CVE-2020-5217: Directive injection when using dynamic overrides with user input in RubyGems secure_headers

Severity: medium (CVSS 5.8 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.8% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2020-01-23 · updated 2026-06-17
Weakness: CWE-95

Description

In Secure Headers (RubyGem secure_headers), a directive injection vulnerability is present in versions before 3.8.0, 5.1.0, and 6.2.0. If user-supplied input was passed into append/override_content_security_policy_directives, a semicolon could be injected leading to directive injection. This could be used to e.g. override a script-src directive. Duplicate directives are ignored and the first one wins. The directives in secure_headers are sorted alphabetically so they pretty much all come before script-src. A previously undefined directive would receive a value even if SecureHeaders::OPT_OUT was supplied. The fixed versions will silently convert the semicolons to spaces and emit a deprecation warning when this happens. This will result in innocuous browser console messages if being exploited/accidentally used. In future releases, we will raise application errors resulting in 500s. Depending on what major version you are using, the fixed versions are 6.2.0, 5.1.0, 3.8.0.

Affected products

Twitter secure_headers: before 3.8.0; from 5.0.0 before 5.1.0; from 6.0.0 before 6.2.0 — fixed in 3.8.0, 5.1.0, 6.2.0

How to fix

Upgrade to a fixed version: Twitter secure_headers 3.8.0, 5.1.0, 6.2.0. Check the vendor advisory for mitigations.

References

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