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2 vulnerabilities by dashbit
CVE-2026-91187 (GCVE-0-2026-91187)
Vulnerability from nvd – Published: 2026-09-24 13:20 – Updated: 2026-09-24 14:47
VLAI
EPSS
VEX
Title
Improper Verification of Cryptographic Signature in dashbit nimble_zta Cloudflare strategy
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 authentication strategy are affected.
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.
This issue affects nimble_zta: from 0.1.2 before 0.1.3.
Severity
SSVC
Exploitation: none
Automatable: yes
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-24 14:43 UTC
CWE
- CWE-347 - Improper Verification of Cryptographic Signature
Assigner
References
5 references
| URL | Tags |
|---|---|
| https://github.com/dashbitco/nimble_zta/security/… | relatedvendor-advisory |
| https://cna.erlef.org/cves/CVE-2026-91187.html | related |
| https://osv.dev/vulnerability/EEF-CVE-2026-91187 | related |
| https://github.com/dashbitco/nimble_zta/commit/bc… | related |
| https://github.com/dashbitco/nimble_zta/commit/64… | patch |
Impacted products
2 products
| Vendor | Product | Version | |
|---|---|---|---|
| dashbit | nimble_zta |
Affected:
0.1.2 , < 0.1.3
(semver)
cpe:2.3:a:dashbit:nimble_zta:*:*:*:*:*:*:*:* |
|
| dashbit | nimble_zta |
Affected:
bc004b70985ae5763901baab3a4e204047899768 , < 6458fd18a5ba41166d4973214c519e98fe05b72d
(git)
cpe:2.3:a:dashbit:nimble_zta:*:*:*:*:*:*:*:* |
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CVE-2026-91187 (GCVE-0-2026-91187)
Vulnerability from cvelistv5 – Published: 2026-09-24 13:20 – Updated: 2026-09-24 14:47
VLAI
EPSS
VEX
Title
Improper Verification of Cryptographic Signature in dashbit nimble_zta Cloudflare strategy
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 authentication strategy are affected.
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.
This issue affects nimble_zta: from 0.1.2 before 0.1.3.
Severity
SSVC
Exploitation: none
Automatable: yes
Technical Impact: partial
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-24 14:43 UTC
CWE
- CWE-347 - Improper Verification of Cryptographic Signature
Assigner
References
5 references
| URL | Tags |
|---|---|
| https://github.com/dashbitco/nimble_zta/security/… | relatedvendor-advisory |
| https://cna.erlef.org/cves/CVE-2026-91187.html | related |
| https://osv.dev/vulnerability/EEF-CVE-2026-91187 | related |
| https://github.com/dashbitco/nimble_zta/commit/bc… | related |
| https://github.com/dashbitco/nimble_zta/commit/64… | patch |
Impacted products
2 products
| Vendor | Product | Version | |
|---|---|---|---|
| dashbit | nimble_zta |
Affected:
0.1.2 , < 0.1.3
(semver)
cpe:2.3:a:dashbit:nimble_zta:*:*:*:*:*:*:*:* |
|
| dashbit | nimble_zta |
Affected:
bc004b70985ae5763901baab3a4e204047899768 , < 6458fd18a5ba41166d4973214c519e98fe05b72d
(git)
cpe:2.3:a:dashbit:nimble_zta:*:*:*:*:*:*:*:* |
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"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": [
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"value": "\u003cp\u003eImproper 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.\u003c/p\u003e\n\u003cp\u003e\u003ccode\u003everify_token/2\u003c/code\u003e in \u003ccode\u003elib/nimble_zta/cloudflare.ex\u003c/code\u003e matches the result of \u003ccode\u003eJOSE.JWT.verify/2\u003c/code\u003e against \u003ccode\u003e{_, token, _s}\u003c/code\u003e, which discards the boolean verification result and returns the decoded token after a failed signature check. The attacker sends a forged JWT in the \u003ccode\u003ecf-access-jwt-assertion\u003c/code\u003e header, carrying the expected \u003ccode\u003eiss\u003c/code\u003e claim and the seven service token claims. \u003ccode\u003everify_iss/2\u003c/code\u003e reads the \u003ccode\u003eiss\u003c/code\u003e claim from the forged token, so it rejects nothing, and the service token path then returns those claims as the authenticated identity.\u003c/p\u003e\n\u003cp\u003eThis issue affects nimble_zta: from 0.1.2 before 0.1.3.\u003c/p\u003e"
},
{
"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": "\u003cp\u003eThe attacker authenticates as an arbitrary Cloudflare service token without holding the Cloudflare signing key. The application receives the \u003ccode\u003eclient_id\u003c/code\u003e 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.\u003c/p\u003e"
},
{
"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": "\u003cp\u003eDisable the Cloudflare authentication strategy.\u003c/p\u003e\n\u003cp\u003eTo keep the user identity strategy available, reject the service token requests yourself. Examine each request before you call \u003ccode\u003eNimbleZTA.Cloudflare.authenticate/3\u003c/code\u003e, and reject it if its JWT carries the \u003ccode\u003ecommon_name\u003c/code\u003e claim and the \u003ccode\u003etype\u003c/code\u003e claim.\u003c/p\u003e"
},
{
"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": "\u003col\u003e\n\u003cli\u003eBuild a JWT payload that carries the \u003ccode\u003eaud\u003c/code\u003e, \u003ccode\u003ecommon_name\u003c/code\u003e, \u003ccode\u003eexp\u003c/code\u003e, \u003ccode\u003eiat\u003c/code\u003e, \u003ccode\u003eiss\u003c/code\u003e, \u003ccode\u003esub\u003c/code\u003e and \u003ccode\u003etype\u003c/code\u003e claims. Use the \u003ccode\u003eiss\u003c/code\u003e the application expects, set \u003ccode\u003eexp\u003c/code\u003e to a future timestamp, and set \u003ccode\u003ecommon_name\u003c/code\u003e to the service token to impersonate.\u003c/li\u003e\n\u003cli\u003eAppend any signature segment. The segment must be present, because \u003ccode\u003eJOSE.JWT.verify/2\u003c/code\u003e needs three segments to parse the token. The signature does not need to verify against the Cloudflare keys.\u003c/li\u003e\n\u003cli\u003eSend a request to the application with the forged JWT in the \u003ccode\u003ecf-access-jwt-assertion\u003c/code\u003e header.\u003c/li\u003e\n\u003cli\u003e\u003ccode\u003eNimbleZTA.Cloudflare.authenticate/3\u003c/code\u003e returns the claims of the forged token as the authenticated identity, with the \u003ccode\u003estrategy\u003c/code\u003e field set to \u003ccode\u003eservice_token\u003c/code\u003e.\u003c/li\u003e\n\u003c/ol\u003e"
},
{
"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"
}