Red Hat Build of Keycloak: Authentication Bypass by Capture-replay
CVE-2026-18967 is a high-severity authentication bypass by capture-replay vulnerability in Red Hat Build of Keycloak from Red Hat, with a CVSS 3.1 base score of 8.1 out of 10. It can be exploited from the same local network by an unauthenticated attacker, without any action from a user. There is no confirmed exploitation so far. EPSS estimates a 0.23% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Check which version of Red Hat Build of Keycloak you run against the affected versions below, and install the vendor's latest release.
- Read the advisory on access.redhat.com for workarounds and exact fixed builds.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Red Hat | Red Hat Build of Keycloak | Not specified in the record | Not stated |
| Red Hat | Red Hat JBoss Enterprise Application Platform Expansion Pack | Not specified in the record | Not stated |
| Red Hat | Red Hat Single Sign-On 7 | Not specified in the record | Not stated |
| Red Hat | Build Of Keycloak | Not specified in the record | Not stated |
| Red Hat | Jboss Enterprise Application Platform Expansion Pack | Not specified in the record | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- AdjacentThe attacker must be on the same local network segment.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- NoneAvailability is not affected.
Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 6.4 | Medium | CNA (redhat.com) |
| CVSS 3.1 | 8.1 | High | NVD |
Official description
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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Authentication Bypass by Capture-replay
A capture-replay flaw exists when the design of the product makes it possible for a malicious user to sniff network traffic and bypass authentication by replaying it to the server in question to the same effect as the original message (or with minor changes).
How developers prevent this class of flaw
- Utilize some sequence or time stamping functionality along with a checksum which takes this into account in order to ensure that messages can be parsed only once.
- Since any attacker who can listen to traffic can see sequence numbers, it is necessary to sign messages with some kind of cryptography to ensure that sequence numbers are not simply doctored along with content.
More Authentication Bypass by Capture-replay vulnerabilities (CWE-294)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Other references
- bugzilla.redhat.com/show_bug.cgi?id=2511604Permissions Required
Other vulnerabilities in Red Hat Build of Keycloak
- 9.1 Critical severity
- 7.7 High severity
- 7.5 High severity
- 7.5 High severity
- 7.4 High severity
- 7.4 High severity
Recent Authentication Bypass by Capture-replay vulnerabilities
- 9.8 Critical severity
- 9.1 Critical severity
- 9.8 Critical severity
- 8.2 High severity
- 7.4 High severity
- 9.8 Critical severity
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