Vulnerability Description
Improper Verification of Cryptographic Signature vulnerability in dashbit nimble_zta allows an unauthenticated remote attacker to authenticate as an arbitrary Cloudflare service token. Applications using the Cloudflare Zero Trust authentication strategy are affected. verify_token/2 in lib/nimble_zta/cloudflare.ex matches the result of JOSE.JWT.verify/2 against {_, token, _s}, which discards the boolean verification result and returns the decoded token after a failed signature check. The attacker sends a forged JWT in the cf-access-jwt-assertion header, carrying the expected iss claim and the seven service token claims. verify_iss/2 reads the iss claim from the forged token, so it rejects nothing, and the service token path then returns those claims as the authenticated identity. This issue affects nimble_zta: from 0.1.2 before 0.1.3.
Related Weaknesses (CWE)
References
- https://cna.erlef.org/cves/CVE-2026-91187.html
- https://github.com/dashbitco/nimble_zta/commit/6458fd18a5ba41166d4973214c519e98f
- https://github.com/dashbitco/nimble_zta/commit/bc004b70985ae5763901baab3a4e20404
- https://github.com/dashbitco/nimble_zta/security/advisories/GHSA-rj24-g8cc-g7g2
- https://osv.dev/vulnerability/EEF-CVE-2026-91187
FAQ
What is CVE-2026-91187?
CVE-2026-91187 is a documented vulnerability. Improper Verification of Cryptographic Signature vulnerability in dashbit nimble_zta allows an unauthenticated remote attacker to authenticate as an arbitrary Cloudflare service token. Applications us...
How severe is CVE-2026-91187?
CVSS scoring is not yet available for CVE-2026-91187. Check NVD for updates.
Is there a patch for CVE-2026-91187?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.