CVE-2016-7947 – CVE-2016-7947 is a critical vulnerability in X.... (How to Fix)

Q: What is the severity of CVE-2016-7947?

CVE-2016-7947 has a CVSS score of 9.8 (CRITICAL). CVE-2016-7947 is a critical vulnerability in X.org libXrandr library where multiple integer overflows allow remote X servers to trigger out-of-bounds write operations via crafted responses. This can lead to arbitrary code execution or system crashes. Systems using X Window System with vulnerable libXrandr versions are affected.

📋 TL;DR

CVE-2016-7947 is a critical vulnerability in X.org libXrandr library where multiple integer overflows allow remote X servers to trigger out-of-bounds write operations via crafted responses. This can lead to arbitrary code execution or system crashes. Systems using X Window System with vulnerable libXrandr versions are affected.

💻 Affected Systems

Products:

X.org libXrandr
X Window System
Linux distributions with X11

Versions: libXrandr versions before 1.5.1

Operating Systems: Linux, Unix-like systems with X11

Default Config Vulnerable: ✅ No

Notes: Requires X server to be running and accessible to untrusted clients. Most modern systems use Wayland by default.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Remote code execution with root privileges leading to complete system compromise

🟠

Likely Case

Denial of service through application or system crashes

🟢

If Mitigated

Limited impact if network access to X server is restricted and proper input validation is in place

🌐 Internet-Facing: MEDIUM - Requires X server exposure to untrusted networks, which is uncommon in default configurations

🏢 Internal Only: HIGH - Internal attackers or compromised systems could exploit this to escalate privileges

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: MEDIUM

Exploitation requires network access to X server. Proof-of-concept code exists in security advisories.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: libXrandr 1.5.1 and later

Vendor Advisory: https://cgit.freedesktop.org/xorg/lib/libXrandr/commit/?id=a0df3e1c7728205e5c7650b2e6dce684139254a6

Restart Required: Yes

Instructions:

1. Update libXrandr package to version 1.5.1 or later. 2. Restart X server or affected applications. 3. For Linux distributions, use package manager: 'sudo apt-get update && sudo apt-get upgrade libxrandr2' (Debian/Ubuntu) or 'sudo yum update libXrandr' (RHEL/CentOS).

🔧 Temporary Workarounds

Restrict X Server Network Access

linux

Disable TCP listening on X server to prevent remote exploitation

xhost -localhost
Edit /etc/X11/xinit/xserverrc to add '-nolisten tcp'

Use X11 Security Extensions

linux

Enable X Security extension to restrict client connections

xhost +si:localuser:$(whoami)

🧯 If You Can't Patch

Disable X server network access completely using '-nolisten tcp' flag
Implement network segmentation to isolate X servers from untrusted networks

🔍 How to Verify

Check if Vulnerable:

Check libXrandr version: 'dpkg -l libxrandr2' (Debian) or 'rpm -q libXrandr' (RHEL)

Check Version:

ldconfig -p | grep libXrandr && Xrandr --version

Verify Fix Applied:

Verify version is 1.5.1 or higher: 'Xrandr --version' should show 1.5.1+

📡 Detection & Monitoring

Log Indicators:

X server crash logs in /var/log/Xorg.0.log
Segmentation faults in X client applications

Network Indicators:

Unusual X protocol traffic on port 6000+
Malformed XRandR extension requests

SIEM Query:

source="Xorg.0.log" AND ("segmentation fault" OR "crash" OR "BadLength")

📊 Metadata

CVE ID: CVE-2016-7947

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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