EEF-CVE-2026-66829 CVE-2026-66829 GHSA-2c6f-3j54-xpcr
html_sanitize_ex HTML5 scrubber keeps attacker-supplied meta refresh, allowing forced cross-origin redirection
- Severity
- 0.0 / 10
- Medium · CVSS 4.0
- Exploit chance (EPSS)
- 0.57%
- Chance of exploitation in the next 30 days. Higher than 47.01% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-601 URL Redirection to Untrusted Site ('Open Redirect')
- Fix
1.5.3- Upgrade html_sanitize_ex to this version or later
Description
Summary
URL Redirection to Untrusted Site ('Open Redirect') vulnerability in the HTML5 scrubber in rrrene html_sanitize_ex allows a remote attacker to force visitors of a page to navigate to a site of the attacker's choosing via a <meta http-equiv="refresh"> element in sanitized HTML. HtmlSanitizeEx.html5/1 keeps attacker-supplied <meta> elements in its output. A meta element acts on the whole document rather than on the fragment it was embedded in, so it can also declare document-wide directives such as Content-Security-Policy.
This is not cross-site scripting. Browsers do not navigate a meta refresh to a javascript: URL, so the uppercase JAVASCRIPT: filter bypass yields no script execution and none was demonstrated.
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.
Workarounds
Sanitize with basic_html/1, markdown_html/1 or strip_tags/1, none of which allow meta, or define a custom scrubber that omits it.
Configurations
Only HtmlSanitizeEx.html5/1, and custom scrubbers declared with use HtmlSanitizeEx, extend: :html5, allow the meta element, and the sanitized output must be rendered to other users.
Affected versions
Hex
| Package | Vulnerable | Fixed in |
|---|---|---|
| html_sanitize_ex | >= 0.3.1, < 1.4.5>= 1.5.0-rc.0, < 1.5.3 |
1.4.51.5.3 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
html_sanitize_ex Hex → 1.5.3
- mix
{:html_sanitize_ex, "~> 1.5.3"} # then: mix deps.update html_sanitize_ex
Severity breakdown
CVSS 4.0 0.0
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N
- Attack vector
- Network
- Attack complexity
- Low
- Attack requirements
- Present
- Privileges required
- None
- User interaction
- Passive
- Confidentiality (vulnerable system)
- None
- Integrity (vulnerable system)
- None
- Availability (vulnerable system)
- None
- Confidentiality (subsequent systems)
- None
- Integrity (subsequent systems)
- Low
- Availability (subsequent systems)
- None
CVSS 3.1 6.1
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- Required
- Scope
- Changed
- Confidentiality
- Low
- Integrity
- Low
- Availability
- None
Weakness
CWE-601: URL Redirection to Untrusted Site ('Open Redirect')
The web application accepts a user-controlled input that specifies a link to an external site, and uses that link in a redirect.
How to prevent it
- Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright. Use a list of approved URLs or domains to be used for redirection.
- Architecture and Design: Use an intermediate disclaimer page that provides the user with a clear warning that they are leaving the current site. Implement a long timeout before the redirect occurs, or force the user to click on the link. Be careful to avoid XSS problems (CWE-79) when generating the disclaimer page.
- Architecture and Design: When the set of acceptable objects, such as filenames or URLs, is limited or known, create a mapping from a set of fixed input values (such as numeric IDs) to the actual filenames or URLs, and reject all other inputs. For example, ID 1 could map to "/login.asp" and ID 2 could map to "http://www.example.com/". Features such as the ESAPI AccessReferenceMap [REF-45] provide this capability.
- Architecture and Design: Ensure that no externally-supplied requests are honored by requiring that all redirect requests include a unique nonce generated by the application [REF-483]. Be sure that the nonce is not predictable (CWE-330).
- Architecture and Design, Implementation: Understand all the potential areas where untrusted inputs can enter your software: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide data to the application. Remember that such inputs may be obtained indirectly through API calls. Many open redirect problems occur because the programmer assumed that certain inputs could not be modified, such as cookies and hidden form fields.
- Operation: Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth [REF-1481].
References
Advisories
Fixes and patches
Packages
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| EEF-CVE-2026-68750 Quadratic sibling re-flattening in the html_sanitize_ex traversal engine allows CPU-exhaustion denial of service | High | Also affects html_sanitize_ex |
| EEF-CVE-2026-68749 Quadratic regex backtracking in the html_sanitize_ex CSS scrubber allows CPU-exhaustion denial of service | High | Also affects html_sanitize_ex |
| EEF-CVE-2026-68747 CSS sanitizer allowlist bypass in html_sanitize_ex via non-declaration input | Medium | Also affects html_sanitize_ex |
| EEF-CVE-2026-66370 html_sanitize_ex HTML5 scrubber keeps attacker-supplied form-association attributes, allowing form hijacking | Medium | Also affects html_sanitize_ex |
| EEF-CVE-2026-66843 html_sanitize_ex HTML5 scrubber keeps attacker-supplied `<object>` elements, allowing untrusted content embedding | Medium | Also affects html_sanitize_ex |
| GHSA-pfhg-q3qv-9q6r SvelteKit: URL redirection to untrusted site via enhanced form submission | Medium | Same weakness, CWE-601 |
| GHSA-w84c-53h3-mc2g Payload: Untrusted redirect URL parameter exploit | Medium | Same weakness, CWE-601 |
| GHSA-r4gj-5m52-g5wh Axios: maxRedirects: 0 is not enforced by the fetch adapter, allowing redirect-based SSRF | High | Same weakness, CWE-601 |
Credits: Jonatan Männchen / EEF, Peter Ullrich, René Föhring
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