EmilStenstrom justhtml up to 1.14.x URL Sanitization Helpers clean_url_value/clean_url_in_js_string injection

Summaryinfo

A vulnerability described as critical has been identified in EmilStenstrom justhtml up to 1.14.x. This impacts the function clean_url_value/clean_url_in_js_string of the component URL Sanitization Helpers. Executing a manipulation can lead to injection. This vulnerability is handled as CVE-2026-5388. The attack can be executed remotely. There is not any exploit available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability has been found in EmilStenstrom justhtml up to 1.14.x and classified as critical. This vulnerability affects the function clean_url_value/clean_url_in_js_string of the component URL Sanitization Helpers. The manipulation with an unknown input leads to a injection vulnerability. The CWE definition for the vulnerability is CWE-74. The product constructs all or part of a command, data structure, or record using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify how it is parsed or interpreted when it is sent to a downstream component. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

justhtml before 1.15.0 contains multiple security issues in URL sanitization helpers (clean_url_value/clean_url_in_js_string), HTML serialization, Markdown passthrough (html_passthrough=True), and several custom sanitization-policy edge cases. Depending on configuration, an attacker can bypass sanitization to inject active HTML and JavaScript — for example via encoded javascript: URLs, backslash-based relative URLs resolved as remote hosts, markup-breaking programmatic element/attribute names or HTML comments, raw </textarea> reintroduction through Markdown passthrough, or preserved <style>/<meta http-equiv=refresh>/<base href> tags in custom policies. Most custom-policy issues do not affect the default sanitize=True configuration; they primarily affect helper APIs, programmatic DOM construction, html_passthrough=True, and custom policies/transform pipelines.

The advisory is available at github.com. This vulnerability was named CVE-2026-5388 since 04/01/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. Technical details are known, but there is no available exploit. This vulnerability is assigned to T1055 by the MITRE ATT&CK project.

Upgrading to version 1.15.0 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at CNNVD (CNNVD-2026-88910841). If you want to get best quality of vulnerability data, you may have to visit VulDB.

Productinfo

Vendor

• EmilStenstrom

Name

• justhtml

Version

• 1.0
• 1.1
• 1.2
• 1.3
• 1.4
• 1.5
• 1.6
• 1.7
• 1.8
• 1.9
• 1.10
• 1.11
• 1.12
• 1.13
• 1.14

Website

• Product: https://github.com/EmilStenstrom/justhtml/

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If you want to get best quality of vulnerability data, you may have to visit VulDB.

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