CVE-2026-25543: HtmlSanitizer is a .NET library for cleaning HTML fragments and documents from constructs that can lead to XSS

Routine

MEDIUM 6.1UPGRADE

CVE-2026-25543 is a medium-severity flaw (CVSS 6.1) affecting htmlsanitizer. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

HtmlSanitizer is a .NET library for cleaning HTML fragments and documents from constructs that can lead to XSS attacks. Prior to versions 9.0.892 and 9.1.893-beta, if the template tag is allowed, its contents are not sanitized. The template tag is a special tag that does not usually render its contents, unless the shadowrootmode attribute is set to open or closed. This issue has been patched in versions 9.0.892 and 9.1.893-beta.

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	6.1 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.3% (top 80%)
CISA exploited list	No
Weakness	CWE-116, CWE-79
Published	2026-02-04
Last modified	2026-06-17

Publisher (CNA): GitHub, Inc. · Vendor: htmlsanitizer project

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-02-04 22:16 UTCPublished CVE record published
2026-06-17 10:24 UTCUpdated Record last modified

htmlsanitizer project htmlsanitizer UPGRADE

Affected: < 9.0.892 · >= 9.1.878 and < 9.1.893

Fixed in: 9.0.892, 9.1.893

Safe to downgrade to: a release before 9.1.878

1. Check installed version

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

2. UPGRADE to 9.0.892 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade htmlsanitizer

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 9.1.878 (Debian / Ubuntu)

apt-cache madison htmlsanitizer sudo apt install htmlsanitizer=<VERSION_BEFORE_9.1.878> sudo apt-mark hold htmlsanitizer

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

dnf --showduplicates list htmlsanitizer sudo dnf downgrade htmlsanitizer-<VERSION_BEFORE_9.1.878> sudo dnf versionlock add htmlsanitizer

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-2026-25543?

htmlsanitizer: upgrade to 9.0.892, 9.1.893. Exact commands for each OS are on this page.

Is CVE-2026-25543 being exploited?

CVE-2026-25543 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-2026-25543 affect?

CVE-2026-25543 affects htmlsanitizer. Severity is medium (CVSS 6.1). HtmlSanitizer is a .NET library for cleaning HTML fragments and documents from constructs that can lead to XSS attacks. Prior to versions 9.0.892 and 9.1.893-beta, if the template tag is allowed, its contents are not sanitized. The template

How urgent is CVE-2026-25543?

Priority 26/100. No elevated risk signals yet.

References

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