CVE-2026-111497: Google Brotli Unchecked Return Value Vulnerability

What happened

Google Brotli contains an unchecked return value vulnerability that allows a remote unauthenticated attacker to corrupt adjacent decoder state memory, disclose sensitive memory contents, cause a denial of service, or potentially execute arbitrary code using a crafted Brotli-compressed stream.

CISA added CVE-2026-111497 to its Known Exploited Vulnerabilities catalog on 2026-10-27, which means there is evidence of real-world attacks.

Who is affected

Organisations running Google Brotli. Check the vendor advisory in the sources for the exact affected versions.

Why it matters

It has a CVSS score of 9.2. Exploitation is already happening, so exposed systems are at immediate risk.

What to do now

Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.

Find every instance of Brotli in your environment, patch internet-facing systems first, and review logs for signs of compromise.

Sources

• CISA Known Exploited Vulnerabilities catalog
• NVD entry for CVE-2026-111497
• https://nvd.nist.gov/vuln/detail/CVE-2026-111497
• https://github.com/andybalholm/brotli/releases/tag/v1.2.7
• https://nodejs.org/en/blog/vulnerability/october-2026-security-releases#nodejs-brotli-decoder-out-of-bounds-write-permits-remote-code-execution-cve-2026-111497---high
• http://www.openwall.com/lists/oss-security/2026/10/23/25
• http://www.openwall.com/lists/oss-security/2026/10/24/6