Unauthorized access via duplicate OIDC response parameters
Published May 27, 2026 · Updated May 27, 2026
HTTP parameter pollution in Red Hat build of Keycloak allows remote attackers to gain unauthorized access via a crafted authorization URL. OIDCRedirectUriBuilder.addParam() appends generated iss, code, state, and session_state values without rejecting identical parameters already present in a wildcard-matched redirect URI. Exploitation requires a wildcard redirect URI, a user click and completed authentication, and a client parser that accepts the attacker-controlled first duplicate.
Summary
What happened
HTTP parameter pollution in Red Hat build of Keycloak allows remote attackers to gain unauthorized access via a crafted authorization URL. OIDCRedirectUriBuilder.addParam() appends generated iss, code, state, and session_state values without rejecting identical parameters already present in a wildcard-matched redirect URI. Exploitation requires a wildcard redirect URI, a user click and completed authentication, and a client parser that accepts the attacker-controlled first duplicate.
The record
- CVE
- CVE-2026-9689
- Published
- May 27, 2026
- Updated
- May 27, 2026
- Vendor
- 389 Directory Server
- Product
- Red Hat build of Keycloak
- Classifications
- CWE-1288, T1566.002
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- May 27, 2026CVE publishedPublication date reported by the CVE source.
- May 27, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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