---
id: CVE-2026-91187
title: >-
  Improper Verification of Cryptographic Signature vulnerability in dashbit
  nimble_zta allows an unauthenticated remote attacker to authenticate as an
  arbitrary Cloudflare service token
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 authent…
severity: critical
cvss: 9.3
cvssVector: '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'
cwe:
  - CWE-347
vendor: dashbit
product: nimble_zta
affected:
  - nimble_zta >= 0.1.2 < 0.1.3
  - >-
    dashbitco/nimble_zta >= bc004b70985ae5763901baab3a4e204047899768 <
    6458fd18a5ba41166d4973214c519e98fe05b72d
published: '2026-09-24'
updated: '2026-09-24'
sourceUpdated: '2026-09-24T19:39:45.600'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-91187'
references:
  - url: 'https://cna.erlef.org/cves/CVE-2026-91187.html'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/dashbitco/nimble_zta/commit/6458fd18a5ba41166d4973214c519e98fe05b72d
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/dashbitco/nimble_zta/commit/bc004b70985ae5763901baab3a4e204047899768
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: >-
      https://github.com/dashbitco/nimble_zta/security/advisories/GHSA-rj24-g8cc-g7g2
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
  - url: 'https://osv.dev/vulnerability/EEF-CVE-2026-91187'
    label: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
tags:
  - nvd
  - cve.org
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-09-24T14:43:06.738544Z'
cvssSource: cna
ingestedAt: '2026-09-24T13:43:25.676Z'
epss: 0.00303
epssPercentile: 0.20574
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.