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CVE-2026-87853VulnerabilityPublished 09/09/2026Updated 10/21/2026

CVE-2026-87853: Partial String Comparison in Red Hat Red Hat Enterprise Linux 10

Affects Red Hat Red Hat Enterprise Linux 10Source CVE Database V5

0

Not known to be exploited · CVSS 7.5 High : monitor for a fix to Red Hat Red Hat Enterprise Linux 10.

Data as of 10/24/2026, 20:40:32 UTC

CVSS 3.1 base score
7.5High
How severe the flaw is on the 0–10 CVSS scale.
Exploitation

Not in CISA KEV, no exploitation reported

EPSS
0.3% chance of exploitation in 30 days – higher than 24% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

What to do

Affected software

ProductAffectedFixed in
Red HatRed Hat Enterprise Linux 10Affected–Fixed in–
Red HatRed Hat Enterprise Linux 6Affected–Fixed in–
Red HatRed Hat Enterprise Linux 7Affected–Fixed in–
Red HatRed Hat Enterprise Linux 8Affected–Fixed in–
Red HatRed Hat Enterprise Linux 9Affected–Fixed in–
Red HatRed Hat OpenShift Container Platform 4Affected–Fixed in–

AI-suggested

Red Hat has released an official security update for SSSD that fixes this vulnerability. Users of Red Hat Enterprise Linux 10 should apply the update as described in Red Hat advisory RHSA-2026:77534 and the referenced article https://access.redhat.com/articles/11258. Applying this update mitigates the vulnerability.

Description

CVE-2026-87853 is a vulnerability in the System Security Services Daemon (SSSD) of Red Hat Enterprise Linux 10. The flaw occurs in the IdP authentication provider where a partial string comparison is performed using strncmp(), allowing an attacker whose IdP identifier is a strict prefix of a target user's identifier to impersonate that user. This issue has a CVSS score of 7.5 and is rated as high severity. Red Hat has released an update to fix this vulnerability in SSSD.

Impact

An attacker can impersonate another user if their IdP identifier is a strict prefix of the target user's identifier, potentially gaining unauthorized access and privileges. This leads to confidentiality, integrity, and availability impacts as indicated by the CVSS vector (C:H/I:H/A:H).

Summary

The vulnerability exists in the eval_access_token_buf() function of SSSD's IdP authentication provider in Red Hat Enterprise Linux 10. The function compares the OIDC subject identifier using strncmp() with the length of the authenticated user's identifier, resulting in a prefix comparison rather than an exact match. This allows an attacker with an IdP identifier that is a strict prefix of another user's identifier to authenticate as that user, leading to cross-user impersonation. Red Hat has issued a security advisory and released patches addressing this issue.

References

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