Critical Vulnerability in python-h11: Potential HTTP Request Smuggling
Summary
USN-7503-1: python-h11 vulnerability. Affects python-h11 versions < 0.14.0-1ubuntu0.24.04.1. Fixed in 0.14.0-1ubuntu0.24.04.1. How to fix ↓
Check if this vulnerability affects your application
Upload a manifest or SBOM and we'll show whether you're affected, plus every other risky package in the same scan.
No signup required · Results in about 60 seconds
Habilume
Habit tracker with a companion that grows with you
Complete habits, earn Lume Points, and watch your Lume grow as you stay consistent.
Background
python-h11 is a popular library in Python for handling HTTP/1.1 requests and responses. It is designed to be a lightweight and efficient tool for developers needing to implement HTTP in their applications. However, a recent vulnerability has been identified that affects its ability to properly handle crafted HTTP requests, which could lead to serious security issues.
Vulnerability Detail
Jeppe Bonde Weikop discovered that h11 incorrectly handled crafted HTTP requests. A remote attacker could exploit this vulnerability to smuggle malicious HTTP requests, potentially leading to security control bypass and information leakage. This vulnerability is identified as CVE-2025-43859 and affects versions of python-h11 prior to 0.14.0-1ubuntu0.24.04.1 and 0.14.0-1ubuntu0.25.04.1.
How To Fix
Minimum fixed version
0.14.0-1ubuntu0.24.04.1
This is the first release that contains the fix.
sudo apt-get install --only-upgrade python-h11Tip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
As a temporary workaround, you may consider implementing additional validation on incoming HTTP requests to mitigate the risk of malicious payloads until the package can be updated.
Conclusion
The python-h11 vulnerability presents a significant risk due to its potential for HTTP request smuggling. It is crucial for users to update to the latest patched versions to safeguard their applications against potential attacks. Regular monitoring for vulnerabilities using tools like Vulert can help maintain security.
See every vulnerability recorded for python-h11 →
FAQ
The vulnerability allows for crafted HTTP requests to be improperly handled, which could lead to security control bypass and information leakage.
You can use the Vulert playground at Vulert Scanner to check if your application is affected by this vulnerability without any signup.
Versions prior to 0.14.0-1ubuntu0.24.04.1 and 0.14.0-1ubuntu0.25.04.1 are affected by this vulnerability.
Yes, the patched versions are 0.14.0-1ubuntu0.24.04.1 for Ubuntu 24.04 and 0.14.0-1ubuntu0.25.04.1 for Ubuntu 25.04.
If immediate updates are not possible, consider implementing additional validation on incoming HTTP requests as a temporary workaround.
References
Related vulnerabilities
Recent vulnerabilities recorded for python-h11.
Habilume
Habit tracker with a companion that grows with you
Complete habits, earn Lume Points, and watch your Lume grow as you stay consistent.
