{"id":"CVE-2026-91187","summary":"Improper Verification of Cryptographic Signature in dashbit nimble_zta Cloudflare strategy","details":"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.\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.","aliases":["EEF-CVE-2026-91187","GHSA-rj24-g8cc-g7g2"],"modified":"2026-09-26T03:47:14.896050470Z","published":"2026-09-24T13:20:52.974Z","database_specific":{"cwe_ids":["CWE-347"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/91xxx/CVE-2026-91187.json","unresolved_ranges":[{"extracted_events":[{"introduced":"bc004b70985ae5763901baab3a4e204047899768"},{"fixed":"6458fd18a5ba41166d4973214c519e98fe05b72d"}],"source":"AFFECTED_FIELD"}],"cna_assigner":"EEF"},"references":[{"type":"WEB","url":"https://cna.erlef.org/cves/CVE-2026-91187.html"},{"type":"WEB","url":"https://github.com"},{"type":"WEB","url":"https://osv.dev/vulnerability/EEF-CVE-2026-91187"},{"type":"WEB","url":"https://repo.hex.pm"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/91xxx/CVE-2026-91187.json"},{"type":"ADVISORY","url":"https://github.com/dashbitco/nimble_zta/security/advisories/GHSA-rj24-g8cc-g7g2"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-91187"},{"type":"FIX","url":"https://github.com/dashbitco/nimble_zta/commit/6458fd18a5ba41166d4973214c519e98fe05b72d"},{"type":"FIX","url":"https://github.com/dashbitco/nimble_zta/commit/bc004b70985ae5763901baab3a4e204047899768"},{"type":"PACKAGE","url":"https://github.com/dashbitco/nimble_zta"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/dashbitco/nimble_zta","events":[{"introduced":"c1a084dd5ebe58bebfccb7bb8773f6dc280885bd"},{"fixed":"d515550552873410849ea208fd193e27f00058ad"},{"fixed":"6458fd18a5ba41166d4973214c519e98fe05b72d"},{"fixed":"bc004b70985ae5763901baab3a4e204047899768"}],"database_specific":{"extracted_events":[{"introduced":"0.1.2"},{"fixed":"0.1.3"}],"source":["DESCRIPTION","REFERENCES"]}}],"versions":["v0.1.2"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-91187.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"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"}]}