Vulnerability · Published Sep 24, 2026 · Assigned by EEF

CVE-2026-91187Improper Verification of Cryptographic Signature in dashbit nimble_zta Cloudflare strategy

Critical 9.3

In plain English

A critical-severity security flaw in nimble_zta from dashbit. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 23% of all known vulnerabilities).

Severity (CVSS 4.0)9.3Critical

Exploit odds (30 days)0.3%top 76.7% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Ubuntu:22.04:LTS	dash	no fix listed	UBUNTU-CVE-2026-91187
Ubuntu:24.04:LTS	dash	no fix listed	UBUNTU-CVE-2026-91187
Ubuntu:26.04:LTS	dash	no fix listed	UBUNTU-CVE-2026-91187

Affected products (as reported)

Vendor	Product	Versions
dashbit	nimble_zta	0.1.2 – before 0.1.3
dashbit	nimble_zta	bc004b70985ae5763901baab3a4e204047899768 – before 6458fd18a5ba41166d4973214c519e98fe05b72d

Weakness: CWE-347 · 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

References

GitHub Advisory related, vendor-advisory
EEF CNA record for CVE-2026-91187 related
OSV record EEF-CVE-2026-91187 related
Introducing commit bc004b7 in dashbitco/nimble_zta related
Fix commit 6458fd1 in dashbitco/nimble_zta patch