Severity by source
AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
AV:A because assertion capture requires network adjacency; PR:N and UI:N once the assertion is obtained; no availability impact from session hijacking.
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
Lifecycle Timeline
5DescriptionNVD
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
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. …
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Same weakness CWE-294 – Authentication Bypass by Capture-replay
View allSame technique Authentication Bypass
View allVendor StatusVendor
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External POC / Exploit Code
Leaving vuln.today
EUVD-2026-53716
GHSA-fghp-hcwh-75j2