CyberSecBulletin
CVE-2026-91184NVD status: Awaiting Analysis

NGINX Gateway Fabric: Improper Neutralization of Equivalent Special Elements

Published Updated By the CyberSecBulletin desk

CVE-2026-91184 is a high-severity improper neutralization of equivalent special elements vulnerability in NGINX Gateway Fabric from F5, with a CVSS 3.1 base score of 8.8 out of 10. It can be exploited remotely over the network by an attacker with a low-privileged account, without any action from a user. The record lists version 2.8.0 as the first without the flaw, so updating NGINX Gateway Fabric to that release or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.48% chance of exploitation within 30 days, which is low compared with other CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update NGINX Gateway Fabric to 2.8.0 or a later version.

Affected products and versions

VendorProductAffected versionsFixed in
F5NGINX Gateway Fabric2.4.0 up to, but not including, 2.8.02.8.0

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
NetworkCan be exploited remotely over a network, including the internet.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
LowA basic user account is enough.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by CNA (f5.com).

Scoring systemScoreSeverityScored by
CVSS 4.08.7HighCNA (f5.com)
CVSS 3.18.8HighCNA (f5.com)

Official description

Description NGINX Gateway Fabric has a vulnerability when it renders the spec.basic.realm (and spec.jwt.realm) field of a namespaced AuthenticationFilter verbatim, unescaped and unvalidated, into the shared data-plane nginx.conf as auth_basic "<realm>";. A namespaced authenticated attacker that configures AuthenticationFilter CRD to an HTTPRoute/GRPCRoute on a shared Gateway can craft a realm value that closes the quoted directive and the enclosing location {} block and injects arbitrary NGINX directives into that Gateway's data-plane config. Impact A remote authenticated attacker can send crafted requests to configure NGINX Gateway Fabric AuthenticationFilter CRD and may be able to read every co-located tenant's mounted secrets, SSRF via proxy_pass, reading the pod ServiceAccount token, or hijacking other tenants' routes. There is no data plane exposure; this is a control plane issue only. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Improper Neutralization of Equivalent Special Elements

The product correctly neutralizes certain special elements, but it improperly neutralizes equivalent special elements.

How developers prevent this class of flaw

  • Programming languages and supporting technologies might be chosen which are not subject to these issues.
  • Utilize an appropriate mix of allowlist and denylist parsing to filter equivalent special element syntax from all input.

More Improper Neutralization of Equivalent Special Elements vulnerabilities (CWE-76)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
  3. Record last changed materially (score, affected products, status or references).

References

Other vulnerabilities in NGINX Gateway Fabric

All NGINX Gateway Fabric vulnerabilities

Recent Improper Neutralization of Equivalent Special Elements vulnerabilities

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