H2O

h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit edd7a120bfc4af11ac0cbebce2a43cc1f93f9af1, when h2o processes a QPACK instruction sent from the peer over HTTP/3, lib/http3/qpack.c might allocate an on-stack buffer as large as approximately 800 KB by calling alloca, which exceeds the default pthread stack size used by musl libc and causes the h2o server to crash with a segmentation fault while touching the guard page. This issue is fixed in commit edd7a120bfc4af11ac0cbebce2a43cc1f93f9af1.

Published: 2026-07-10T20:49:58.764Z
Updated: 2026-07-13T14:14:45.685Z

h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 9265bdd, there is an HTTP/2 state amplification issue that combines HPACK decompression amplification with Slowloris-style stream stalling. Amplified decoded header state can be retained by stalled HTTP/2 streams, and depending on the configuration, additional limits are needed to bound decoded header state and prevent attack. This issue has been fixed by commit 9265bdd.

Published: 2026-07-16T23:29:50.799Z
Updated: 2026-07-17T18:06:19.274Z

h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 6b5370d, h2o is vulnerable to a Denial of Service attack when calling alloca under certain conditions. When serving static files, h2o builds the file path on stack, by calling alloca. The maximum size of the memory allocated using alloca can be as huge as ~600KB, which exceeds the default pthread stack size used by musl libc (128KB). If the amount of memory allocated by alloca exceeds the stack size, the h2o server crashes with a segmentation fault, while it tries to touch the guard page. This issue has been fixed by commit 6b5370d.

Published: 2026-07-16T23:04:41.756Z
Updated: 2026-07-17T14:29:15.447Z

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.

Published: 2026-07-16T22:54:42.914Z
Updated: 2026-07-17T14:03:52.757Z

A weakness has been identified in h2oai h2o-3 up to 7402. This vulnerability affects the function exec of the file h2o-core/src/main/java/water/rapids/ast/prims/misc/AstSetProperty.java of the component Rapids setproperty Primitive Handler. Executing a manipulation can lead to improper access controls. The attack may be performed from remote. The exploit has been made available to the public and could be used for attacks. The vendor was contacted early about this disclosure but did not respond in any way.

Published: 2026-05-17T11:45:11.583Z
Updated: 2026-05-18T14:39:10.246Z