OIDC session fixation via unchecked redirect fragments
Published Jul 31, 2026 · Updated Jul 31, 2026
HTTP parameter pollution in Red Hat build of Keycloak allows remote attackers to inject duplicate OIDC response parameters. RedirectUtils checks the query portion of wildcard redirect URIs for forbidden security parameters but fails to inspect the URI fragment. Exploitation requires user interaction, a wildcard redirect URI, and a non-conformant relying party that trusts injected data, enabling session fixation or account confusion.
Summary
What happened
HTTP parameter pollution in Red Hat build of Keycloak allows remote attackers to inject duplicate OIDC response parameters. RedirectUtils checks the query portion of wildcard redirect URIs for forbidden security parameters but fails to inspect the URI fragment. Exploitation requires user interaction, a wildcard redirect URI, and a non-conformant relying party that trusts injected data, enabling session fixation or account confusion.
The record
- CVE
- CVE-2026-18209
- Published
- Jul 31, 2026
- Updated
- Jul 31, 2026
- Vendor
- 389 Directory Server
- Product
- Red Hat build of Keycloak
- Classifications
- CWE-1288
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jul 31, 2026CVE publishedPublication date reported by the CVE source.
- Jul 31, 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?
Affected versions are unavailable in this record. Check the vendor advisory for version and patch details.
What conditions does exploitation require?
What is affected?
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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