CVE-2026-91187
Improper Verification of Cryptographic Signature in dashbit nimble_zta Cloudflare strategy
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.
INFO
Published Date :
Sept. 24, 2026, 2:18 p.m.
Last Modified :
Sept. 24, 2026, 7:39 p.m.
Remotely Exploit :
Yes !
Source :
6b3ad84c-e1a6-4bf7-a703-f496b71e49db
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 4.0 | CRITICAL | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db | ||||
| CVSS 4.0 | CRITICAL | 6b3ad84c-e1a6-4bf7-a703-f496b71e49db |
Solution
- Update the nimble_zta library to version 0.1.3 or later.
- Verify cryptographic signature validation logic.
- Ensure JWT verification checks are robust.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-91187.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-91187 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-91187
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-91187 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-91187 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
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CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Sep. 24, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-91187', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'yes'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-09-24T14:43:06.738544Z'} -
New CVE Received by 6b3ad84c-e1a6-4bf7-a703-f496b71e49db
Sep. 24, 2026
Action Type Old Value New Value Added 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. Added CVSS V4.0 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 Added CWE CWE-347 Added Affected New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/91xxx/CVE-2026-91187.json">CVE-2026-91187</a> Added Reference https://cna.erlef.org/cves/CVE-2026-91187.html Added Reference https://github.com/dashbitco/nimble_zta/commit/6458fd18a5ba41166d4973214c519e98fe05b72d Added Reference https://github.com/dashbitco/nimble_zta/commit/bc004b70985ae5763901baab3a4e204047899768 Added Reference https://github.com/dashbitco/nimble_zta/security/advisories/GHSA-rj24-g8cc-g7g2 Added Reference https://osv.dev/vulnerability/EEF-CVE-2026-91187