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...

EUVD-2026-45069

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...

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...

CVE-2026-44433

CVE-2026-44433 concerns the Quicly QUIC implementation (used with H2O HTTP server). Before commit 8b178e6, an adversarial peer could send a STREAM frame with a single byte at the largest permitted offset to obtain additional flow control credit, potentially causing a denial of service. If the app...

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...

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...

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 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...

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...

PYSEC-2026-1441 H2O Vulnerable to Arbitrary File Overwrite

In h2oai/h2o-3 version 3.46.0, the /99/Models/name/json endpoint allows for arbitrary file overwrite on the target server. The vulnerability arises from the exportModelDetails function in ModelsHandler.java, where the user-controllable mexport.dir parameter is used to specify the file path for...

H2O Vulnerable to Denial of Service (DoS) via `/3/ImportFiles` Endpoint

A vulnerability in the /3/ImportFiles endpoint of h2oai/h2o-3 version 3.46.1 allows an attacker to cause a denial of service. The endpoint takes a single GET parameter, path, which can be recursively set to reference itself. This leads the server to repeatedly call its own endpoint, eventually...

PYSEC-2026-1438 H2O Vulnerable to Denial of Service (DoS) via `HEAD` Request

A vulnerability in the typeahead endpoint of h2oai/h2o-3 version 3.46.0 allows for a denial of service. The endpoint performs a HEAD request to verify the existence of a specified resource without setting a timeout. An attacker can exploit this by sending multiple requests to an attacker-controll...

H2O Vulnerable to Denial of Service (DoS) via `HEAD` Request

A vulnerability in the typeahead endpoint of h2oai/h2o-3 version 3.46.0 allows for a denial of service. The endpoint performs a HEAD request to verify the existence of a specified resource without setting a timeout. An attacker can exploit this by sending multiple requests to an attacker-controll...

PYSEC-2026-1443 H2O Vulnerable to Denial of Service (DoS) via `/3/ImportFiles` Endpoint

A vulnerability in the /3/ImportFiles endpoint of h2oai/h2o-3 version 3.46.1 allows an attacker to cause a denial of service. The endpoint takes a single GET parameter, path, which can be recursively set to reference itself. This leads the server to repeatedly call its own endpoint, eventually...

H2O Vulnerable to Denial of Service (DoS) via Large GZIP Parsing

In h2oai/h2o-3 version 3.46.0.2, a vulnerability exists where uploading and repeatedly parsing a large GZIP file can cause a denial of service. The server becomes unresponsive due to memory exhaustion and a large number of concurrent slow-running jobs. This issue arises from the improper handling...

PYSEC-2026-1439 H2O Vulnerable to Denial of Service (DoS) via Large GZIP Parsing

In h2oai/h2o-3 version 3.46.0.2, a vulnerability exists where uploading and repeatedly parsing a large GZIP file can cause a denial of service. The server becomes unresponsive due to memory exhaustion and a large number of concurrent slow-running jobs. This issue arises from the improper handling...

H2O Vulnerable to Arbitrary File Overwrite via File Export

In h2oai/h2o-3 version 3.46.0, the endpoint for exporting models does not restrict the export location, allowing an attacker to export a model to any file in the server's file structure, thereby overwriting it. This vulnerability can be exploited to overwrite any file on the target server with a...