Cyber Resilience

CVE-2026-87853

Published
09 September 2026
Modified
10 September 2026
CVSS Score v3.1 7.5
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
EPSS Score 0.0028 20th percentile
Risk Priority 54 floored blend · peak EPSS

CVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.

Summary

CVE-2026-87853 is a high-severity Partial String Comparison (CWE-187) vulnerability. Its CVSS base score is 7.5 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked at the 20th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

EU & UK References

Vulnerability Data

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…

more

a strict prefix of a target user's identifier can authenticate as the target user.

CWE(s)
CWE-187

Related Threats

MITRE ATT&CK Enterprise Techniques

T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1212 Exploitation for Credential Access Credential Access
Adversaries may exploit software vulnerabilities in an attempt to collect credentials.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

Affected Assets

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V10.4.1

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

ID.RA-01 partial match
prevents

Vulnerability identification processes can discover partial-comparison flaws during code or binary analysis.

PR.PS-06 partial match
prevents

Secure SDLC practices directly prevent unsafe string comparisons by enforcing proper API usage and testing.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.25 Secure development life cycle partial match
prevents

Secure development lifecycle practices can include requirements to avoid partial string comparisons in authentication or validation logic.

A.8.26 Application security requirements partial match
prevents

Application security requirements can mandate full, exact comparisons for sensitive operations.

A.8.27 Secure system architecture and engineering principles partial match
degrades

Secure system architecture principles discourage unsafe partial comparisons in critical paths.

A.8.28 Secure coding partial match
prevents

Secure coding standards can explicitly prohibit substring-based comparisons for security decisions.

A.8.29 Security testing in development and acceptance partial match
finds

Security testing can detect and prevent partial string comparison flaws before deployment.

A.8.5 Secure authentication partial match
degrades

Secure authentication mechanisms can reduce reliance on partial string comparisons for credential or token validation.

References