{"containers":{"adp":[{"metrics":[{"other":{"content":{"id":"CVE-2026-91187","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","timestamp":"2026-09-24T14:43:06.738544Z","version":"2.0.3"},"type":"ssvc"}}],"providerMetadata":{"dateUpdated":"2026-09-24T14:47:30.520Z","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","shortName":"CISA-ADP"},"title":"CISA ADP Vulnrichment"}],"cna":{"affected":[{"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:dashbit:nimble_zta:*:*:*:*:*:*:*:*"],"defaultStatus":"unaffected","modules":["'Elixir.NimbleZTA.Cloudflare'"],"packageName":"nimble_zta","packageURL":"pkg:hex/nimble_zta","product":"nimble_zta","programFiles":["lib/nimble_zta/cloudflare.ex"],"programRoutines":[{"name":"'Elixir.NimbleZTA.Cloudflare':authenticate/3"},{"name":"'Elixir.NimbleZTA.Cloudflare':verify_token/2"}],"repo":"https://github.com/dashbitco/nimble_zta","vendor":"dashbit","versions":[{"lessThan":"0.1.3","status":"affected","version":"0.1.2","versionType":"semver"}]},{"collectionURL":"https://github.com","cpes":["cpe:2.3:a:dashbit:nimble_zta:*:*:*:*:*:*:*:*"],"defaultStatus":"unaffected","modules":["'Elixir.NimbleZTA.Cloudflare'"],"packageName":"dashbitco/nimble_zta","packageURL":"pkg:github/dashbitco/nimble_zta","product":"nimble_zta","programFiles":["lib/nimble_zta/cloudflare.ex"],"programRoutines":[{"name":"'Elixir.NimbleZTA.Cloudflare':authenticate/3"},{"name":"'Elixir.NimbleZTA.Cloudflare':verify_token/2"}],"repo":"https://github.com/dashbitco/nimble_zta","vendor":"dashbit","versions":[{"lessThan":"6458fd18a5ba41166d4973214c519e98fe05b72d","status":"affected","version":"bc004b70985ae5763901baab3a4e204047899768","versionType":"git"}]}],"configurations":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"

The application must add NimbleZTA.Cloudflare to its supervision tree and authenticate requests through it.

"},{"base64":false,"type":"text/markdown","value":"The application must add `NimbleZTA.Cloudflare` to its supervision tree and authenticate requests through it."}],"value":"The application must add NimbleZTA.Cloudflare to its supervision tree and authenticate requests through it."}],"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:a:dashbit:nimble_zta:*:*:*:*:*:*:*:*","versionEndExcluding":"0.1.3","versionStartIncluding":"0.1.2","vulnerable":true}],"negate":false,"operator":"OR"}],"operator":"AND"}],"credits":[{"lang":"en","type":"finder","value":"Kazlu"},{"lang":"en","type":"remediation developer","value":"José Valim / Dashbit"},{"lang":"en","type":"coordinator","value":"Jonatan Männchen / EEF"}],"dateAssigned":"2026-09-24T09:09:36.000Z","descriptions":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"

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

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.

\n

This issue affects nimble_zta: from 0.1.2 before 0.1.3.

"},{"base64":false,"type":"text/markdown","value":"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\n`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.\n\nThis issue affects nimble_zta: from 0.1.2 before 0.1.3."}],"value":"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."}],"impacts":[{"capecId":"CAPEC-475","descriptions":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"

The attacker authenticates as an arbitrary Cloudflare service token without holding the Cloudflare signing key. The application receives the client_id and the claims of the forged token as the authenticated identity, so the attacker gets the access that the application grants to that service token.

"},{"base64":false,"type":"text/markdown","value":"The attacker authenticates as an arbitrary Cloudflare service token without holding the Cloudflare signing key. The application receives the `client_id` and the claims of the forged token as the authenticated identity, so the attacker gets the access that the application grants to that service token."}],"value":"The attacker authenticates as an arbitrary Cloudflare service token without holding the Cloudflare signing key. The application receives the client_id and the claims of the forged token as the authenticated identity, so the attacker gets the access that the application grants to that service token."}]}],"metrics":[{"cvssV4_0":{"Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","Safety":"NOT_DEFINED","attackComplexity":"LOW","attackRequirements":"NONE","attackVector":"NETWORK","baseScore":9.3,"baseSeverity":"CRITICAL","privilegesRequired":"NONE","providerUrgency":"NOT_DEFINED","subAvailabilityImpact":"NONE","subConfidentialityImpact":"HIGH","subIntegrityImpact":"HIGH","userInteraction":"NONE","valueDensity":"NOT_DEFINED","vectorString":"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","version":"4.0","vulnAvailabilityImpact":"NONE","vulnConfidentialityImpact":"HIGH","vulnIntegrityImpact":"NONE","vulnerabilityResponseEffort":"NOT_DEFINED"},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-347","description":"CWE-347 Improper Verification of Cryptographic Signature","lang":"en","type":"CWE"}]}],"providerMetadata":{"dateUpdated":"2026-09-24T13:20:52.974Z","orgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","shortName":"EEF"},"references":[{"name":"GitHub Advisory","tags":["related","vendor-advisory"],"url":"https://github.com/dashbitco/nimble_zta/security/advisories/GHSA-rj24-g8cc-g7g2"},{"name":"EEF CNA record for CVE-2026-91187","tags":["related"],"url":"https://cna.erlef.org/cves/CVE-2026-91187.html"},{"name":"OSV record EEF-CVE-2026-91187","tags":["related"],"url":"https://osv.dev/vulnerability/EEF-CVE-2026-91187"},{"name":"Introducing commit bc004b7 in dashbitco/nimble_zta","tags":["related"],"url":"https://github.com/dashbitco/nimble_zta/commit/bc004b70985ae5763901baab3a4e204047899768"},{"name":"Fix commit 6458fd1 in dashbitco/nimble_zta","tags":["patch"],"url":"https://github.com/dashbitco/nimble_zta/commit/6458fd18a5ba41166d4973214c519e98fe05b72d"}],"source":{"discovery":"EXTERNAL"},"title":"Improper Verification of Cryptographic Signature in dashbit nimble_zta Cloudflare strategy","workarounds":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"

Disable the Cloudflare authentication strategy.

\n

To keep the user identity strategy available, reject the service token requests yourself. Examine each request before you call NimbleZTA.Cloudflare.authenticate/3, and reject it if its JWT carries the common_name claim and the type claim.

"},{"base64":false,"type":"text/markdown","value":"Disable the Cloudflare authentication strategy.\n\nTo keep the user identity strategy available, reject the service token requests yourself. Examine each request before you call `NimbleZTA.Cloudflare.authenticate/3`, and reject it if its JWT carries the `common_name` claim and the `type` claim."}],"value":"Disable the Cloudflare authentication strategy.\n\nTo keep the user identity strategy available, reject the service token requests yourself. Examine each request before you call NimbleZTA.Cloudflare.authenticate/3, and reject it if its JWT carries the common_name claim and the type claim."}],"x_proofOfConcept":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"
    \n
  1. Build a JWT payload that carries the aud, common_name, exp, iat, iss, sub and type claims. Use the iss the application expects, set exp to a future timestamp, and set common_name to the service token to impersonate.
    2. \n
  2. Append any signature segment. The segment must be present, because JOSE.JWT.verify/2 needs three segments to parse the token. The signature does not need to verify against the Cloudflare keys.
    3. \n
  3. Send a request to the application with the forged JWT in the cf-access-jwt-assertion header.
    4. \n
  4. NimbleZTA.Cloudflare.authenticate/3 returns the claims of the forged token as the authenticated identity, with the strategy field set to service_token.
    5. \n
"},{"base64":false,"type":"text/markdown","value":"1. Build a JWT payload that carries the `aud`, `common_name`, `exp`, `iat`, `iss`, `sub` and `type` claims. Use the `iss` the application expects, set `exp` to a future timestamp, and set `common_name` to the service token to impersonate.\n2. Append any signature segment. The segment must be present, because `JOSE.JWT.verify/2` needs three segments to parse the token. The signature does not need to verify against the Cloudflare keys.\n3. Send a request to the application with the forged JWT in the `cf-access-jwt-assertion` header.\n4. `NimbleZTA.Cloudflare.authenticate/3` returns the claims of the forged token as the authenticated identity, with the `strategy` field set to `service_token`."}],"value":"* Build a JWT payload that carries the aud, common_name, exp, iat, iss, sub and type claims. Use the iss the application expects, set exp to a future timestamp, and set common_name to the service token to impersonate.\n* Append any signature segment. The segment must be present, because JOSE.JWT.verify/2 needs three segments to parse the token. The signature does not need to verify against the Cloudflare keys.\n* Send a request to the application with the forged JWT in the cf-access-jwt-assertion header.\n* NimbleZTA.Cloudflare.authenticate/3 returns the claims of the forged token as the authenticated identity, with the strategy field set to service_token."}]}},"cveMetadata":{"assignerOrgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","assignerShortName":"EEF","cveId":"CVE-2026-91187","datePublished":"2026-09-24T13:20:52.974Z","dateReserved":"2026-09-15T15:30:01.892Z","dateUpdated":"2026-09-24T14:47:30.520Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"}