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Red Hat Keycloak CVE-2026-18967

| EUVDEUVD-2026-53716 HIGH
Authentication Bypass by Capture-replay (CWE-294)
2026-08-06 redhat GHSA-fghp-hcwh-75j2
8.1
CVSS 3.1 · NVD
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Severity by source

Vendor (redhat) PRIMARY
MEDIUM
qualitative
NVD
8.1 HIGH
AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
vuln.today AI
8.1 HIGH

AV:A because assertion capture requires network adjacency; PR:N and UI:N once the assertion is obtained; no availability impact from session hijacking.

3.1 AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
4.0 AV:A/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
Red Hat
6.4 MEDIUM
qualitative

Primary rating from Vendor (redhat).

CVSS VectorNVD

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Attack Vector
Adjacent
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

Lifecycle Timeline

5
Analysis Updated
Aug 10, 2026 - 19:30 vuln.today
v2 (cvss_changed)
Re-analysis Queued
Aug 10, 2026 - 19:22 vuln.today
cvss_changed
Severity Changed
Aug 10, 2026 - 19:22 NVD
MEDIUM HIGH
CVSS changed
Aug 10, 2026 - 19:22 NVD
6.4 (MEDIUM) 8.1 (HIGH)
Analysis Generated
Aug 06, 2026 - 07:01 vuln.today

DescriptionNVD

A flaw was found in the SAML broker component of Keycloak, an identity and access management solution. When configured as a SAML broker using the IdP-Initiated flow, Keycloak fails to enforce the OneTimeUse condition in SAML assertions. This allows an attacker who captures a valid, unused assertion to replay it multiple times. Successful exploitation could allow an attacker to hijack a user's session and gain unauthorized access to the system as that user.

AnalysisAI

Session hijacking via SAML assertion replay in Keycloak's SAML broker component allows adjacent-network attackers to authenticate as arbitrary users without credentials. When Keycloak is deployed as a SAML broker in IdP-Initiated flow mode, it fails to enforce the SAML OneTimeUse condition, permitting a captured assertion to be submitted multiple times. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Gain network-adjacent position
Delivery
Wait for victim IdP-Initiated login
Exploit
Intercept SAML assertion in transit
Execution
Replay assertion to Keycloak SAML broker endpoint
Persist
Keycloak issues authenticated session
Impact
Access applications as victim user

Vulnerability AssessmentAI

Exploitation Exploitation requires that Keycloak is explicitly configured as a SAML broker using the IdP-Initiated SSO flow - this is a non-default deployment mode that must be deliberately enabled. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The CVSS 8.1 score is credible but requires careful unpacking. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker positioned on the same network segment as an enterprise's Keycloak deployment - for example, via a compromised internal host or a rogue device on a corporate VLAN - intercepts a SAML assertion issued by the corporate IdP to a legitimate user during an IdP-Initiated login. The attacker replays that same assertion to Keycloak's SAML broker endpoint before it expires, and because Keycloak does not track or reject reused assertions, it issues a full authenticated session token, granting the attacker access to all applications protected by Keycloak as the victim user. …
Remediation Apply the patch released by Red Hat per the vendor advisory at https://access.redhat.com/security/cve/CVE-2026-18967; a specific patched version number is not independently confirmed from the available data, so consult the advisory directly for the exact target release. … Detailed patch versions, workarounds, and compensating controls in full report.

Recommended ActionAI

Within 24 hours, identify all Keycloak instances configured as SAML brokers operating in IdP-Initiated flow mode and document their dependent applications. …

Sign in for detailed remediation steps and compensating controls.

Threat intelligence, references, and detailed analysis are available after sign-in.

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Vendor StatusVendor

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CVE-2026-18967 vulnerability details – vuln.today

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