CVE-2026-91187 — Improper Verification of Cryptographic Signature in dashbit nimble_zta Cloudflare strategy
Improper Verification of Cryptographic Signature vulnerability in dashbit nimble_zta allows an unauthenticated remote attacker to authenticate as an arbitrary Cloudflare service…
Published: 2026-09-24 · CVSS: 9.3 · CVSS 4.0
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.
Source: CVE Program · Revision 8b16575c39f1e1810c5e863010da073d2d3285e7