CVE-2026-6653: Use After Free in libxml2's xmlParseInternalSubset from GNOME libxml2 version 2.9.11 to 2.11.0 allows a remote

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CRITICAL 9.8REMOTEUPGRADE

CVE-2026-6653 is a critical-severity flaw (CVSS 9.8) affecting libxml2. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Use After Free in libxml2's xmlParseInternalSubset from GNOME libxml2 version 2.9.11 to 2.11.0 allows a remote attacker to cause a denial-of-service via maliciously crafted XML input with improper entity resolution handling.

Why this priority

Critical severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 71%)
CISA exploited list	No
Weakness	CWE-416, CWE-611
Published	2026-06-22
Last modified	2026-10-25

Publisher (CNA): Canonical Ltd. · Vendor: xmlsoft

Last updated 2026-10-25 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-06-22 14:17 UTCPublished CVE record published
2026-10-25 23:10 UTCUpdated Record last modified

xmlsoft libxml2 UPGRADE

Affected: >= 2.9.11 and <= 2.11.0

Fixed in: newer than 2.11.0

Safe to downgrade to: a release before 2.9.11

1. Check installed version

apt-cache policy libxml2 || rpm -q libxml2 || libxml2 --version

2. UPGRADE to newer than 2.11.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade libxml2

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade libxml2

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 2.9.11 (Debian / Ubuntu)

apt-cache madison libxml2 sudo apt install libxml2=<VERSION_BEFORE_2.9.11> sudo apt-mark hold libxml2

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

dnf --showduplicates list libxml2 sudo dnf downgrade libxml2-<VERSION_BEFORE_2.9.11> sudo dnf versionlock add libxml2

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.

Advisories and coverage

Official advisories

CISA Alerts and Advisories: Hitachi Energy RTU500 Product 2026-10-20

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-2026-6653?

libxml2: upgrade to newer than 2.11.0. Exact commands for each OS are on this page.

Is CVE-2026-6653 being exploited?

CVE-2026-6653 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-2026-6653 affect?

CVE-2026-6653 affects libxml2. Severity is critical (CVSS 9.8). Use After Free in libxml2's xmlParseInternalSubset from GNOME libxml2 version 2.9.11 to 2.11.0 allows a remote attacker to cause a denial-of-service via maliciously crafted XML input with improper entity resolution handling.

How urgent is CVE-2026-6653?

Priority 52/100. Critical severity; Public exploit reference; Remotely exploitable, no login, no user action

Software pages

libxml2 vulnerabilities

Related CVEs

CVE-2026-11979 HIGH 7.8 UPGRADE libxml2 is vulnerable to multiple stack-based buffer overflows in the xmlcatalog utility when running in --she

References

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