https://seclists.org/oss-sec/2026/q4/16: CVE-2026-56154: Apache HTTP Server: mod_write use-after-fe via %{LA-U:HTTP:...}

Q: Which Apache HTTP Server versions need remediation?

Apache HTTP Server versions 2.4.0 through 2.4.68 are affected. The issue was fixed in the 2.4.x branch by revision r1938660, and version 2.4.69 was released on 2026-10-01.

Q: What configuration condition is required for exploitation?

The vulnerability is in mod_rewrite when lookahead expressions using %{LA-U:HTTP:...} are used. The provided information does not establish that installations without this mod_rewrite usage are affected.

Q: What should be done if an immediate upgrade is not possible?

Review mod_rewrite rules for use of %{LA-U:HTTP:...} lookahead expressions and avoid or remove that usage until the server can be updated to a fixed 2.4.x release.

Published Oct 1, 2026

Updated

Affected Software

1 affected component

Apache HTTP Server>=2.4.0<=2.4.68

Frequently Asked Questions

Which Apache HTTP Server versions need remediation?

Apache HTTP Server versions 2.4.0 through 2.4.68 are affected. The issue was fixed in the 2.4.x branch by revision r1938660, and version 2.4.69 was released on 2026-10-01.

What configuration condition is required for exploitation?

The vulnerability is in mod_rewrite when lookahead expressions using %{LA-U:HTTP:...} are used. The provided information does not establish that installations without this mod_rewrite usage are affected.

What should be done if an immediate upgrade is not possible?

Review mod_rewrite rules for use of %{LA-U:HTTP:...} lookahead expressions and avoid or remove that usage until the server can be updated to a fixed 2.4.x release.