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Fencer Vulns
high 8.1

CVE-2026-11800 json

Org.keycloak:keycloak-services: keycloak: authentication bypass via jwt algorithm confusion

published 2026-06-25 4 mo ago modified 2026-11-03 5 d ago also BIT-keycloak-2026-11800 , EUVD-2026-39567 , GHSA-j97h-3f8r-mrjr

cvss
8.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 22%
public exploits
0
none known

Summary

A flaw was found in Keycloak. This JWT algorithm confusion vulnerability in the JWT Authorization Grant flow allows an attacker with valid client credentials to bypass signature verification. By forging an assertion, the attacker can create unauthorized access tokens. This enables the attacker to impersonate any federated user linked to the affected Identity Provider, leading to unauthorized access and potential privilege escalation.

Patch / fix

  • maven org.keycloak:keycloak-services 26.6.4
  • bitnami keycloak 26.6.4
  • Red Hat Red Hat build of Keycloak 26.6 26.6-8, 26.6.4-2

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-11800 updated cvss 8.1

org.keycloak:keycloak-services: Keycloak: Authentication bypass via JWT algorithm confusion

  • Red Hat Build of Keycloak rhbk/keycloak-rhel9
    affected: no fix available
  • Red Hat build of Keycloak 26.6 rhbk/keycloak-rhel9 26.6-8, rhbk/keycloak-rhel9-operator 26.6-8, rhbk/keycloak-operator-bundle 26.6.4-2
    fixed: vendor fix RHSA-2026:30084
  • Red Hat build of Keycloak 26.6.4
    fixed: vendor fix RHSA-2026:30083
  • Red Hat Build of Keycloak rhbk-openshift-rhel9 Red Hat Data Grid 8 keycloak-services Red Hat JBoss Enterprise Application Platform Expansion Pack keycloak-services Red Hat Single Sign-On 7 keycloak-services
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
total
Assessed
4 mo ago

Exploit prediction

0.30% chance of exploitation in the next 30 days, higher than 22% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 8.1 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
CISA ADP 3.1 8.1 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
GitHub 3.1 8.1 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
OSV 3.1 8.1 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

Affected packages

ecosystem package affected fixed in
maven org.keycloak:keycloak-services
<26.6.4
26.6.4
bitnami keycloak
>=26.6.0, <26.6.4
26.6.4

Affected products

  • Red Hat Red Hat build of Keycloak 26.6
  • Red Hat Red Hat build of Keycloak 26.6.4
  • Red Hat Red Hat Build of Keycloak
  • Red Hat Red Hat Data Grid 8
  • Red Hat Red Hat JBoss Enterprise Application Platform Expansion Pack
  • Red Hat Red Hat Single Sign-On 7

Classification

Weakness
  • CWE-347 Improper Verification of Cryptographic Signature

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.