CVE-2026-87853 vulnerability in Red Hat Products
Published on September 9, 2026
Sssd: sssd: idp authentication prefix comparison allows cross-user impersonation
A flaw was found in SSSD's IdP authentication provider. The eval_access_token_buf() function compares the OIDC subject identifier using strncmp() with the authenticated user's identifier length, performing a prefix comparison instead of an exact match. An attacker whose IdP identifier is a strict prefix of a target user's identifier can authenticate as the target user.
Vulnerability Analysis
CVE-2026-87853 can be exploited with network access, and requires small amount of user privileges. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to be very high.
Timeline
Reported to Red Hat.
Made public. 3 days later.
Weakness Type
Partial String Comparison
The software performs a comparison that only examines a portion of a factor before determining whether there is a match, such as a substring, leading to resultant weaknesses. For example, an attacker might succeed in authentication by providing a small password that matches the associated portion of the larger, correct password.
Products Associated with CVE-2026-87853
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