{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-91187", "assignerOrgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "state": "PUBLISHED", "assignerShortName": "EEF", "dateReserved": "2026-09-15T15:30:01.892Z", "datePublished": "2026-09-24T13:20:52.974Z", "dateUpdated": "2026-09-24T14:47:30.520Z" }, "containers": { "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": { "orgId": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db", "shortName": "EEF", "dateUpdated": "2026-09-24T13:20:52.974Z" }, "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." } ] }, "adp": [ { "metrics": [ { "other": { "type": "ssvc", "content": { "timestamp": "2026-09-24T14:43:06.738544Z", "id": "CVE-2026-91187", "options": [ { "Exploitation": "none" }, { "Automatable": "yes" }, { "Technical Impact": "partial" } ], "role": "CISA Coordinator", "version": "2.0.3" } } } ], "title": "CISA ADP Vulnrichment", "providerMetadata": { "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-09-24T14:47:30.520Z" } } ] } }