CVE-2026-66843: Inclusion of Functionality from Untrusted Control Sphere vulnerability in the HTML5 scrubber in rrrene html_sa

Routine

MEDIUM 6.1UPGRADE

CVE-2026-66843 is a medium-severity flaw (CVSS 6.1) affecting htmlsanitizeex. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Inclusion of Functionality from Untrusted Control Sphere vulnerability in the HTML5 scrubber in rrrene html_sanitize_ex allows a remote attacker to load a document of their choosing into a trusted page via the data attribute of an <object> element in sanitized HTML. object is the one URI-bearing element in lib/html_sanitize_ex/scrubber/html5.ex never registered through allow_tag_with_uri_attributes/3, and its only guard is a prefix match on lower

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	0.5% (top 57%)
CISA exploited list	No
Weakness	CWE-829
Published	2026-08-06
Last modified	2026-10-23

Publisher (CNA): EEF · Vendor: rrrene

Last updated 2026-10-23 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-08-06 16:16 UTCPublished CVE record published
2026-10-23 21:10 UTCUpdated Record last modified

rrrene htmlsanitizeex UPGRADE

Affected: >= 0.3.1 and < 1.5.3

Fixed in: 1.5.3

Safe to downgrade to: a release before 0.3.1

1. Check installed version

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

2. UPGRADE to 1.5.3 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade htmlsanitizeex

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 0.3.1 (Debian / Ubuntu)

apt-cache madison htmlsanitizeex sudo apt install htmlsanitizeex=<VERSION_BEFORE_0.3.1> sudo apt-mark hold htmlsanitizeex

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

dnf --showduplicates list htmlsanitizeex sudo dnf downgrade htmlsanitizeex-<VERSION_BEFORE_0.3.1> sudo dnf versionlock add htmlsanitizeex

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-2026-66843?

htmlsanitizeex: upgrade to 1.5.3. Exact commands for each OS are on this page.

Is CVE-2026-66843 being exploited?

CVE-2026-66843 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-2026-66843 affect?

CVE-2026-66843 affects htmlsanitizeex. Severity is medium (CVSS 6.1). Inclusion of Functionality from Untrusted Control Sphere vulnerability in the HTML5 scrubber in rrrene html_sanitize_ex allows a remote attacker to load a document of their choosing into a trusted page via the data attribute of an <object>

How urgent is CVE-2026-66843?

Priority 32/100. No elevated risk signals yet.

Related CVEs

CVE-2026-68749 HIGH 7.5 UPGRADE Inefficient Regular Expression Complexity vulnerability in the CSS scrubber in rrrene html_sanitize_ex allows
CVE-2026-68750 HIGH 7.5 UPGRADE Inefficient Algorithmic Complexity vulnerability in the traversal engine in rrrene html_sanitize_ex allows an
CVE-2026-66829 MEDIUM 6.1 UPGRADE URL Redirection to Untrusted Site ('Open Redirect') vulnerability in the HTML5 scrubber in rrrene html_sanitiz
CVE-2026-68747 MEDIUM 6.1 UPGRADE Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection') vulnerabili
CVE-2026-66370 MEDIUM 6.1 UPGRADE URL Redirection to Untrusted Site ('Open Redirect') vulnerability in the HTML5 scrubber in rrrene html_sanitiz

References

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