Improper Verification of Cryptographic Signature in dashbit nimble_zta Cloudflare strategy
Summary
| CVE | CVE-2026-91187 |
|---|---|
| State | PUBLISHED |
| Assigner | EEF |
| Source Priority | CVE Program / NVD first with legacy fallback |
| Published | 2026-09-24 14:18:18 UTC |
| Updated | 2026-09-24 19:39:45 UTC |
| Description | 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. |
Risk And Classification
Primary CVSS: v4.0 9.3 CRITICAL from 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
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
Problem Types: CWE-347 | CWE-347 CWE-347 Improper Verification of Cryptographic Signature
| Version | Source | Type | Score | Severity | Vector |
|---|---|---|---|---|---|
| 4.0 | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | Secondary | 9.3 | CRITICAL | 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/C... |
| 4.0 | CNA | CVSS | 9.3 | CRITICAL | 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 |
CVSS v4.0 Breakdown
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
Vendor Declared Affected Products
| Source | Vendor | Product | Version | Platforms |
|---|---|---|---|---|
| CNA | Dashbit | Nimble Zta | affected 0.1.2 0.1.3 semver | Not specified |
| CNA | Dashbit | Nimble Zta | affected bc004b70985ae5763901baab3a4e204047899768 6458fd18a5ba41166d4973214c519e98fe05b72d git | Not specified |
References
| Reference | Source | Link | Tags |
|---|---|---|---|
| github.com/dashbitco/nimble_zta/security/advisories/GHSA-rj24-g8cc-g7g2 | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | github.com | |
| github.com/dashbitco/nimble_zta/commit/bc004b70985ae5763901baab3a4e20404... | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | github.com | |
| github.com/dashbitco/nimble_zta/commit/6458fd18a5ba41166d4973214c519e98f... | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | github.com | |
| cna.erlef.org/cves/CVE-2026-91187.html | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | cna.erlef.org | |
| osv.dev/vulnerability/EEF-CVE-2026-91187 | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | osv.dev | |
| CVE Program record | CVE.ORG | www.cve.org | canonical |
| NVD vulnerability detail | NVD | nvd.nist.gov | canonical, analysis |
Vendor Comments And Credit
Discovery Credit
CNA: Kazlu (en)
CNA: José Valim / Dashbit (en)
CNA: Jonatan Männchen / EEF (en)
Additional Advisory Data
Workarounds
CNA: Disable the Cloudflare authentication strategy. 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.