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Fencer Vulns
low 3.4

CVE-2026-18209 json

Keycloak-services: keycloak-services: oidc redirect_uri fragment bypass in http parameter pollution check

published 2026-07-31 3 mo ago modified 2026-09-17 52 d ago also BIT-keycloak-2026-18209 , EUVD-2026-51487

cvss
3.4
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 35%
public exploits
0
none known

Summary

A flaw was found in the keycloak-services component of Keycloak, which handles OpenID Connect (OIDC) authentication flows. The issue occurs because the security check designed to prevent HTTP parameter pollution only inspects the query portion of a redirect URL and ignores the fragment portion. When a client is configured with a wildcard redirect URI, an attacker can use this to inject duplicate security parameters into the login response. If a client application is not configured correctly, it might trust the attacker's injected data instead of the real security information from Keycloak, leading to session fixation or account confusion.

Patch / fix

  • bitnami keycloak 26.7.3
  • Red Hat Red Hat build of Keycloak 26.6 26.6-20, 26.6.7-3

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-2026-18209 updated cvss 3.4

keycloak-services: keycloak-services: OIDC redirect_uri fragment bypass in HTTP parameter pollution check

  • Red Hat build of Keycloak 26.6 rhbk/keycloak-rhel9 26.6-20, rhbk/keycloak-rhel9-operator 26.6-20, rhbk/keycloak-operator-bundle 26.6.7-3
    fixed: vendor fix RHSA-2026:68277
  • Red Hat build of Keycloak 26.6.7
    fixed: vendor fix RHSA-2026:68278
  • Red Hat Data Grid 8 keycloak-services 23.0.7 Red Hat JBoss Enterprise Application Platform Expansion Pack keycloak-services 23.0.7 Red Hat Single Sign-On 7 keycloak-services 23.0.7
    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
partial
Assessed
3 mo ago

Exploit prediction

0.41% chance of exploitation in the next 30 days, higher than 35% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 3.4 CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:N/I:L/A:N
NVD 3.1 4.7 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N
OSV 3.1 4.7 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:L/A:N

Affected packages

ecosystem package affected fixed in
bitnami keycloak
<26.7.3
26.7.3

Affected products

  • Red Hat Red Hat build of Keycloak 26.6
  • Red Hat Red Hat build of Keycloak 26.6.7
  • 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-1288 Improper Validation of Consistency within Input

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.