CVE-2026-87853 (GCVE-0-2026-87853)

Vulnerability from cvelistv5 – Published: 2026-09-09 16:06 – Updated: 2026-11-11 12:58
VLAI
Title
Sssd: sssd: idp authentication prefix comparison allows cross-user impersonation
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.
Severity
7.5 (High)
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
SSVC
Exploitation: none Automatable: no Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-09 18:28 UTC
CWE
  • CWE-187 - Partial String Comparison
Assigner
redhat CNA under the redhat root
CNA scorecard B 82/100 over 1204 records in the last 180 days details
References
URL Tags
https://access.redhat.com/errata/RHSA-2026:77534 vendor-advisoryx_refsource_REDHAT
https://access.redhat.com/errata/RHSA-2026:98559 vendor-advisoryx_refsource_REDHAT
https://access.redhat.com/security/cve/CVE-2026-87853 vdb-entryx_refsource_REDHAT
https://bugzilla.redhat.com/show_bug.cgi?id=2530888 issue-trackingx_refsource_REDHAT
Impacted products
Vendor Product Version CPE status
Red Hat Red Hat Enterprise Linux 10 Unaffected: 0:2.12.0-3.el10_2.2 , < * (rpm)
    cpe:/o:redhat:enterprise_linux:10.2
Create a notification for this product.
Red Hat Red Hat Enterprise Linux 10 Unaffected: 0:2.13.1-3.el10_3 , < * (rpm)
    cpe:/o:redhat:enterprise_linux:10.3
Create a notification for this product.
Red Hat Red Hat Enterprise Linux 6     cpe:/o:redhat:rhel_els:6
Create a notification for this product.
Red Hat Red Hat Enterprise Linux 7     cpe:/o:redhat:rhel_els:7
Create a notification for this product.
Red Hat Red Hat Enterprise Linux 8     cpe:/a:redhat:enterprise_linux:8
Create a notification for this product.
Red Hat Red Hat Enterprise Linux 9     cpe:/a:redhat:enterprise_linux:9
Create a notification for this product.
Red Hat Red Hat OpenShift Container Platform 4     cpe:/a:redhat:openshift:4
Create a notification for this product.
Red Hat Red Hat OpenShift Container Platform 5     cpe:/a:redhat:openshift:5
Create a notification for this product.
Date Public
2026-09-09 14:15
Credits
Red Hat would like to thank Moritz Theile for reporting this issue.
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              "value": "A flaw was found in SSSD\u0027s IdP authentication provider. The eval_access_token_buf() function compares the OIDC subject identifier using strncmp() with the authenticated user\u0027s identifier length, performing a prefix comparison instead of an exact match. An attacker whose IdP identifier is a strict prefix of a target user\u0027s identifier can authenticate as the target user."
            }
          ],
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                "type": "Red Hat severity rating"
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                "attackVector": "NETWORK",
                "availabilityImpact": "HIGH",
                "baseScore": 7.5,
                "baseSeverity": "HIGH",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "LOW",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H",
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              "descriptions": [
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                  "description": "Partial String Comparison",
                  "lang": "en",
                  "type": "CWE"
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              "name": "RHSA-2026:98559",
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              "name": "RHBZ#2530888",
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              "time": "2026-09-06T00:00:00.000Z",
              "value": "Reported to Red Hat."
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              "lang": "en",
              "time": "2026-09-09T14:15:45.513Z",
              "value": "Made public."
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          ],
          "title": "Sssd: sssd: idp authentication prefix comparison allows cross-user impersonation",
          "workarounds": [
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              "lang": "en",
              "value": "Deployments not using the IdP authentication provider (idp_type = keycloak) are not affected. For affected deployments: (1) If using Keycloak LDAP federation, switching to Import Users: enabled mode causes Keycloak to assign random UUIDs as sub claims, making prefix collisions astronomically unlikely. (2) Restrict PAM login to specific users via simple_allow_users or access_provider = simple. (3) Disable Keycloak self-registration to prevent attackers from creating accounts with chosen prefix usernames."
            }
          ],
          "x_generator": {
            "engine": "cvelib 1.8.0"
          },
          "x_redhatCweChain": "CWE-187: Partial String Comparison"
        }
      },
      "cveMetadata": {
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        "assignerShortName": "redhat",
        "cveId": "CVE-2026-87853",
        "datePublished": "2026-09-09T16:06:25.638Z",
        "dateReserved": "2026-09-09T13:00:35.698Z",
        "dateUpdated": "2026-11-11T12:58:51.396Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
Vulnerability timeline

Sightings and recorded dates, grouped by day · UTC

JSON
How durations are calculated

Following the VTEM framework (Black Hat USA 2015), time to patch starts when the vendor or a coordinator was informed, total time to patch at discovery, and disclosure to patch at public disclosure; vendor response time runs from the report to its acknowledgement. Time to exploit and time unpatched start at the earliest discovery or report, falling back to public disclosure. Unpatched time ends at the first recorded patch, or the calculation time when no patch is recorded. Exploitation to patch shows the interval between those two events; a published proof of concept is a public exploit, not exploitation.

Each result shows its source dates. A negative interval means the end event came first; when date-only inputs leave the order open, the result says so. Date-only inputs are approximate. The earliest evidence wins: KEV report dates and sightings are labelled as such. Records describing another vulnerability are listed but never calculated from, and a PoC alone does not establish exploitation. Missing patch evidence does not prove that no patch exists. Filters below change the event list only.

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    Related by attack behaviour

    Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.