CVE-2023-6856
📋 TL;DR
This CVE describes a heap buffer overflow vulnerability in Firefox's WebGL DrawElementsInstanced method when used with Mesa VM driver. An attacker could exploit this to execute arbitrary code and potentially escape browser sandbox protections. Affected users include those running Firefox ESR <115.6, Thunderbird <115.6, or Firefox <121.
💻 Affected Systems
- Firefox ESR
- Thunderbird
- Firefox
📦 What is this software?
Firefox by Mozilla
Firefox Esr by Mozilla
Thunderbird by Mozilla
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution leading to full system compromise, sandbox escape, and attacker gaining persistent access to the system.
Likely Case
Browser crash or arbitrary code execution within browser context, potentially leading to data theft or malware installation.
If Mitigated
Limited impact if browser sandbox holds, potentially just browser crash without system compromise.
🎯 Exploit Status
Exploitation requires user to visit malicious website with WebGL content; no authentication needed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Firefox ESR 115.6, Thunderbird 115.6, Firefox 121
Vendor Advisory: https://bugzilla.mozilla.org/show_bug.cgi?id=1843782
Restart Required: Yes
Instructions:
1. Open affected application. 2. Go to Help > About Firefox/Thunderbird. 3. Allow automatic update or download latest version from official Mozilla website. 4. Restart application after update.
🔧 Temporary Workarounds
Disable WebGL
allPrevents WebGL rendering which mitigates the vulnerability but breaks WebGL-dependent websites.
about:config
Set webgl.disabled to true
Use alternative browser
allTemporarily switch to unaffected browser until patches are applied.
🧯 If You Can't Patch
- Restrict access to untrusted websites and disable JavaScript execution for unknown sites
- Implement network filtering to block WebGL content from untrusted sources
🔍 How to Verify
Check if Vulnerable:
Check browser version: Firefox/Thunderbird: Help > About. If version is below patched versions and running on Linux with Mesa, system is vulnerable.Check Version:
firefox --version or thunderbird --version on Linux command lineVerify Fix Applied:
Verify browser version is at least Firefox ESR 115.6, Thunderbird 115.6, or Firefox 121.📡 Detection & Monitoring
Log Indicators:
- Browser crash logs with WebGL context
- Unexpected process termination of Firefox/Thunderbird
Network Indicators:
- HTTP requests to websites serving WebGL content followed by browser crashes
SIEM Query:
source="firefox.log" AND ("crash" OR "segfault") AND "WebGL"🔗 References
- https://bugzilla.mozilla.org/show_bug.cgi?id=1843782
- https://lists.debian.org/debian-lts-announce/2023/12/msg00020.html
- https://lists.debian.org/debian-lts-announce/2023/12/msg00021.html
- https://security.gentoo.org/glsa/202401-10
- https://www.debian.org/security/2023/dsa-5581
- https://www.debian.org/security/2023/dsa-5582
- https://www.mozilla.org/security/advisories/mfsa2023-54/
- https://www.mozilla.org/security/advisories/mfsa2023-55/
- https://www.mozilla.org/security/advisories/mfsa2023-56/
- https://bugzilla.mozilla.org/show_bug.cgi?id=1843782
- https://lists.debian.org/debian-lts-announce/2023/12/msg00020.html
- https://lists.debian.org/debian-lts-announce/2023/12/msg00021.html
- https://security.gentoo.org/glsa/202401-10
- https://www.debian.org/security/2023/dsa-5581
- https://www.debian.org/security/2023/dsa-5582
- https://www.mozilla.org/security/advisories/mfsa2023-54/
- https://www.mozilla.org/security/advisories/mfsa2023-55/
- https://www.mozilla.org/security/advisories/mfsa2023-56/
