CVE-2026-12523: Summary Cloudflare quiche's HTTP/3 layer was discovered to be vulnerable to resource exhaustion (i.e., memo

This month

HIGH 7.5REMOTEUPGRADE

CVE-2026-12523 is a high-severity flaw (CVSS 7.5) affecting quiche. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Summary Cloudflare quiche's HTTP/3 layer was discovered to be vulnerable to resource exhaustion (i.e., memory) by means of specially crafted HTTP/3 frames. Impact HTTP/3 defines multiple frame types to support HTTP message exchanges and connection management. Each frame has a length and a payload whose length depends on the frame type. quiche was found to be vulnerable when parsing some frame types to pre-allocating memory based on the

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.5% (top 56%)
CISA exploited list	No
Weakness	CWE-400
Published	2026-07-14
Last modified	2026-10-24

Publisher (CNA): Cloudflare, Inc. · Vendor: cloudflare

Last updated 2026-10-24 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-14 16:16 UTCPublished CVE record published
2026-10-24 21:10 UTCUpdated Record last modified

cloudflare quiche UPGRADE

Affected: >= 0.1.0 and < 0.29.3

Fixed in: 0.29.3

Safe to downgrade to: a release before 0.1.0

1. Check installed version

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

2. UPGRADE to 0.29.3 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade quiche

Note

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

3. If no update is available yet, DOWNGRADE to a release before 0.1.0 (Debian / Ubuntu)

apt-cache madison quiche sudo apt install quiche=<VERSION_BEFORE_0.1.0> sudo apt-mark hold quiche

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list quiche sudo dnf downgrade quiche-<VERSION_BEFORE_0.1.0> sudo dnf versionlock add quiche

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

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-2026-12523?

quiche: upgrade to 0.29.3. Exact commands for each OS are on this page.

Is CVE-2026-12523 being exploited?

CVE-2026-12523 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-2026-12523 affect?

CVE-2026-12523 affects quiche. Severity is high (CVSS 7.5). Summary Cloudflare quiche's HTTP/3 layer was discovered to be vulnerable to resource exhaustion (i.e., memory) by means of specially crafted HTTP/3 frames. Impact HTTP/3 defines multiple frame types to support HTTP message exchang

How urgent is CVE-2026-12523?

Priority 42/100. High severity; Remotely exploitable, no login, no user action

Software pages

Cloudflare vulnerabilities

References

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