H2O ImportFiles - Local File Inclusion

An attacker is able to read any file on the server hosting the H2O dashboard without any authentication. id: CVE-2023-6038 info: name: H2O ImportFiles - Local File Inclusion author: danmcinerney,byt3bl33d3r severity: high description: | An attacker is able to read any file on the server hosting t...

Linux Distros Unpatched Vulnerability : CVE-2026-44453

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available. - 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...

Linux Distros Unpatched Vulnerability : CVE-2026-44452

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available. - 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...

CVE-2026-54340 h2o has HTTP/2 state amplification

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,...

CVE-2026-54340 h2o has HTTP/2 state amplification

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,...

CVE-2026-44453

The CVE-2026-44453 entry concerns the h2o HTTP server (HTTP/1.x, HTTP/2, HTTP/3). Before commit 6b5370d, h2o could trigger a Denial of Service by calling alloca to build file paths for static files, potentially allocating up to ~600 KB on the stack. This exceeds the musl libc pthread stack defaul...

CVE-2026-44453 h2o is vulnerable to musl libc stack overflow

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 memor...

CVE-2026-44453 h2o is vulnerable to musl libc stack overflow

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 memor...

CVE-2026-44452 h2o is vulnerable to heap overrun

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 ...

CVE-2026-44452

CVE-2026-44452 affects the h2o HTTP server (supports HTTP/1.x, 2, 3). Affected behavior occurs when a TLS/QUIC ClientHello contains a zero-length SNI extension; h2o can attempt to copy the hostname assuming NULL-termination, causing a heap/segmentation fault that may enable a denial-of-service. T...

CVE-2026-44452 h2o is vulnerable to heap overrun

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 ...

CVE-2026-44433

CVE-2026-44433 affects the Quicly QUIC protocol implementation used with the H2O HTTP server. Prior to commit 8b178e6, an adversarial peer could send a STREAM frame carrying only a single byte at the largest permitted offset to obtain additional flow control credit, potentially causing memory exh...

CVE-2026-44433 Quicly is vulnerable to memory exhaustion

Quicly is an IETF QUIC protocol implementation intended primarily for use within the H2O HTTP server. Prior to commit 8b178e6, an adversarial peer could send a STREAM frame carrying just one byte at the largest offset being permitted to obtain additional flow control credit, which under certain...

PT-2026-60600

Name of the Vulnerable Software and Affected Versions Quicly versions prior to commit dccf5d4 Description Quicly, an IETF QUIC protocol implementation used in the H2O HTTP server, is susceptible to stateless reset injection. The issue stems from a lack of packet entry validation when handling...

PT-2026-60592

Name of the Vulnerable Software and Affected Versions Quicly versions prior to commit 8b178e6 Description An adversarial peer can trigger a Denial of Service by sending a STREAM frame containing a single byte at the maximum permitted offset to obtain additional flow control credit. If the...

Linux Distros Unpatched Vulnerability : CVE-2026-55213

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available. - 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...

UBUNTU-CVE-2026-55213

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...

CVE-2026-55213

CVE-2026-55213 (h2o HTTP server) – Affected component: lib/http3/qpack.c, invoked while processing a QPACK instruction over HTTP/3. Root cause: on-stack allocation of a large buffer (up to ~800 KB) via alloca, exceeding default musl libc pthread stack size, leading to a segmentation fault when to...

CVE-2026-55213 h2o: musl libc stack overflow (QPACK)

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...

CVE-2026-55213

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...