CVE-2026-111497: flaw exploited in the wild, what we know

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.

• Severity: CRITICAL (CVSS 4.0 9.2, vector 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).
• Weakness: CWE-252, CWE-787.
• NVD published 2026-10-22, status Awaiting Analysis.

Anyone running CVE-2026-111497. Internet-facing instances are the priority.

NVD has not published affected version ranges for this CVE yet. Use the vendor advisory in the sources below to confirm which builds are affected.

• Exploited in the wild: added to the CISA Known Exploited Vulnerabilities catalog on 2026-10-27; federal remediation due date 2026-11-10.
• Public proof-of-concept code: 84 GitHub repositories from 79 accounts, the first on 2026-10-22.

CISA added CVE-2026-111497 to its Known Exploited Vulnerabilities catalog on 2026-10-27. A KEV listing means CISA has evidence that attackers are using the flaw against real systems, not just that it could be used.

If your business runs CVE-2026-111497, put this at the top of the patch list. CISA gave US federal agencies until 2026-11-10 to deal with it, and that is a sensible deadline for a small business too.

• Patch. Install the latest update from the vendor. NVD does not list a fixed version, so the vendor advisory linked on this page is the reference for which release closes it.
• If you cannot patch yet. Follow 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). 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.
• Check your exposure. Find out whether CVE-2026-111497 can be reached from the internet, for example a VPN portal, an admin login page or a file-transfer site. Your firewall's port-forwarding rules and your IT provider's list of public-facing systems are the quickest places to look. Exposed copies come first.
• When to call IT support. Call your IT support provider now if you run CVE-2026-111497 and cannot confirm it is updated, if it was reachable from the internet before you patched it, or if you notice accounts, sign-ins or files you do not recognise. The last two can mean the system was already hit, and checking that properly takes someone who can read the logs.

• EPSS (probability of exploitation activity in the next 30 days): 82.64%, higher than 100% of all scored CVEs (as of 2026-11-03).
• CVERadar threat level: 86/100 (see methodology).
• Likely ATT&CK techniques: T1203 Exploitation for Client Execution (inferred); T1499 Endpoint Denial of Service (inferred); T1190 Exploit Public-Facing Application (inferred).

1. Find every instance. List where CVE-2026-111497 runs, including test, DR and forgotten internet-facing systems, and record the installed version.
2. Apply the latest vendor update. NVD does not list a fixed version, so follow the vendor advisory for the patched release.
3. If you can't patch today, follow 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). 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.
4. Verify the fix. Re-run the version check on every instance and confirm it reports the fixed build. Re-scan from outside if the service is exposed.
5. Hunt for signs of earlier compromise. If the system was exposed before you patched, assume it may have been hit and check the items below.
6. Rotate credentials stored on or used by the affected system if you cannot rule out compromise, and keep the logs you reviewed.

Detection hints

• T1190 Exploit Public-Facing Application: Review WAF, reverse-proxy and application logs for unusual requests to the affected service (odd paths, oversized or encoded payloads, bursts of errors), going back to at least 2026-10-22.
• T1203 Exploitation for Client Execution: Exploitation of client or server software usually shows as crashes of the affected process followed by unexpected child processes; check EDR alerts for both.
• T1499 Endpoint Denial of Service: Monitor availability and crash/restart counts of the affected service.

Detection commands are generic starting points, not CVE-specific signatures. Use the indicators from the vendor advisory when it publishes them.

• NVD: CVE-2026-111497 nvd.nist.gov/vuln/detail/CVE-2026-111497
• CVE.org record www.cve.org/CVERecord?id=CVE-2026-111497
• Vendor link from CISA KEV github.com/google/brotli/releases/tag/v1.2.1
• Vendor link from CISA KEV www.cisa.gov/news-events/directives/bod-26-04-prioritizing-security-up
• Vendor link from CISA KEV www.cisa.gov/news-events/directives/bod-26-04-implementation-guidance-
• CISA KEV catalog www.cisa.gov/known-exploited-vulnerabilities-catalog
• FIRST EPSS (2026-11-03) api.first.org/data/v1/epss?cve=CVE-2026-111497