CVE-2016-20011
📋 TL;DR
CVE-2016-20011 is a TLS certificate verification bypass vulnerability in libgrss that allows attackers to perform man-in-the-middle attacks on RSS/Atom feed downloads. This enables attackers to manipulate feed content without detection. Applications using libgrss versions through 0.7.0 to download feeds are affected.
💻 Affected Systems
- libgrss
📦 What is this software?
Libgrss by Gnome
⚠️ Risk & Real-World Impact
Worst Case
Attackers could inject malicious content into RSS/Atom feeds, potentially leading to malware distribution, phishing attacks, or misinformation campaigns when users consume manipulated feeds.
Likely Case
Attackers on the same network could intercept and modify RSS feed content, potentially injecting malicious links or false information that users might trust.
If Mitigated
With proper TLS verification enabled, feed downloads would be protected against man-in-the-middle attacks, ensuring feed integrity and authenticity.
🎯 Exploit Status
Exploitation requires network position to intercept TLS connections. No public exploit code has been documented.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Version 0.7.1 and later
Vendor Advisory: https://gitlab.gnome.org/GNOME/libgrss/-/issues/4
Restart Required: Yes
Instructions:
1. Update libgrss to version 0.7.1 or later using your distribution's package manager. 2. Restart any applications using libgrss. 3. For source installations, download and compile the patched version from the GNOME GitLab repository.
🔧 Temporary Workarounds
Enable TLS certificate verification in application code
linuxModify applications using libgrss to explicitly enable TLS certificate verification when creating SoupSessionSync instances.
// C code example: Set SOUP_SESSION_SSL_STRICT property to TRUE
g_object_set(session, "ssl-strict", TRUE, NULL);
🧯 If You Can't Patch
- Use network segmentation to isolate systems using vulnerable libgrss versions from untrusted networks.
- Monitor network traffic for unexpected RSS feed sources or unusual feed content patterns.
🔍 How to Verify
Check if Vulnerable:
Check libgrss version with: pkg-config --modversion libgrss. If version is 0.7.0 or earlier, the system is vulnerable.Check Version:
pkg-config --modversion libgrssVerify Fix Applied:
Verify libgrss version is 0.7.1 or later using: pkg-config --modversion libgrss📡 Detection & Monitoring
Log Indicators:
- Unexpected RSS feed source changes
- Failed TLS certificate validation warnings in application logs
Network Indicators:
- Unencrypted RSS feed downloads when TLS was expected
- TLS connections to RSS feeds without certificate validation
SIEM Query:
Search for network connections to RSS/Atom feeds without TLS handshake completion or certificate validation events.🔗 References
- https://bugzilla.gnome.org/show_bug.cgi?id=772647
- https://gitlab.gnome.org/GNOME/libgrss/-/issues/4
- https://gitlab.gnome.org/GNOME/libgrss/-/merge_requests/7.patch
- https://bugzilla.gnome.org/show_bug.cgi?id=772647
- https://gitlab.gnome.org/GNOME/libgrss/-/issues/4
- https://gitlab.gnome.org/GNOME/libgrss/-/merge_requests/7.patch
