Medium [CVE-2026-52846] Client-side Cross-Site Scripting (XSS) due to incomplete HTML tag stripping
This medium-severity Red Hat Linux advisory covers CVE-2026-52846.
Aggregated and source-linked by VulniPulse. Data sources, validation and limitations.
VulniPulse record published
Summary
Caddy is an extensible server platform that uses TLS by default. Prior to 2.11.4, Caddy’s stripHTML template function cannot reliably remove all HTML tags from input strings.
Certain malformed HTML, such as img src=x onerror=alert()>, can bypass the tag-stripping logic, potentially leaving dangerous content in the output if it is later rendered as HTML. This may allow client-side XSS in cases where untrusted strings are rendered unsafely.
This vulnerability is fixed in 2.11.4. This oversight allows dangerous content to remain in the output, which, if subsequently rendered as HTML, can lead to client-side Cross-Site Scripting (XSS).
A remote attacker could exploit this by providing specially crafted input, potentially executing malicious scripts in a user's browser. Caddy's stripHTML template function fails to reliably strip malformed HTML, which can lead to client-side XSS if untrusted input is rendered through Caddy's `templates` directive.
Exploitation requires the `templates` directive to be enabled in a Caddyfile with a template that calls stripHTML on untrusted input; Caddy deployments that only use `file_server` for static asset serving never reach the vulnerable function.
Is CVE-2026-52846 exploited?
No exploitation is reported in the sources VulniPulse tracks: CVE-2026-52846 is not in the CISA KEV catalog (checked ) and this advisory does not report exploitation. That is not proof the vulnerability cannot be exploited.
How do I fix CVE-2026-52846?
Upgrade to a fixed release named by Red Hat:
- 2.11.4
Confirm against the vendor advisory before you patch.
- < 2.11.4
Official advisory · high-confidence parse· fetched 14 days ago·verify at source
Mitigation checklist
- Users who have enabled Caddy's `templates` directive with untrusted input passed through the stripHTML function should upgrade to Caddy 2.11.4 or later, or disable the `templates` directive if not required.
Official advisory · high-confidence parse· fetched 14 days ago·verify at source
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