older file formats (.WAV files), support digital rights management and decompress the audio. In this case, the developer may choose to use a "library" or "package" which manages these tasks. Such a library would handle the mundane tasks such as converting the file to audio, obtaining track metadata such as title and artist from the file and similar functions.

    Using these libraries has some benefits including:

    • Libraries are often used by multiple software and are generally tested more robustly than standalone code

    • Libraries preclude developers from having to deal with edge cases or areas of concern which reside outside the comfort of the developer

    • Popular libraries tend to have a good community following, so help is often easy to come by

    Be aware that libraries can have some downsides as well.

    Supply Chain Attacks

    A "supply chain attack" occurs when someone knowingly supplies something with malintent in an effort to disrupt, observe or destroy a consumer upstream.

    The Restaurant

    Consider the case where a head chef, Addison, is expecting a food critic (Blair) at Addison's new restaurant. Sous Chef (Charlie) is jealous of Addison and knows that a bad review might end Addison's career. Charlie devises a plan: when Addison asks for sugar to make candied sauce for the vegetables, Charlie will hand Addison the salt instead.

    This is a "supply chain attack" because Charlie knowingly supplies the wrong ingredient to Addison. Addison may not even realize this because the salt looks and feels like sugar. When the critic tastes the candied vegetables and realizes that they taste terrible instead of sweet, Addison will get a bad review.

    In software, particularly web applications, this attack can be devastating. Most web applications these days rely on tens, hundreds or thousands of small libraries. The "NPM" packages (NPM stands for Node Package Manager) libraries - often implemented in JavaScript - are suitable both for front-end applications as well as back-end logic.

    The Case of "left-pad"

    In 2016, a developer removed a very small piece of code from NPM2. The code was called "left-pad" and was less than 12 lines long. The package merely added spaces to the left part of a string in order to make the string a specific length. For example, this code:

    leftpad("hello", 10)

    Would return the string "     hello" (note that the string is now 10 characters long). While this code is not complicated, it is quite useful (often used for aligning text). As such, it was used by thousands of packages. And those packages, in turn, were used by thousands more packages. All of a sudden, hundreds of thousands developers noticed that their code would not compile because left-pad was no longer found.

    The developer who removed the code likely did not anticipate the scope of the problem; in response, NPM published the package again and also removed the ability for developers to delete a package under normal circumstances.

    While the removal of left-pad was not intended to cause problems around the globe, it was a high profile example of just how fragile library supply chains can be.


    The Russian incursion of Ukraine in March 2022 has led to the emergence of protestware - that is, intentional poisoning of a supply chain. The first known occurrence happened in mid-March. An NPM package called node-ipc was updated to remove files from the user’s machine and replace them with an emoji of a heart (assuming the computer was geolocated in Russia or Belarus)3.


    Crime can pay! In 2021, a security research firm identified several NPM packages which secretly installed crypto mining4 software on developers machines.

    This example is more common; that is, packages which intend to be malicious. Sometimes malware may be included in packages in order to steal credentials, compromise developers computers or initiate a ransomware campaign.

    Video Players

    In January 2022 Palo Alto Networks Unit 42 discovered a dangerous (and admirable!) supply-chain attack on cloud-based, customizable JavaScript video players mostly used on real estate sites. The attackers were able to access the upstream JavaScript file and include malicious skimming code. “On the next player update, the video player began 

    serving the malicious script to all sites that already had the player embedded5”. The attackers were able to abscond with names, addresses, phone numbers, and credit card information.

    Okta Attack

    You may never have heard of Okta before, but they are an authentication firm with 15,000 clients (including FedEx and CloudFlare) so there is a good chance you use some of their services in some capacity. In January 2022, an account take over (ATO) at one of Okta’s service providers led to downstream effects including affects for 366 of Okta’s clients6. This is an especially interesting case of a supply chain attack in that Okta itself is a supply chain target but their reliance on Sitel as a third-party provider resulted in the attack. It was a supply chain attack on a supply chain provider.

    Whereas a supply chain attack might be characterized as “getting the keys to the kingdom”, attacking Okta and other similar providers is more like “getting keys to the factory where the keys to multiple kingdoms are made”.

    Combating Supply Chain Attacks

    Supply chain attacks happen all the time (MailChimp in 20227, Microsoft Exchange Server in 20218, SolarWinds in 20209, British Airways in 201810) but there are ways to mitigate them. While some might argue that building systems from scratch instead of relying on code reuse is the solution, the adage “Given enough eyeballs all bugs are shallow11” is a potent reminder of the durability of well-vetted open-source software. One particular weakness of a home-grown solution is that the code is private and cannot be audited. For a recent example look no further than Samsung’s proprietary implementation of Android’s Trusted Execution Environment that led to vulnerabilities in 100 million smartphones12. Or consider a (as of this writing) still persistent mishandling of account logins at Coinbase - bad actors can gain intelligence on email accounts linked to a Coinbase account, easing phishing campaigns. The issue is that a bad actor can divine email addresses with a Coinbase account and then target them. This isn’t the first time Coinbase suffered from a vulnerable design. In 2019 a data exposure revealed 3,500 plaintext passwords13 and in 2021 over 6,000 accounts had cryptocurrency stolen because of a flaw in the SMS account recover scheme14. While there is no evidence to support the claim that the email confirmation/denial issue is a byproduct of homegrown code, that type of mistake is indicative of amateur programming.

    We have started to see attempts at securing supply chain attacks. In May 2021, Executive Order 14028 Improving the nation’s cybersecurity was given. In response, in July 2021 the National Institute of Standards and Technology (NIST), along with the Cybersecurity & Infrastructure Security Agency (CISA) and the Office of Management and Budget (OMB) released two key publications15 that are stage three of a seven stop program:

    Outside of governmental involvement there are a few different private endeavors that are being rolled out. Described in more detail in the next section, GitHub’s Dependabot helps by alerting developers of supply chain threats16. Additionally, Google is creating tools and methodology to help developers verify “build provenance”. In other words, developers can be equipped with tools that will help verify that source files are not malicious or that malicious artifacts have not been injected into code. The framework that improves the integrity of development is known as Supply-chain Levels for Software Artifacts (SLSA)17. As supply chain attacks increase, tools to help combat them will also increase in efficacy and adoption.

    TechRadar ran a piece in March 2022 suggesting that developers accept that fact that code reuse is inevitable so proper mechanisms to verify the code in development and distribution is a proactive way to mitigate supply chain attacks18.

    Vulnerable and Outdated Components

    Using libraries, packages or components from third parties can introduce security concerns. OWASP lists this as number 6 on their top 10 list19. Generally this refers to software libraries which either contain security vulnerabilities (inadvertently) or become outdated.


    Just in time for Christmas in 2021, the very popular library log4j was discovered to have a remote code execution vulnerability20. The vulnerability had existed for years and affected several versions of the software. When news of this vulnerability surfaced, companies around the world had to fix or update their code in order to ensure that they were not vulnerable.


    The openssl library might be considered the de-facto standard for open source encryption. Providing services such as encryption, decryptions and certificate validation, it is important in nearly all manners of encryption. While it is expected that vulnerabilities exist in all software, some particularly nasty bug were found in 2003 which led to the ability to trick servers into disclosing the server's private key21.

    The way to mitigate such an attack is to keep libraries up to date. This can be an automated process. For example, GitHub provides the use of "dependabot22", which was originally released in 2020 as a way to automate dependencies with security issues23, the most recent version released in April 2022 notifies software authors when libraries are available which address vulnerabilities24. The dependabot can also offer to patch software with the latest version.


    Even software as innocuous as compression software can be problematic. In 2019, researchers found an error with WinRAR that let attackers gain full control over a user’s computer25! Issues like this can be especially insidious because users have an implicit belief that popular utilities should be relatively safe (and for 19 years, WinRAR was safe). But the most pernicious part of this story is that WinRAR does not have an automatic update feature - so unless everyday users get their daily news from cybersecurity outlets, there is a good chance people are unaware of the issue (or that the issue can be fixed with a simple update). 


    We see the no-automatic-updates problem often in home routers as well. Though the latest trend in home routers do a much better job of updating automatically, for a long time that was not the case. And the percentage of average users that ventured into their router to manually check for updates and install any updates that exist is probably very low. This problem is even worse when companies are aware that their products are susceptible to attacks and won’t even release updates. This happened in late 2021 when Cisco informed users of remote attack that gave unauthenticated attackers the ability to execute arbitrary code on the target device26.

    Dependency Confusion

    Another fascinating attack was discovered by ethical hacker Alex Birsan in February 2021 (he reportedly made roughly $130,00 in bug bounties for this discovery). Dubbed dependency confusion, the hack was simple. In fact, it did not even require malicious injections; rather his hack leveraged poor design for software development processes. The oversimplified explanation is simple27:

    • Companies have private code repositories that other code relies on

    • Birsan found those repository names in code that was published

    • Birsan then publicly published his own code with the same repository name

    • Companies’ development tools defaulted to the public repository when given the option

    • Birsan pwned many companies including Apply, Microsoft, and Shopify

    As a reminder to cybersecurity professionals - when a vulnerability is published, fix any liabilities in your organization. In the wake of Birsan’s post, copycats of his attack targeted several companies (including Amazon, Slack, Zillow, and Lyft) by poisoning public repos that were relied on28.

    But this isn’t the only threat based on a model of developing using repositories. A similar attack, repo jacking, requires more malicious energy. If an attacker knows what GitHub repositories a company relies on, that hacker can monitor the dependent repositories. If the owner of the repository changes their username, the hacker can swoop in, create an account with that username, and then publish their own code29.


    1. How one programmer broke the internet by deleting a tiny piece of code
    2. Sabotage: Code added to popular NPM package wiped files in Russia and Belarus
    3. Popular npm Project Used by Millions Hijacked in Supply-Chain Attack
    4. Hackers use video player to steal credit cards from over 100 sites
    5. Okta Says It Goofed in Handling the Lapsus$ Attack
    6. Mailchimp hacked to launch ‘exceptional’ supply chain attack
    7. China’s and Russia’s spying sprees will take years to unpack
    8. What You Need to Know About the SolarWinds Supply-Chain Attack
    9. British Airways breach: How did hackers get in?
    10. Linus's law [Wikipedia]
    11. 100 million Samsung phones affected by encryption weakness
    12. Coinbase Hack Attributed to a Multi-factor Authentication Flaw That Allowed Scammers To Steal Cryptocurrency
    13. Coinbase says hackers stole cryptocurrency from at least 6,000 customers
    14. NIST Delivers Two Key Publications to Enhance Software Supply Chain Security Called for by Executive Order
    15. Secure your software supply chain
    16. Improving software supply chain security with tamper-proof builds
    17. How to finally secure the software supply chain
    18. A06:2021 – Vulnerable and Outdated Components
    19. Log4j Vulnerability FAQs
    20. Debian Security Advisory
    21. GitHub dependabot
    22. Keep all your packages up to date with Dependabot
    23. Prevent the introduction of known vulnerabilities into your code
    24. Extracting a 19 Year Old Code Execution from WinRAR
    25. Cisco Small Business routers vulnerable to remote attacks, won’t get a patch
    26. Dependency Confusion: How I Hacked Into Apple, Microsoft and Dozens of Other Companies
    27. Malicious NPM packages target Amazon, Slack with new dependency attacks
    28. Repo Jacking: Exploiting the Dependency Supply Chain

    11.2: Using Other Software as Building Blocks is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

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