CVE-2026-54163 secure_headers: CSP directive injection via sandbox, plugin_types, and report_to when given untrusted input
Attackers can inject CSP directives to enable XSS or exfiltrate reports via untrusted input in secure_headers library APIs.
- 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-2026-54163?
CVE-2026-54163 is a medium-severity cross-site scripting vulnerability in github secure_headers, published on 17 Jul 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
secure_headers manages application of security headers with many safe defaults. Prior to 7.3.0, secure_headers builds the Content-Security-Policy value by stitching directives with ; separators, and build_sandbox_list_directive, build_media_type_list_directive, and build_report_to_directive interpolate caller-supplied strings without scrubbing ;, \r, or \n. When untrusted input reaches SecureHeaders.override_content_security_policy_directives or append APIs for :sandbox, :plugin_types, or :report_to, an attacker can inject a CSP directive such as script-src 'unsafe-inline' * before the legitimate script-src, enabling XSS reachability through these sinks or CSP report exfiltration. This issue is fixed in version 7.3.0.
Which versions are affected by CVE-2026-54163?
2 open source packages ship an affected version, including secure_headers.
| Package | Affected | Fixed in |
|---|---|---|
secure_headers RubyGems | All versions | 7.3.0 |
secure_headers RubyGems | All versions | 7.3.0 |
How do I fix CVE-2026-54163?
Upgrade secure_headers to 7.3.0 or later.
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-2026-54163 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-54163 exists.
Sources
Also known as DEBIAN-CVE-2026-54163, GHSA-rqq5-2gf9-4w4q, UBUNTU-CVE-2026-54163.