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Mitigating Apache HTTP/2 CVE-2026-23918 by Disabling mod_http2 Before a Distro Patch Ships

🛑 Problem

CVE-2026-23918 is a double-free vulnerability (possible RCE) in Apache's HTTP/2 handler (mod_http2). A patched Apache (2.4.67+) fixes it, but distro package repos can lag the upstream fix by days or weeks — Fedora had not yet shipped 2.4.67 when this was applied against a server running 2.4.66. Waiting for the distro patch means running a known-RCE-capable code path in the meantime.

🩹 Mitigation — Disable HTTP/2 Entirely

If nothing on the site specifically depends on HTTP/2 (no HTTP/2-only feature, no client that refuses to negotiate HTTP/1.1), the fastest safe mitigation is unloading mod_http2 outright rather than waiting for a package update.

1. Comment out the module-loading directives. These typically live in Fedora/RHEL-family layouts at:

/etc/httpd/conf.modules.d/10-h2.conf
/etc/httpd/conf.modules.d/10-proxy_h2.conf

Comment out the LoadModule line(s) in each — back up the originals first (a plain .bak copy alongside each file is enough; this is a two-line change, not worth a full config snapshot).

2. Reload, don't just check syntax:

apachectl configtest   # confirm no syntax errors from the comment-out
systemctl reload httpd

3. Verify the module actually unloaded:

httpd -M | grep -i http2   # expect: no output

4. Check for user-visible regressions. Any HTTP/2-dependent client falls back to HTTP/1.1 automatically per the protocol negotiation spec — for a typical webmail/app frontend (SnappyMail, Roundcube, a WordPress site, etc.) there should be no visible difference. Confirm by loading the site and checking the protocol Chrome/Firefox devtools report for the connection (should now show http/1.1).

🔁 Rollback (once the distro ships the fix)

dnf update httpd     # or apt, depending on distro — confirm version ≥ the patched release
# restore the commented-out LoadModule lines from the .bak files
apachectl configtest
systemctl reload httpd
httpd -M | grep -i http2   # now expect: http2_module present

Don't restore the modules purely because a patched package is available — confirm the installed version actually reports the fixed version string (httpd -v) before re-enabling the vulnerable code path's replacement.

🧭 When this mitigation isn't viable

If the site genuinely needs HTTP/2 (server push in active use, a client that hard-requires it, or a measurable latency regression from the fallback to HTTP/1.1 under real load), disabling the module isn't an option and the real fix is forcing the distro update sooner (backport from a newer Fedora/EPEL release, or building httpd from a patched source RPM) rather than waiting on the normal update cadence.

  • 30-Areas/MajorInfrastructure/Servers/majormail.md § Incident Log — the specific deployment this was applied to