CVE-2026-91187

Reference list NVD curates from the CNA record, vendor advisories, and third-party reports. The tag chips below are NVD's analyst-assigned categories.

• https://cna.erlef.org/cves/CVE-2026-91187.html 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
• https://github.com/dashbitco/nimble_zta/commit/6458fd18a5ba41166d4973214c519e98fe05b72d 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
• https://github.com/dashbitco/nimble_zta/commit/bc004b70985ae5763901baab3a4e204047899768 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
• https://github.com/dashbitco/nimble_zta/security/advisories/GHSA-rj24-g8cc-g7g2 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
• https://osv.dev/vulnerability/EEF-CVE-2026-91187 6b3ad84c-e1a6-4bf7-a703-f496b71e49db

The full cvelistV5 record. Download as CVE-2026-91187.json.

{
  "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": "<p>The application must add <code>NimbleZTA.Cloudflare</code> to its supervision tree and authenticate requests through it.</p>"
            },
            {
              "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": "Jos\u00e9 Valim / Dashbit"
        },
        {
          "lang": "en",
          "type": "coordinator",
          "value": "Jonatan M\u00e4nnchen / EEF"
        }
      ],
      "dateAssigned": "2026-09-24T09:09:36.000Z",
      "descriptions": [
        {
          "lang": "en",
          "supportingMedia": [
            {
              "base64": false,
              "type": "text/html",
              "value": "<p>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.</p>\n<p><code>verify_token/2</code> in <code>lib/nimble_zta/cloudflare.ex</code> matches the result of <code>JOSE.JWT.verify/2</code> against <code>{_, token, _s}</code>, which discards the boolean verification result and returns the decoded token after a failed signature check. The attacker sends a forged JWT in the <code>cf-access-jwt-assertion</code> header, carrying the expected <code>iss</code> claim and the seven service token claims. <code>verify_iss/2</code> reads the <code>iss</code> claim from the forged token, so it rejects nothing, and the service token path then returns those claims as the authenticated identity.</p>\n<p>This issue affects nimble_zta: from 0.1.2 before 0.1.3.</p>"
            },
            {
              "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": "<p>The attacker authenticates as an arbitrary Cloudflare service token without holding the Cloudflare signing key. The application receives the <code>client_id</code> 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.</p>"
                },
                {
                  "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": "<p>Disable the Cloudflare authentication strategy.</p>\n<p>To keep the user identity strategy available, reject the service token requests yourself. Examine each request before you call <code>NimbleZTA.Cloudflare.authenticate/3</code>, and reject it if its JWT carries the <code>common_name</code> claim and the <code>type</code> claim.</p>"
            },
            {
              "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": "<ol>\n<li>Build a JWT payload that carries the <code>aud</code>, <code>common_name</code>, <code>exp</code>, <code>iat</code>, <code>iss</code>, <code>sub</code> and <code>type</code> claims. Use the <code>iss</code> the application expects, set <code>exp</code> to a future timestamp, and set <code>common_name</code> to the service token to impersonate.</li>\n<li>Append any signature segment. The segment must be present, because <code>JOSE.JWT.verify/2</code> needs three segments to parse the token. The signature does not need to verify against the Cloudflare keys.</li>\n<li>Send a request to the application with the forged JWT in the <code>cf-access-jwt-assertion</code> header.</li>\n<li><code>NimbleZTA.Cloudflare.authenticate/3</code> returns the claims of the forged token as the authenticated identity, with the <code>strategy</code> field set to <code>service_token</code>.</li>\n</ol>"
            },
            {
              "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"
}