Path Traversal in Ruby on Rails Action View (CVE‑2019‑5418) Enables File Disclosure
What It Is — Ruby on Rails’ Action View component mishandles specially‑crafted Accept headers combined with render file: calls, allowing an attacker to traverse directories and render arbitrary files from the server’s filesystem.
Exploitability — Publicly disclosed; proof‑of‑concept code exists; CVSS v3.1 base score 7.5 (High). No known active exploit campaigns, but the vulnerability is trivial to trigger on unpatched installations.
Affected Products — Ruby on Rails (all versions prior to 5.2.3, 6.0.0‑rc1).
Why It Matters for Trust & Control Assurance
- Access‑control hygiene – The flaw bypasses normal file‑access controls, highlighting the need for strict validation of user‑supplied paths and headers.
- Continuous evidence – Detecting unauthorized file reads requires logging of render calls and file‑access events, feeding into a defensible audit trail.
- Framework alignment – Remediating this issue satisfies the Access Control control objective on the Verisq Common Framework, which maps to many standards (e.g., NIST CSF 2.0 Identify‑Asset Management).
Recommended Actions
- Upgrade Rails to 5.2.3 or later (or the latest 6.x release).
- Review code for any custom
render file:usage and enforce whitelist‑based path validation. - Enable detailed logging for Action View rendering and monitor for anomalous file‑access patterns.
- Conduct a rapid control‑mapping exercise to confirm that the “Access Control – File Integrity” objective is evidenced in your compliance artifacts.
Source: CISA KEV – CVE‑2019‑5418