CVE-2026-111497
CVE-2026-111497 is a security flaw in Google Brotli. Attackers can run their own code on Google Brotli from anywhere, without logging in. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 27 Oct 2026.[1]
Google Brotli is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. Fixed in version 1.0.10, 1.1.1 and 1.2.1 of Brotli.
Description
CISA calls it an unchecked return value in Google Brotli. In its words: “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.”[1]
The CVE record adds: “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.”[2]
The underlying weakness is CWE-252, out-of-bounds write (CWE-787), in MITRE’s list of common software weaknesses.
It scores 9.8 out of 10 on the Common Vulnerability Scoring System, which rates it critical, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record lists these fixed versions: in each line, everything before the version shown is affected.[2]
| Product | Fixed in |
|---|---|
| Brotli | 1.0.10 |
| Brotli | 1.1.1 |
| Brotli | 1.2.1 |
Most families won’t have Google Brotli; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 27 Oct 2026, 5 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 10 Nov 2026 to fix it.[1]
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 83%. That’s in the top 1% of the flaws it scores.[3]
CISA assesses it as not automatable: each attack takes some work.
CISA doesn’t say who was attacked, or how.
Fix
CISA’s required action: “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).”[1]
- Check whether you use it.Google Brotli is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
- Send this page to your IT person.Ask them to confirm it’s fixed (fixed in version 1.0.10, 1.1.1 and 1.2.1 of Brotli), or not in use. CISA gave US government agencies until 10 Nov 2026 to fix it.
- If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.
You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 9.8.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at 83%.[3] | |
| CISA’s deadline for US government agencies to fix it.[1] |
See also
Other Google flaws
- CVE-2026-58704, Google Pixel: improper authorization ·
- CVE-2026-87491, Chrome and other Chromium browsers: out of bounds write ·
- CVE-2026-85046, Chrome and other Chromium browsers: type confusion ·
- CVE-2026-11645, Chrome and other Chromium browsers: out-of-bounds read and write ·
- CVE-2026-5281, Google Dawn: use-after-free ·
Added the same day
- CVE-2026-48356, Adobe Commerce and Magento: unrestricted upload of file with dangerous type ·
Every Google flaw on CISA’s list · Everything added in October 2026
References
- ^ Cybersecurity and Infrastructure Security Agency. “Google Brotli Unchecked Return Value Vulnerability”. Known Exploited Vulnerabilities Catalog, added 27 Oct 2026.
- ^ National Institute of Standards and Technology. “CVE-2026-111497 Detail”. National Vulnerability Database, published 22 Oct 2026.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.826, percentile 99.7, 31 Oct 2026.
- CVE Program. “CVE-2026-111497”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.