CVE-2026-111497: Google Brotli Unchecked Return Value Vulnerability
- Is it exploited?
Yes. CISA added it to the Known Exploited Vulnerabilities catalog on 27 Oct 2026, 5 days after the CVE record was published.
- How likely is exploitation in the next 30 days?
- 88%
EPSS score, percentile 99.8 of all scored records
- How severe?
- 9.2 Critical
CVSS v4.0 base score, given by the CNA
- What should I do?
Required action (CISA), due 10 Nov 2026: 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.
- Which versions are affected?
Affected: 1.0.3 up to, not including, 1.0.10; 1.1.0 up to, not including, 1.1.1; 1.2.0 up to, not including, 1.2.1
Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.
What to do
Required action, set by CISA
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.
CISA due date for this action: 10 November 2026.
Solution (from the CVE record)
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.
Advisories and patches
Linked from CISA's catalog entry
- https://github.com/google/brotli/releases/tag/v1.2.1
- https://www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-updates-based-risk
- https://www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-prioritizing-security-updates-based-risk
- https://nvd.nist.gov/vuln/detail/CVE-2026-111497
Affected products and versions
As listed in the CVE record.
| Status | Versions |
|---|---|
| Affected | 1.0.3 up to, not including, 1.0.10 |
| Affected | 1.1.0 up to, not including, 1.1.1 |
| Affected | 1.2.0 up to, not including, 1.2.1 |
Versions not listed are: unaffected.
Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.
About this 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.
Summary: CISA's KEV catalog, as of 28 Oct 2026.
- CISA added CVE-2026-111497 to its Known Exploited Vulnerabilities (KEV) catalog on 27 Oct 2026.
- CISA's ransomware flag for this entry is "Unknown": no evidence of ransomware use in the catalog, which is not proof of none.
- The due date CISA sets for the required action is 10 Nov 2026.
- The CVE record was published on 22 Oct 2026, 5 days before it was added to KEV.
- The CVE record carries a CVSS v4.0 base score of 9.2 (Critical), given by its CNA.
- FIRST's EPSS model puts the probability of exploitation in the next 30 days at 88% (percentile 99.8), as of 28 Oct 2026.
- CISA's SSVC assessment in the CVE record: exploitation none, automatable no, technical impact total.
Source: CISA Known Exploited Vulnerabilities (KEV) catalog, 2026.10.28, as of 28 Oct 2026; CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026; FIRST Exploit Prediction Scoring System (EPSS), v2026.06.15, as of 28 Oct 2026. About the data.
Description
Out-of-Bounds Write in Google Brotli Decoder
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.
Source: CVE List V5 (CVE Program), cve_2026-10-28_0000Z, as of 28 Oct 2026. About the data.
Weakness
Attack patterns (CAPEC)
- CAPEC-100: Overflow Buffers
CWE and CAPEC are maintained by MITRE; the entries are those named in the CVE record and the KEV entry.
Timeline
| Date | Event |
|---|---|
| 22 Oct 2026 | CVE record published |
| 26 Oct 2026 | CVE record last updated |
| 27 Oct 2026 | Added to CISA KEV |
| 10 Nov 2026 | CISA due date for the required action |
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