CVE-2026-66843 html_sanitize_ex HTML5 scrubber keeps attacker-supplied `<object>` elements, allowing untrusted content embedding
Attackers can embed untrusted content via object tags in sanitized HTML, potentially leading to script execution or content injection in trusted pages.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-66843?
CVE-2026-66843 is a low-severity cross-site scripting vulnerability in rrrene html_sanitize_ex, published on 6 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official 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.
Weakness: CWE-829
Which versions are affected by CVE-2026-66843?
1 open source package ship an affected version, including html_sanitize_ex. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
html_sanitize_ex Hex | From 0.3.1 | 1.4.5, 1.5.3 |
Products include Rrrene Htmlsanitizeex.
How do I fix CVE-2026-66843?
Upgrade html_sanitize_ex to a fixed version for your release line: 1.4.5 or 1.5.3.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-66843 being exploited?
There is no known exploitation of CVE-2026-66843 in the wild and no public exploit code.
Other vulnerabilities in rrrene html_sanitize_ex
- CVE-2026-68749 Quadratic regex backtracking in the html_sanitize_ex CSS scrubber allows CPU-exhaustion denial of service
- CVE-2026-68750 Quadratic sibling re-flattening in the html_sanitize_ex traversal engine allows CPU-exhaustion denial of service
- CVE-2026-66370 html_sanitize_ex HTML5 scrubber keeps attacker-supplied form-association attributes, allowing form hijacking
- CVE-2026-66829 html_sanitize_ex HTML5 scrubber keeps attacker-supplied meta refresh, allowing forced cross-origin redirection
- CVE-2026-68747 CSS sanitizer allowlist bypass in html_sanitize_ex via non-declaration input
Sources
Also known as EEF-CVE-2026-66843, GHSA-6g7x-33rf-28v3, GHSA-xmm9-jc22-rcgj.