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9.3
CVE-2026-91187: dashbit nimble_zta lets attacker forge Cloudflare token
CVE-2026-91187 · published 17 days ago
Summary
The dashbit nimble_zta library used for Cloudflare Zero Trust authentication can be tricked into accepting a fake token. An attacker can send a crafted token and appear as any Cloudflare service, gaining unauthorized access. Upgrade to version 0.1.3 or later to fix the issue.
What to do
- Update dashbit nimble_zta to version 0.1.3.
- Update nimble_zta to version 0.1.3.
Affected software
| Ecosystem | Vendor | Product | Affected versions |
|---|---|---|---|
| – | dashbit | nimble_zta |
< 0.1.3 < 6458fd18a5ba41166d4973214c519e98fe05b72d |
| Hex | dashbit | nimble_zta |
>= 0.1.2, < 0.1.3 Fix: upgrade to 0.1.3
|
| Ubuntu:14.04:LTS | canonical | dash | All versions |
| Hex | – | nimble_zta |
>= 0.1.2, < 0.1.3 Fix: upgrade to 0.1.3
|
Original advisory text
Improper Verification of Cryptographic Signature in dashbit nimble_zta Cloudflare strategy
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.
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.
References
- https://osv.dev/vulnerability/EEF-CVE-2026-91187
- https://github.com/dashbitco/nimble_zta/security/advisories/GHSA-rj24-g8cc-g7g2
- https://cna.erlef.org/cves/CVE-2026-91187.html
- https://github.com/dashbitco/nimble_zta/commit/bc004b70985ae5763901baab3a4e20404...
- https://ubuntu.com/security/CVE-2026-91187 Third Party Advisory
- https://www.cve.org/CVERecord?id=CVE-2026-91187 Third Party Advisory
- https://github.com URL
- https://repo.hex.pm URL
- https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/91xxx/CVE-2026-91187... Vendor Advisory
- https://nvd.nist.gov/vuln/detail/CVE-2026-91187 Vendor Advisory
- https://github.com/dashbitco/nimble_zta Product
- https://github.com/dashbitco/nimble_zta/commit/6458fd18a5ba41166d4973214c519e98f...
- https://hex.pm/packages/nimble_zta Product
Internet-facing
14 days
Internal
60 days
- Not known to be exploited
- Can be exploited automatically
- Gives an attacker partial control
Severity
9.3
Critical
Type
CWE-347Improper Verification of Cryptographic Signature
Timeline
Published24 Sep 2026
Updated9 Oct 2026
First seen24 Sep 2026
Sources
CVE-2026-91187 · NVD
CVE-2026-91187 · MITRE
EEF-CVE-2026-91187 · OSV
GHSA-rj24-g8cc-g7g2 · GHSA
UBUNTU-CVE-2026-91187 · OSV
CVE-2026-91187 · OSV
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