CVE-2026-66843

Q: How do I fix CVE-2026-66843?

Upgrade htmlsanitizeex to 1.5.3 or later.

Q: Is CVE-2026-66843 being actively exploited?

Not that we know of. CVE-2026-66843 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.29% is the estimated probability that it will be exploited in the next 30 days. That is higher than 21% of all scored CVEs.

Q: How severe is CVE-2026-66843?

CVE-2026-66843 has a CVSS v3 base score of 6.1, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

Q: What does CVE-2026-66843 affect?

Published advisories record a fix for htmlsanitizeex (NVD). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

MEDIUM

6.1

CVSS v3

NVD

Description

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 lowercase "javascript:", so mixed-case variants, data: URIs, protocol-relative URLs and same-origin paths all survive. This is not unconditional cross-site scripting. A javascript: URL does not execute through <object data> in current browsers, data: documents load in an opaque origin, and host-origin script execution additionally requires the application to serve attacker-controlled content from a same-origin path. This issue affects html_sanitize_ex: from 0.3.1 before 1.4.5 and from 1.5.0-rc.0 before 1.5.3.

CWE-829

How to fix

Remediation Available

htmlsanitizeexNVD

Affected:>= 0.3.1, < 1.5.3Fixed in:1.5.3CVE-2026-66843derived from NVD

TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionRequired

ScopeChanged

Impact

ConfidentialityLow

IntegrityLow

AvailabilityNone

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Exploit Intelligence

0.29%probability of exploitation in 30 days

21stpercentile

Low risk: more likely to be exploited than 21% of all known CVEs.

References

Patch3

Other references2

Related Vulnerabilities

Other CWE-829 vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2018-17246	Critical	9.8	82%	-	Fix
CVE-2024-5762	High	8.1	72%	-	-
CVE-2026-0770	Critical	9.8	63%	KEV	-
CVE-2018-7422	High	7.5	62%	-	-
CVE-2023-2249	High	8.8	61%	-	-
CVE-2025-32463	Critical	9.3	59%	KEV	Fix

Common questions

How do I fix CVE-2026-66843?

Upgrade htmlsanitizeex to 1.5.3 or later.

Is CVE-2026-66843 being actively exploited?

Not that we know of. CVE-2026-66843 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.29% is the estimated probability that it will be exploited in the next 30 days. That is higher than 21% of all scored CVEs.

How severe is CVE-2026-66843?

CVE-2026-66843 has a CVSS v3 base score of 6.1, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

What does CVE-2026-66843 affect?

Published advisories record a fix for htmlsanitizeex (NVD). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

Embed a live status badge for CVE-2026-66843

Markdown

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-08-19.