CVE-2021-20240
📋 TL;DR
CVE-2021-20240 is an integer overflow vulnerability in gdk-pixbuf's GIF image parser that allows out-of-bounds writes when processing malicious GIF files. This can lead to application crashes or remote code execution, affecting any system using vulnerable versions of gdk-pixbuf to process GIF images. The vulnerability impacts data confidentiality, integrity, and system availability.
💻 Affected Systems
- gdk-pixbuf
- Applications using gdk-pixbuf for GIF processing (e.g., GNOME applications, image viewers)
📦 What is this software?
Fedora by Fedoraproject
Fedora by Fedoraproject
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution with the privileges of the application processing the GIF, potentially leading to full system compromise.
Likely Case
Application crashes (denial of service) when processing malicious GIFs, with potential for limited code execution in some scenarios.
If Mitigated
Application crashes without code execution if memory protections like ASLR are effective, or no impact if GIF processing is disabled.
🎯 Exploit Status
Exploitation requires the victim to process a crafted GIF file, which could be delivered via web, email, or file shares. Public proof-of-concept exists demonstrating crash/DoS.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 2.42.0 and later
Vendor Advisory: https://bugzilla.redhat.com/show_bug.cgi?id=1926787
Restart Required: Yes
Instructions:
1. Update gdk-pixbuf package to version 2.42.0 or later using your distribution's package manager. 2. Restart affected applications or the system to ensure the updated library is loaded.
🔧 Temporary Workarounds
Disable GIF support in gdk-pixbuf
linuxRemove or disable GIF image loader module to prevent processing of GIF files.
sudo mv /usr/lib64/gdk-pixbuf-2.0/2.10.0/loaders/libpixbufloader-gif.so /usr/lib64/gdk-pixbuf-2.0/2.10.0/loaders/libpixbufloader-gif.so.disabled
sudo gdk-pixbuf-query-loaders --update-cache
🧯 If You Can't Patch
- Implement application whitelisting to prevent execution of untrusted applications that process GIFs.
- Use network filtering to block GIF file downloads from untrusted sources and implement user awareness training about opening suspicious image files.
🔍 How to Verify
Check if Vulnerable:
Check gdk-pixbuf version: 'gdk-pixbuf-query-loaders --version' or 'rpm -q gdk-pixbuf2' on RPM systems, 'dpkg -l libgdk-pixbuf2.0-0' on Debian/Ubuntu.Check Version:
gdk-pixbuf-query-loaders --versionVerify Fix Applied:
Verify version is 2.42.0 or higher using the same commands, and test GIF processing in applications.📡 Detection & Monitoring
Log Indicators:
- Application crashes with segmentation faults or memory errors when processing GIF files
- Unexpected process termination in applications using gdk-pixbuf
Network Indicators:
- Unusual GIF file downloads or transfers to systems with vulnerable software
SIEM Query:
Process termination events from applications known to use gdk-pixbuf (e.g., eog, gthumb, nautilus) combined with file access to .gif files🔗 References
- https://bugzilla.redhat.com/show_bug.cgi?id=1926787
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/B5H3GNVWMZTYZR3JBYCK57PF7PFMQBNP/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BGZVCTH5O7WBJLYXZ2UOKLYNIFPVR55D/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/EANWYODLOJDFLMBH6WEKJJMQ5PKLEWML/
- https://bugzilla.redhat.com/show_bug.cgi?id=1926787
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/B5H3GNVWMZTYZR3JBYCK57PF7PFMQBNP/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BGZVCTH5O7WBJLYXZ2UOKLYNIFPVR55D/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/EANWYODLOJDFLMBH6WEKJJMQ5PKLEWML/
