CVE-2026-91187 json
Improper Verification of Cryptographic Signature in dashbit nimble_zta Cloudflare strategy
published 2026-09-24 45 d ago modified 2026-09-24 45 d ago also EEF-CVE-2026-91187 , GHSA-rj24-g8cc-g7g2 , EUVD-2026-85871
- cvss
- 9.3
- version 4.0, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.3%
- EPSS 0.3% chance of exploitation in 30 days, percentile 23%
- public exploits
- 0
- none known
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.
Patch / fix
- hex nimble_zta 0.1.3
- dashbit nimble_zta 0.1.3
CISA SSVC
- Exploitation
- none
- Automatable
- yes
- Technical impact
- partial
- Assessed
- 45 d ago
Exploit prediction
0.30% chance of exploitation in the next 30 days, higher than 23% of all scored CVEs (FIRST EPSS, 2026-11-08).
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 4.0 | 9.3 | 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 |
| CNA | 4.0 | 9.3 | 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X |
Affected packages
| ecosystem | package | affected | fixed in |
|---|---|---|---|
| hex | nimble_zta | >=0.1.2, <0.1.3 |
0.1.3 |
Affected products
- dashbit nimble_zta
Classification
- Weakness
-
- CWE-347 Improper Verification of Cryptographic Signature
References
-
github.com
/dashbitco/nimble_zta/commit/bc004b70985ae5763901baab3a4e204047899768
related, web
-
github.com
/dashbitco/nimble_zta/commit/6458fd18a5ba41166d4973214c519e98fe05b72d
patch
-
github.com
/dashbitco/nimble_zta/security/advisories/GHSA-rj24-g8cc-g7g2
related, vendor-advisory, advisory
-
cna.erlef.org
/cves/CVE-2026-91187.html
related, web
-
osv.dev
/vulnerability/EEF-CVE-2026-91187
related
-
hex.pm
/packages/nimble_zta
package
Sources
- CVE List CVE-2026-91187
- NVD CVE-2026-91187
- OSV EEF-CVE-2026-91187
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