CVE-2026-124040: CivetWeb through 1.16, when built with USE_HTTP2 and enable_http2 on, contains a use-after-free vulnerability

Q: How do I fix CVE-2026-124040?

civetweb: upgrade to newer than 1.16. Exact commands for each OS are on this page.

Q: Is CVE-2026-124040 being exploited?

CVE-2026-124040 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-124040 affect?

CVE-2026-124040 affects civetweb. Severity is high (CVSS 8.1). CivetWeb through 1.16, when built with USE_HTTP2 and enable_http2 on, contains a use-after-free vulnerability in handle_http2() that retains freed :method and :path pointers. Unauthenticated remote attackers can send a later HEADERS frame o

Routine

HIGH 8.1UPGRADE

CVE-2026-124040 is a high-severity flaw (CVSS 8.1) affecting civetweb. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

CivetWeb through 1.16, when built with USE_HTTP2 and enable_http2 on, contains a use-after-free vulnerability in handle_http2() that retains freed :method and :path pointers. Unauthenticated remote attackers can send a later HEADERS frame omitting these pseudo-headers to influence request method or path seen by access rules, or crash the server.

Why this priority

High severity

A fixed release or distro patch exists.

Risk facts

CVSS score	8.1 (High)
EPSS exploit chance	n/a
CISA exploited list	No
Weakness	CWE-416
Published	2026-11-06
Last modified	2026-11-06

Publisher (CNA): VulnCheck · Vendor: civetweb · Source: CVE Program record (NVD analysis pending)

Last updated 2026-11-06 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-11-06 19:14 UTCPublished CVE record published
2026-11-06 19:14 UTCUpdated Record last modified

civetweb civetweb UPGRADE

Affected: <= 1.16

Fixed in: newer than 1.16

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy civetweb || rpm -q civetweb || civetweb --version

2. UPGRADE to newer than 1.16 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade civetweb

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade civetweb

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-124040?

civetweb: upgrade to newer than 1.16. Exact commands for each OS are on this page.

Is CVE-2026-124040 being exploited?

CVE-2026-124040 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-124040 affect?

CVE-2026-124040 affects civetweb. Severity is high (CVSS 8.1). CivetWeb through 1.16, when built with USE_HTTP2 and enable_http2 on, contains a use-after-free vulnerability in handle_http2() that retains freed :method and :path pointers. Unauthenticated remote attackers can send a later HEADERS frame o

How urgent is CVE-2026-124040?

Priority 28/100. High severity

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References

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