{"id":"CVE-2026-91187","title":"Improper Verification of Cryptographic Signature vulnerability in dashbit nimble_zta allows an unauthenticated remote attacker to authenticate as an arbitrary Cloudflare service token","summary":"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 authent…","severity":"critical","cvss":9.3,"cvssVector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:H/SI:H/SA:N","cwe":["CWE-347"],"vendor":"dashbit","product":"nimble_zta","affected":["nimble_zta >= 0.1.2 < 0.1.3","dashbitco/nimble_zta >= bc004b70985ae5763901baab3a4e204047899768 < 6458fd18a5ba41166d4973214c519e98fe05b72d"],"published":"2026-09-24","updated":"2026-09-24","sourceUpdated":"2026-09-24T19:39:45.600","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-91187","references":[{"url":"https://cna.erlef.org/cves/CVE-2026-91187.html","label":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"},{"url":"https://github.com/dashbitco/nimble_zta/commit/6458fd18a5ba41166d4973214c519e98fe05b72d","label":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"},{"url":"https://github.com/dashbitco/nimble_zta/commit/bc004b70985ae5763901baab3a4e204047899768","label":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"},{"url":"https://github.com/dashbitco/nimble_zta/security/advisories/GHSA-rj24-g8cc-g7g2","label":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-91187","label":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db"}],"tags":["nvd","cve.org"],"ssvc":{"exploitation":"none","automatable":"yes","technicalImpact":"partial","timestamp":"2026-09-24T14:43:06.738544Z"},"cvssSource":"cna","ingestedAt":"2026-09-24T13:43:25.676Z","slug":"CVE-2026-91187","body":"## Overview\n\nImproper 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.\n\nverify_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.\n\nThis issue affects nimble_zta: from 0.1.2 before 0.1.3.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"midnight","depthScore":51,"depthScoreParts":{"impact":51.2,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}