CVE-2026-15571: Keycloak-services: keycloak-services: predictable account-linking hash enables account takeover via malicious oidc client

Severity: high (CVSS 7.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-08-18 · updated 2026-08-20
Weakness: CWE-341

Description

A flaw was found in the legacy client-initiated account-linking endpoint of Keycloak, a widely used open-source identity and access management solution. The mechanism used to protect the account-linking process from unauthorized requests relies on a hash that can be predicted by a malicious OIDC client. By tricking a user into authenticating, an attacker-controlled client can forge a valid linking URL to connect the victim's account to an attacker's external identity. This results in a full account takeover, allowing the attacker to log in as the victim.

Affected products

Red Hat build of Keycloak 26.4: all versions — fixed in 26.6-12, 26.6.6-1

How to fix

Upgrade to a fixed version: Red Hat build of Keycloak 26.4 26.6-12, 26.6.6-1. Check the vendor advisory for mitigations.

References

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