CVE-2016-7944 – An integer overflow vulnerability in X.org libX... (How to Fix)

Q: What is the severity of CVE-2016-7944?

CVE-2016-7944 has a CVSS score of 9.8 (CRITICAL). An integer overflow vulnerability in X.org libXfixes on 32-bit systems allows remote X servers to trigger a client-server desynchronization by sending a length value of INT_MAX. This could potentially allow privilege escalation or arbitrary code execution. Affects systems running 32-bit X Window System clients with vulnerable libXfixes versions.

📋 TL;DR

An integer overflow vulnerability in X.org libXfixes on 32-bit systems allows remote X servers to trigger a client-server desynchronization by sending a length value of INT_MAX. This could potentially allow privilege escalation or arbitrary code execution. Affects systems running 32-bit X Window System clients with vulnerable libXfixes versions.

💻 Affected Systems

Products:

X.org libXfixes

Versions: Versions before 5.0.3

Operating Systems: Linux, Unix-like systems with 32-bit architecture

Default Config Vulnerable: ⚠️ Yes

Notes: Only affects 32-bit platforms. Requires X client-server communication.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Remote X server gains full control over vulnerable client system, potentially leading to complete system compromise and privilege escalation.

🟠

Likely Case

Client application crashes or becomes unresponsive, leading to denial of service and potential information disclosure.

🟢

If Mitigated

With proper network segmentation and X server authentication, impact limited to isolated client systems.

🌐 Internet-Facing: LOW

🏢 Internal Only: MEDIUM

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Exploitation requires ability to communicate with X client as X server. Proof-of-concept details available in security advisories.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: 5.0.3

Vendor Advisory: https://cgit.freedesktop.org/xorg/lib/libXfixes/commit/?id=61c1039ee23a2d1de712843bed3480654d7ef42e

Restart Required: Yes

Instructions:

1. Update libXfixes to version 5.0.3 or later using your distribution's package manager. 2. Restart X server and affected applications. 3. For source installations: download patched source from X.org and rebuild.

🔧 Temporary Workarounds

Network Segmentation

linux

Restrict X server connections to trusted networks only

iptables -A INPUT -p tcp --dport 6000:6009 -s trusted_network -j ACCEPT
iptables -A INPUT -p tcp --dport 6000:6009 -j DROP

X Authentication

linux

Enforce X authentication to prevent unauthorized server connections

xhost +localhost
xhost -

🧯 If You Can't Patch

Migrate to 64-bit systems where this vulnerability does not exist
Disable remote X connections and use only local X sessions

🔍 How to Verify

Check if Vulnerable:

Check libXfixes version: dpkg -l | grep libxfixes or rpm -qa | grep libXfixes

Check Version:

pkg-config --modversion xfixes

Verify Fix Applied:

Verify version is 5.0.3 or higher: dpkg -l libxfixes3 | grep ^ii

📡 Detection & Monitoring

Log Indicators:

X server connection attempts from untrusted sources
X client crashes with segmentation faults

Network Indicators:

TCP connections to X server ports (6000-6009) from unusual sources
Large data packets sent to X clients

SIEM Query:

source="xorg.log" AND ("segmentation fault" OR "integer overflow")

📊 Metadata

CVE ID: CVE-2016-7944

CVSS v3 Score: 9.8 (CRITICAL)

CVSS Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CWE: CWE-190

Published: December 13, 2016

Last Updated: April 12, 2025

🔗 References

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