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CVE-2026-57941 – Use-After-Free / Potential RCE – Apache HTTP Server 2.4.0–2.4.68

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Summary

CVE-2026-57941 is a use-after-free vulnerability (CWE-416) in Apache HTTP Server’s mod_http2 module, caused by re-entrancy issues around a shared session->bbtmp buffer. It affects Apache HTTP Server versions 2.4.0 through 2.4.68 and carries a CVSS v3.1 base score of 9.8 (Critical), reflecting a network-exploitable, low-complexity attack path with no authentication or user interaction required.

Technical details

  • Root cause: Re-entrant handling of a shared temporary bucket brigade (session->bbtmp) within mod_http2 leads to memory being freed and subsequently reused/accessed (use-after-free).
  • Trigger conditions: Exploitation requires the mod_http2 module to be enabled and HTTP/2 connections processed by the affected server.
  • Attack vector: Remote, network-based; no privileges or user interaction required (AV:N/AC:L/PR:N/UI:N).
  • Impact: The CVSS vector indicates high impact to confidentiality, integrity, and availability, consistent with memory-corruption issues that can lead to crashes (denial of service) or, depending on exploitability, more severe outcomes such as remote code execution.

Affected software

  • Apache HTTP Server versions 2.4.0 through 2.4.68 (inclusive), when mod_http2 is enabled.

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: Upgrade Apache HTTP Server to version 2.4.69 or later, which contains the fix for this issue (committed upstream as revision r1938665).
  • If no patch can be applied immediately: Disable the mod_http2 module (or disable HTTP/2 protocol negotiation) on affected servers until the upgrade can be performed, since the flaw is specific to HTTP/2 request handling.

References

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