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Fencer Intel
high 7.5

CVE-2026-87853 json

Sssd: sssd: idp authentication prefix comparison allows cross-user impersonation

published 2mo ago modified 16h ago also EUVD-2026-75084

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 26%
public exploits
0
none known

Summary

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.

Patch / fix

  • Red Hat Red Hat Enterprise Linux 10 0:2.12.0-3.el10_2.2, 0:2.13.1-3.el10_3
  • sssd RHEL 10.2 2.12.0-3.el10_2.2
  • sssd-ad RHEL 10.2 2.12.0-3.el10_2.2
  • sssd-idp RHEL 10.2 2.12.0-3.el10_2.2
  • sssd-ipa RHEL 10.2 2.12.0-3.el10_2.2
  • sssd-kcm RHEL 10.2 2.12.0-3.el10_2.2
  • sssd-dbus RHEL 10.2 2.12.0-3.el10_2.2
  • sssd-krb5 RHEL 10.2 2.12.0-3.el10_2.2
  • sssd-ldap RHEL 10.2 2.12.0-3.el10_2.2

red hat advisories RHSA-2026:77534

  • sssd openSUSE Tumbleweed 2.13.1-3.1

opensuse advisories openSUSE-SU-2026:11825-1

  • sssd AlmaLinux 10 2.12.0-3.el10_2.2
  • sssd-ad AlmaLinux 10 2.12.0-3.el10_2.2
  • sssd-idp AlmaLinux 10 2.12.0-3.el10_2.2
  • sssd-ipa AlmaLinux 10 2.12.0-3.el10_2.2
  • sssd-kcm AlmaLinux 10 2.12.0-3.el10_2.2
  • sssd-dbus AlmaLinux 10 2.12.0-3.el10_2.2
  • sssd-krb5 AlmaLinux 10 2.12.0-3.el10_2.2
  • sssd-ldap AlmaLinux 10 2.12.0-3.el10_2.2

almalinux advisories ALSA-2026:77534

  • sssd Rocky Linux 10 2.12.0-3.el10_2.2

rocky linux advisories RLSA-2026:77534

Is CVE-2026-87853 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-87853 updated cvss 7.5

sssd: sssd: IdP authentication prefix comparison allows cross-user impersonation

  • Red Hat Enterprise Linux 6 sssd, sssd-ad, sssd-ipa, sssd-dbus, sssd-krb5, sssd-ldap, +19 more
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux AppStream (v. 10) sssd-idp 2.13.1-3.el10_3, sssd-idp 2.12.0-3.el10_2.2 Red Hat Enterprise Linux BaseOS (v. 10) sssd 2.13.1-3.el10_3, sssd 2.12.0-3.el10_2.2, sssd-ad 2.13.1-3.el10_3, sssd-ipa 2.13.1-3.el10_3, sssd-kcm 2.13.1-3.el10_3, sssd-ad 2.12.0-3.el10_2.2, +48 more Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) sssd-debuginfo 2.13.1-3.el10_3, sssd-debuginfo 2.12.0-3.el10_2.2, sssd-debugsource 2.13.1-3.el10_3, sssd-ad-debuginfo 2.13.1-3.el10_3, sssd-debugsource 2.12.0-3.el10_2.2, sssd-idp-debuginfo 2.13.1-3.el10_3, +52 more
    fixed: vendor fix RHSA-2026:77534
  • Red Hat Enterprise Linux 7 sssd, sssd-ad, sssd-ipa, sssd-kcm, sssd-dbus, sssd-krb5, +24 more Red Hat Enterprise Linux 8 sssd, sssd-ad, sssd-idp, sssd-ipa, sssd-kcm, sssd-dbus, +24 more Red Hat Enterprise Linux 9 sssd, sssd-ad, sssd-idp, sssd-ipa, sssd-kcm, sssd-dbus, +24 more Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-8, openshift/ose-rhel-coreos-9 Red Hat OpenShift Container Platform 5 openshift/ose-rhel-coreos-9
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
total
Assessed
2mo ago

Exploit prediction

0.33% chance of exploitation in the next 30 days, higher than 26% of all scored CVEs (FIRST EPSS, 2026-11-11).

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

Affected products

  • Red Hat Red Hat Enterprise Linux 10
  • Red Hat Red Hat Enterprise Linux 6
  • Red Hat Red Hat Enterprise Linux 7
  • Red Hat Red Hat Enterprise Linux 8
  • Red Hat Red Hat Enterprise Linux 9
  • Red Hat Red Hat OpenShift Container Platform 4
  • Red Hat Red Hat OpenShift Container Platform 5

Classification

Weakness
  • CWE-187 Partial String Comparison

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.