| Name | CVE-2026-44452 |
| Description | h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 8dc37cb, when h2o receives a ClientHello message over TLS or QUIC and it contains a zero-length SNI extension, the h2o server runs over the zero-length hostname while trying to copy the hostname, assuming that it is NULL-terminated. This is a potential denial-of-service attack vector in sense that it might trigger segmentation violation. This issue has been fixed by commit 8dc37cb. |
| Source | CVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more) |
Vulnerable and fixed packages
The table below lists information on source packages.
| Source Package | Release | Version | Status |
|---|
| h2o (PTS) | bullseye | 2.2.5+dfsg2-6 | vulnerable |
| bookworm | 2.2.5+dfsg2-7 | vulnerable |
The information below is based on the following data on fixed versions.
| Package | Type | Release | Fixed Version | Urgency | Origin | Debian Bugs |
|---|
| h2o | source | (unstable) | (unfixed) | | | |
Notes
[bookworm] - h2o <postponed> (Minor issue, DoS; bundled picotls client_hello_decode_server_name() accepts a zero-length SNI hostname, and on_client_hello_ptls() then calls ptls_set_server_name() which strlen()s the non-terminated ClientHello buffer)
[bullseye] - h2o <postponed> (Minor issue, DoS; bundled picotls client_hello_decode_server_name() accepts a zero-length SNI hostname, and on_client_hello_ptls() then calls ptls_set_server_name() which strlen()s the non-terminated ClientHello buffer)
https://github.com/h2o/h2o/security/advisories/GHSA-w68q-rqwx-7wvq
Fixed by (merge): https://github.com/h2o/h2o/commit/8dc37cb1e6171f7f772667618ea440696fed82c3