XSS Threat of CVE-2023-0107 in Memos

Introduction:

Imagine your favorite open source notepad app, the one you use for all your ideas and to-do lists. Now, picture a tiny bug hiding inside it, a bug that could turn your harmless notes into dangerous tools for bad guys. That's what happened in early 2023 with Memos, the popular markdown privacy-first, lightweight note-taking service, and a sneaky problem called CVE-2023-0107. This blog takes a detailed, yet accessible, look at the vulnerability that threatened to transform your simple notes into gateways for malicious actors, wielding the power of Cross-Site Scripting (XSS) attacks.

Unpacking the Vulnerability:

The story begins with Zlib, a compression library found in countless software applications. Versions prior to 1.2.12 had a hidden flaw in their decompression logic, a typo in the code if you will. This seemingly insignificant error, known as CVE-2023-0107, could be exploited by crafting specially formatted compressed data. Now, where does Memos come in? Unfortunately, versions prior to v0.10.0 relied on an outdated Zlib version, making them vulnerable to this nasty glitch.

The XSS Threat:

With CVE-2023-0107 in play, an attacker could unleash the power of XSS in Memos. Here's how the nightmare unfolds:

  1. Crafting the Malicious Note: The attacker creates a seemingly harmless markdown note containing text and embedded malicious javascript code.

  2. Triggering the XSS: When Memos processes the note, the vulnerable Zlib library unwittingly executes the embedded code, granting the attacker control over your browser session.

  3. Hijacking the Experience: With this newfound power, the attacker can have multiple vectors to exploit:

    • Taking Cookies: Picture cookies as small keys to your online accounts. The attacker might steal them, getting into your emails, social media, and even bank accounts.

    • Tricking People with Phishing: Users might be sent to fake login pages, giving away their important information without realizing it.

    • Messing with Notes: Think about someone adding harmful code to notes from other users, causing more trouble with XSS.

    • Remote Code Execution: In the worst situation, attackers could have complete control over users' systems by injecting code.

For the PoC, we will be using the following payload in our memos:
[a](javascript:window.onerror=alert`success`;throw%201)

Lessons Learned:

Thankfully, the Memos team acted swiftly, patching the vulnerability by upgrading Zlib to a secure version in v0.10.0 and adding extra input sanitization in their ReactJS code. The patch commit is accessible here. This effectively closed the XSS backdoor, restoring peace of mind to the markdown community. However, the incident serves as a stark reminder of several crucial lessons:

  • The Power of Updates: Regularly checking for and applying software updates, especially to libraries like Zlib, is crucial to staying ahead of vulnerabilities. Remember, an update today can prevent a nightmare tomorrow.

  • Security Hygiene Matters: Choosing well-maintained and secure software, employing strong passwords, and being wary of suspicious links are vital practices for digital safety. Think of it as digital hygiene, keeping your online world clean and protected.

  • Knowledge is Power: Understanding how vulnerabilities like XSS work empowers us to make informed decisions and protect ourselves from potential attacks. The more you know, the better equipped you are to navigate the digital landscape safely.

Beyond the Patch:

While the immediate threat of CVE-2023-0107 in Memos has been neutralized, understanding potential XSS exploit tactics remains crucial for future preparedness. Here are some additional ways attackers might have exploited the vulnerability:

  • Social Engineering: Tricking users into clicking malicious links or downloading infected files containing weaponized markdown notes.

  • Supply Chain Attacks: Targeting third-party integrations or plugins used by Memos to introduce the vulnerability.

  • Zero-day Exploits: Developing novel exploit techniques beyond the known vulnerability details.

A Call to Action:

CVE-2023-0107 in Memos is a stark reminder that vulnerabilities can emerge in the most unexpected places. However, by embracing a culture of vigilance, education, and responsible software development, we can turn the page on such threats and write a secure future for our digital lives. Let's continue sharing information, updating software responsibly, and practicing safe browsing habits to create a safer and more trustworthy online world for everyone.

Disclaimer:

The information presented in this blog post is for educational purposes only. It is intended to raise awareness about the CVE-2023-0107 vulnerability and help mitigate the risks. It is not intended to be used for malicious purposes.

Exploiting vulnerabilities in live systems without proper authorization is illegal and harmful. This blog post does not advocate or encourage such activities.

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