CVE-2026-91187

9.3 CRITICAL 0.3% exploit odds Fix listed Crypto

What it is

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.

At a glance

Exploitability: Can be exploited over the network without logging in. High risk of data exposure.
Exploit odds: 0.3% chance of exploitation in the next 30 days (EPSS).
Fix: A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

2026-09-15 15:30 UTC ReservedThe CVE id was reserved by its CNA
2026-09-24 14:18 UTC PublishedDisclosed publicly on CVE.org and NVD
2026-09-24 19:39 UTC Last updatedMost recent change to the record

Why it ranks here

Exploited in the wild: no, CISA does not list it.
Exploit odds: 0.3% in the next 30 days (EPSS).
Severity: 9.3 CRITICAL (CVSS).
Fix: a patch or advisory is linked.

Details

Published: 2026-09-24 14:18 UTC
Last modified: 2026-09-24 19:39 UTC
Exploit probability: 0.3% · EPSS, next 30 days
Weakness: CWE-347
Record status: Deferred

Attack profile CVSS 4.0 · 9.3

Attack vector: Network
Complexity: Low
Attack requirements: None
Privileges needed: None
User interaction: None
Confidentiality: High
Integrity: None
Availability: None

Raw vector

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

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2026-91187.md and follow it. Check whether this project is affected by CVE-2026-91187. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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Fix and advisories

References

NVD record · CVE.org record