Known exploited vulnerability · CISA KEV

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

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.

CVE-2026-111497

Exploited in the wild. Fix this first.

CISA added it to the Known Exploited Vulnerabilities catalog on 2026-10-27: attackers are using it right now.

CISA KEV: Listed; Added 2026-10-27 · federal fix-by 2026-11-10
EPSS (30 days): 83%; Higher than 99.7% of CVEs · 2026-11-01
CVSS v4.0: 9.2 Critical; CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

What CISA says

Google Brotli Unchecked Return Value Vulnerability

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.

NVD description · published 2026-10-22

A buffer overflow vulnerability in the Brotli decoder (c/dec/decode.c) in Google Brotli versions 1.0.3 through 1.2.0 on all platforms 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. Users need to update any Brotli libraries or binaries between 1.0.3 through 1.2.0 to the latest available version: 1.0.10 or 1.1.1 or 1.2.1.

Full record on NVD

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How to check if you are exposed to CVE-2026-111497

Find every Google Brotli system you or your clients run, including ones exposed to the internet. Those come first: CISA only lists flaws attackers are already using.
Compare each version with the fixed versions in the vendor advisory below. Where no fix exists yet, apply the vendor’s mitigation or take the system off the internet.
Run a credentialed vulnerability scan to catch the systems you missed, then check that the next scan no longer reports CVE-2026-111497.

US federal agencies had to fix this by 2026-11-10. Everyone else should treat that deadline as a guide: if it has passed, this is overdue.

Affected versions

Versions the National Vulnerability Database lists as vulnerable to CVE-2026-111497. Check the vendor advisory for the exact fixed builds before you sign anything off.

Product	Vulnerable versions
Google Brotli	from 1.0.3 before 1.0.10; from 1.1.0 before 1.1.1; from 1.2.0 before 1.2.1
Google Woff2	all versions
Python-Hyper Brotlicffi	before 1.2.1.0
Andybalholm Brotli	before 1.2.7
Nodejs Node.js	before 22.23.4; from 23.0.0 before 24.22.1; from 25.0.0 before 26.12.1
Microsoft .net	from 8.0.0 before 8.0.33; from 9.0.0 before 9.0.22; from 10.0.0 before 10.0.14; 11.0.0-preview1; 11.0.0-preview2; 11.0.0-preview3 and 6 more

NVD lists 19 more affected products; see the full record on NVD.

Timeline

2026-10-22 · Published in the National Vulnerability Database
2026-10-27 · Added to CISA's Known Exploited Vulnerabilities catalog, 5 days after it was published
2026-11-10 · Fix-by date for US federal agencies, still ahead

Vendor advisories and fixes

https://github.com/google/brotli/releases/tag/v1.2.1

Weakness type

More exploited Google vulnerabilities

CISA lists 76 exploited Google vulnerabilities. The closest matches:

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Sources: CISA Known Exploited Vulnerabilities catalog (version 2026.10.30); EPSS data from FIRST.org; CVSS and descriptions from the NIST National Vulnerability Database. Checked 2026-11-01. This product uses the NVD API but is not endorsed or certified by the NVD.