CVE-2026-9689
Description
A flaw was found in Keycloak, an open-source identity and access management solution. When a client application is configured to accept broad redirect Uniform Resource Identifiers (URIs), a remote attacker can manipulate the authentication process by crafting a special web address. If a user clicks this link, the client application might incorrectly prioritize attacker-controlled information over legitimate data. This vulnerability, known as HTTP parameter pollution, could allow an attacker to bypass security measures or gain unauthorized access to resources.
AI Insight
LLM-synthesized narrative grounded in this CVE's description and references.
Keycloak OIDC redirect URI handling suffers from HTTP parameter pollution, allowing attackers to bypass security measures if clients use wildcard URIs and first-wins parsing.
Vulnerability
A flaw exists in Keycloak's OIDC redirect URI handling when a client application is configured with a wildcard redirect URI (e.g., http://localhost:8080/*). The OIDCRedirectUriBuilder.addParam() method appends Keycloak's own response parameters (iss, code, state, session_state) without checking for duplicates, leading to a polluted redirect URL with duplicate parameters. This vulnerability, known as HTTP parameter pollution, affects all versions of Keycloak [1][2].
Exploitation
An attacker can craft a malicious authorization URL that includes attacker-controlled values for the OIDC response parameters within the redirect URI. The victim must click this crafted link and successfully authenticate. Additionally, the client application must use a first-wins parsing strategy for duplicate query parameters [2].
Impact
If the client application uses first-wins parsing, it may incorrectly prioritize the attacker-supplied parameter values over the legitimate ones generated by Keycloak. This could allow the attacker to bypass security measures or gain unauthorized access to resources [1][2].
Mitigation
No fix is disclosed in the available references. As a workaround, administrators should avoid using wildcard redirect URIs in client configurations. If wildcard URIs are necessary, ensure the client application uses a last-wins parsing strategy for duplicate parameters [2].
AI Insight generated on May 27, 2026. Synthesized from this CVE's description and the cited reference URLs; citations are validated against the source bundle.
Affected products
2Patches
0No patches discovered yet.
Vulnerability mechanics
No source-code context for this CVE — mechanics is only generated when we can read the actual fix diff. Without that, the four sections (root cause, attack vector, affected code, fix) would be speculation rather than analysis.
References
2News mentions
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