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CVE-2026-29167 – Use After Free in mod_ldap – Apache HTTP Server 2.4.0 through 2.4.67

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Summary

CVE-2026-29167 is a Use After Free vulnerability (CWE-416) in the mod_ldap module of Apache HTTP Server, triggered when mod_ldap is configured in per-directory mode. It affects all Apache HTTP Server releases from 2.4.0 through 2.4.67 and carries a CVSS v3.1 base score of 9.8 (Critical), reflecting full compromise of confidentiality, integrity, and availability exploitable by unauthenticated remote attackers. A fix is available in Apache HTTP Server 2.4.68, released June 8, 2026.

Technical details

  • Root cause: A use-after-free memory safety flaw (CWE-416) in the mod_ldap module — memory that has been freed is subsequently accessed, leading to memory corruption.
  • Trigger condition: The vulnerability is present when mod_ldap is configured at the per-directory level, for example via <Directory> blocks or .htaccess files enabling LDAP-based authentication on specific paths.
  • Attack vector: Network-accessible with no authentication and no user interaction required (AV:N/AC:L/PR:N/UI:N), allowing unauthenticated remote attackers to trigger the flaw over standard HTTP/HTTPS.
  • Impact: Full compromise of confidentiality, integrity, and availability (C:H/I:H/A:H), consistent with the severe outcomes of exploitable use-after-free memory corruption.

Affected software

  • Apache HTTP Server 2.4.0 through 2.4.67 (inclusive), when mod_ldap is configured in per-directory mode.

Severity

CVSS v3.1 base score: 9.8 (Critical)
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate action: Upgrade to Apache HTTP Server 2.4.68, released June 8, 2026, which resolves this vulnerability (fix committed as revision r1934935 on June 3, 2026).
  • If immediate patching is not feasible: Disable the mod_ldap module or remove per-directory LDAP configuration directives until the upgrade can be applied to eliminate the vulnerable code path.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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