Full Report
Anthropic on Friday said it discovered 22 new security vulnerabilities in the Firefox web browser as part of a security partnership with Mozilla. Of these, 14 have been classified as high, seven have been classified as moderate, and one has been rated low in severity. The issues were addressed in Firefox 148, released late last month. The vulnerabilities were identified over a two-week period in
Analysis Summary
# Vulnerability: Multiple Vulnerabilities Discovered via AI-Assisted Red Teaming (Anthropic/Mozilla Partnership)
## CVE Details
- **CVE ID:** CVE-2026-2796 (Primary highlighted flaw; part of a set of 22 vulnerabilities)
- **CVSS Score:** 9.8 (Critical)
- **CWE:** CWE-670 (Design/Logic Error - JIT Miscompilation) / CWE-416 (Use-After-Free)
## Affected Systems
- **Products:** Mozilla Firefox
- **Versions:** Versions prior to Firefox 148
- **Configurations:** Default installations; specifically affecting the JavaScript WebAssembly (Wasm) component and C++ codebase.
## Vulnerability Description
Anthropic identified 22 security flaws (14 High, 7 Moderate, 1 Low severity) using the Claude Opus 4.6 LLM.
- **CVE-2026-2796:** A Just-In-Time (JIT) miscompilation vulnerability within the JavaScript WebAssembly component. This allows for improper machine code generation, which can lead to memory corruption.
- **General Flaws:** The research identified a significant use-after-free (UAF) bug in the browser's JavaScript engine and various logic errors and assertion failures in over 6,000 C++ files that traditional fuzzing tools had missed.
## Exploitation
- **Status:** PoC available (Developed internally by Anthropic). No reported exploitation in the wild.
- **Complexity:** High (While the AI generated crude exploits, it required stripping security features like sandboxing to succeed).
- **Attack Vector:** Network (Remote via malicious web content).
## Impact
- **Confidentiality:** High (Potential for memory leakage and data theft).
- **Integrity:** High (Potential for arbitrary code execution).
- **Availability:** High (Potential for browser crashes and denial of service).
## Remediation
### Patches
- **Firefox 148:** Users should update to version 148 or later to address the majority of these flaws.
- **Future Releases:** Remaining minor bugs and logic errors are scheduled for patches in upcoming Mozilla release cycles.
### Workarounds
- No specific workarounds are provided; standard browser hardening (enabling Enhanced Online Protection and ensuring sandboxing is active) is recommended.
## Detection
- **Indicators of Compromise:** Unusual browser instability or crashes when processing WebAssembly or complex JavaScript.
- **Detection Methods:** Security teams can monitor for exploitation attempts of CVE-2026-2796 using network signatures targeting known Wasm exploit patterns.
## References
- Mozilla Foundation Security Advisory: [https://www.mozilla.org/en-US/security/advisories/mfsa2026-13/]
- Anthropic Research Blog: [https://www.anthropic.com/news/mozilla-firefox-security]
- Firefox Release Notes: [https://www.firefox.com/en-US/firefox/148.0/releasenotes/]
- NVD Detail: [https://nvd.nist.gov/vuln/detail/CVE-2026-2796]