ModSecurity Apache Vulnerability: Bypass Risk Due to Improper Handling of Null Bytes
Summary
DEBIAN-CVE-2023-24021: Incorrect handling of '\0' bytes in file uploads in ModSecurity before 2.9.7 may allow for Web Application Firewall bypasses and buffer over-reads on the Web Application Firewall when executing rules that read the FILES_... Affects modsecurity-apache versions < 2.9.3-3+deb11u2. Fixed in 2.9.3-3+deb11u2. How to fix ↓
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Background
ModSecurity is an open-source web application firewall (WAF) designed to protect web applications from various attacks by monitoring and filtering HTTP traffic. It is widely used in conjunction with Apache web servers to enhance security. The package is known for its ability to enforce security policies and detect vulnerabilities. However, a recent vulnerability has been identified that affects its ability to handle file uploads correctly, specifically concerning null bytes ('\0').
Vulnerability Detail
The vulnerability arises from incorrect handling of '\0' bytes in file uploads in ModSecurity versions prior to 2.9.7. This flaw may allow attackers to bypass the Web Application Firewall (WAF) protections and potentially exploit buffer over-reads when executing rules that interact with the FILES_TMP_CONTENT collection. As a result, this could lead to unauthorized access or manipulation of sensitive data, posing a significant risk to web applications relying on ModSecurity for security.
How To Fix
Minimum fixed version
2.9.3-3+deb11u2
This is the first release that contains the fix.
sudo apt-get install --only-upgrade modsecurity-apacheTip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
As a temporary workaround, consider disabling file upload features or implementing additional validation checks on file uploads to mitigate the risk of exploitation until the package is updated.
Conclusion
The identified vulnerability in ModSecurity related to the handling of null bytes poses a significant risk to web applications. It is crucial for users to update their ModSecurity installations to the latest patched versions to safeguard against potential exploits. Additionally, utilizing tools like Vulert can help in monitoring and managing vulnerabilities effectively.
See every vulnerability recorded for modsecurity-apache →
FAQ
The vulnerability involves improper handling of null bytes in file uploads, which can lead to WAF bypasses and buffer over-reads.
Versions prior to 2.9.7 are affected, with specific fixes available in versions 2.9.3-3+deb11u2 for Debian 11 and 2.9.7-1 for Debian 12, 13, and 14.
You can use Vulert's playground at Vulert Scanner to check if your application is affected by this vulnerability without needing to sign up.
Exploitation of this vulnerability could allow attackers to bypass security measures, leading to unauthorized access or manipulation of sensitive data.
Yes, Vulert can monitor and alert you in real-time for open-source vulnerabilities in your software using just a manifest file like package-lock.json.
References
Related vulnerabilities
Recent vulnerabilities recorded for modsecurity-apache.
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