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Fencer Vulns
medium 4.2

CVE-2026-18211 json

Keycloak-services: keycloak-services: secure-client-uris policy bypass via localhost-prefixed domains

published 2026-07-31 3 mo ago modified 2026-08-31 2 mo ago also EUVD-2026-51483

cvss
4.2
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 23%
public exploits
0
none known

Summary

A flaw was found in the secure-client-uris client policy executor within Keycloak core services. This component is responsible for enforcing security requirements on client configurations, such as requiring encrypted connections for redirect URIs. Due to an improper check that only looks at the start of a web address rather than properly verifying the host, an attacker can bypass these security restrictions by using a specially crafted domain name. This could allow an attacker to intercept sensitive authentication codes over unencrypted connections.

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-2026-18211 updated cvss 4.2

keycloak-services: keycloak-services: secure-client-uris policy bypass via localhost-prefixed domains

  • Red Hat Build of Keycloak rhbk-keycloak-rhel9, rhbk-openshift-rhel9, keycloak-services 26.6.4.redhat-00004
    affected: workaround, no fix available
  • Red Hat Data Grid 8 keycloak-services 26.6.4.redhat-00004 Red Hat JBoss Enterprise Application Platform Expansion Pack keycloak-services 26.6.4.redhat-00004 Red Hat Single Sign-On 7 keycloak-services 26.6.4.redhat-00004
    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

0.31% chance of exploitation in the next 30 days, higher than 23% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 4.2 CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:N
NVD 3.1 5.4 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N

Affected products

  • 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-20 Improper Input Validation

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.