Public bug reported:
After the ESM update to apache2 2.4.29-1ubuntu4.27+esm7 (built
2026-05-21), Apache fails to start whenever mod_http2 is enabled. The
dynamic loader rejects the module because of an undefined symbol that no
shipped binary or library actually exports.
This is a regression introduced by the +esm7 build itself, not a
configuration problem.
## Steps to reproduce
1. Ubuntu 18.04 (bionic) with ESM enabled.
2. apache2 with mod_http2 enabled (a2enmod http2).
3. Upgrade to apache2-bin 2.4.29-1ubuntu4.27+esm7.
4. Restart apache: sudo systemctl restart apache2.
## Expected result
Apache starts and serves HTTP/2.
## Actual result
apache2.service enters failed state:
apache2: Syntax error on line 146 of /etc/apache2/apache2.conf:
Syntax error on line 1 of /etc/apache2/mods-enabled/http2.load:
Cannot load /usr/lib/apache2/modules/mod_http2.so into server:
/usr/lib/apache2/modules/mod_http2.so: undefined symbol: H2_MPLX_MSG
## Diagnostic evidence
### 1. Both files belong to the same package/build
$ dpkg -S /usr/lib/apache2/modules/mod_http2.so
apache2-bin: /usr/lib/apache2/modules/mod_http2.so
$ dpkg -l | grep -E "^ii.*apache2"
ii apache2 2.4.29-1ubuntu4.27+esm7 amd64
ii apache2-bin 2.4.29-1ubuntu4.27+esm7 amd64
ii apache2-data 2.4.29-1ubuntu4.27+esm7 all
ii apache2-utils 2.4.29-1ubuntu4.27+esm7 amd64
$ apache2 -v
Server version: Apache/2.4.29 (Ubuntu)
Server built: 2026-05-21T10:22:30
$ ls -la /usr/lib/apache2/modules/mod_http2.so
-rw-r--r-- 1 root root 249376 May 21 12:22
/usr/lib/apache2/modules/mod_http2.so
md5: 08b51ec4fd4ae88d51583b5528fd2502
### 2. mod_http2.so references H2_MPLX_MSG as undefined
$ nm -D --undefined-only /usr/lib/apache2/modules/mod_http2.so | grep H2_
U H2_MPLX_MSG
### 3. NO binary or library shipped exports H2_MPLX_MSG
Searched /usr/sbin/apache2, all modules in /usr/lib/apache2/modules/,
libapr*, libaprutil*, libnghttp2*:
FOUND in: /usr/lib/apache2/modules/mod_http2.so
U H2_MPLX_MSG
(end of search)
The symbol is referenced but never defined anywhere on the system. This
is a build/link-time defect in the +esm7 build of mod_http2.so - it was
built against headers that declare H2_MPLX_MSG as an external symbol
that the server binary should export, but apache2-bin
2.4.29-1ubuntu4.27+esm7 does not export it.
## Workaround
sudo a2dismod -f http2
sudo systemctl start apache2
Restores service but disables HTTP/2 for all clients.
## Environment
$ lsb_release -a
Distributor ID: Ubuntu
Description: Ubuntu 18.04.6 LTS
Release: 18.04
Codename: bionic
$ uname -a
Linux tickets 4.15.0-248-generic #260-Ubuntu SMP Fri Mar 13 17:23:39 UTC
2026 x86_64
apache2-bin: 2.4.29-1ubuntu4.27+esm7
libapr1: 1.6.3-2ubuntu0.1~esm1
libaprutil1:1.6.1-2ubuntu0.1
libnghttp2: 1.30.0-1ubuntu1+esm3
## Severity / Impact
High for ESM customers: any bionic ESM host that picked up +esm7 via
unattended-upgrades and whose Apache was restarted after the upgrade has
been unreachable on ports 80/443 since. Confirmed on a production
OTRS/KIX deployment (university help-desk).
## Related
USN-7639-1 / USN-7639-2 (Apache HTTP Server vulnerabilities) - the +esm7
build originates from this advisory line. LP #2119395 fixed a separate
regression in mod_rewrite from the same patch series; this appears to be
a second, independent regression affecting mod_http2.
** Affects: apache2 (Ubuntu)
Importance: Undecided
Status: New
** Tags: bionic esm mod-http2 regression-update
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https://bugs.launchpad.net/bugs/2154546
Title:
apache2-bin 2.4.29-1ubuntu4.27+esm7 (bionic ESM): mod_http2.so has
undefined symbol H2_MPLX_MSG - apache2 fails to start
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