CVE-2026-91187Network attack vector

Authentication bypass via discarded JWT verification result

Published Sep 24, 2026 · Updated Sep 24, 2026

Improper signature verification in Dashbit NimbleZTA 0.1.2 allows remote attackers to authenticate as arbitrary Cloudflare service tokens. Cloudflare.verify_token/2 treats every JOSE.JWT.verify/2 tuple as success, discarding its boolean result and accepting a forged JWT's decoded claims. Exploitation requires an application to enable the opt-in Cloudflare strategy; a crafted cf-access-jwt-assertion header then grants the service-token identity and its protected access.

CVSS severity9.2
Critical
EPSS probability0.30%
Next 30 days · Oct 19, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper signature verification in Dashbit NimbleZTA 0.1.2 allows remote attackers to authenticate as arbitrary Cloudflare service tokens. Cloudflare.verify_token/2 treats every JOSE.JWT.verify/2 tuple as success, discarding its boolean result and accepting a forged JWT's decoded claims. Exploitation requires an application to enable the opt-in Cloudflare strategy; a crafted cf-access-jwt-assertion header then grants the service-token identity and its protected access.

The record

CVE
CVE-2026-91187
Published
Sep 24, 2026
Updated
Sep 24, 2026
Vendor
Dashbit
Product
NimbleZTA
Classifications
CWE-347, T1550.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 24, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 24, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0.1.2 <0.1.3
  2. Affected versionversion=bc004b70985ae5763901baab3a4e204047899768 <6458fd18a5ba41166d4973214c519e98fe05b72d

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Dashbit · NimbleZTAversion=0.1.2 <0.1.3; version=bc004b70985ae5763901baab3a4e204047899768 <6458fd18a5ba41166d4973214c519e98fe05b72d

Published CVSS scores

9.2GitHub Security AdvisoryCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:H/SI:N/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Activity data is delayed. The latest report is Sep 28, 2026.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 22, 2026Sep 28, 2026
Latest reporting daySep 28, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-347Improper Verification of Cryptographic Signature
T1550.001Use Alternate Authentication Material: Application Access Token

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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