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

Quick assessment

Affected
h2o h2o
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

h2o是H2O公司开源的一款新一代HTTP服务器。 h2o存在资源管理错误漏洞，该漏洞源于当处理HTTP/3对端发送的QPACK指令时，lib/http3/qpack.c可能通过alloca分配约800KB的栈上缓冲区，超出musl libc默认pthread栈大小，导致触碰保护页时服务崩溃。

CVSS 7.5 · High EPSS 0.49% · P40

Possible ATT&CK Techniques 1 AI

T1499 · Endpoint Denial of Service

Affected Version Matrix 1

VendorProduct Version RangeStatus
h2o h2o < edd7a120bfc4af11ac0cbebce2a43cc1f93f9af1 affected
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I. Basic Information for CVE-2026-55213

Vulnerability Information
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Vulnerability Title
h2o: musl libc stack overflow (QPACK)
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
未经控制的内存分配
Source: CVE Program / CVE List V5
Vulnerability Title
h2o 资源管理错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
h2o是H2O公司开源的一款新一代HTTP服务器。 h2o存在资源管理错误漏洞，该漏洞源于当处理HTTP/3对端发送的QPACK指令时，lib/http3/qpack.c可能通过alloca分配约800KB的栈上缓冲区，超出musl libc默认pthread栈大小，导致触碰保护页时服务崩溃。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
h2o h2o < edd7a120bfc4af11ac0cbebce2a43cc1f93f9af1 -

II. Public POCs for CVE-2026-55213

# POC Description Source Link Shenlong Link
AI-Generated POC Premium
Qwen3.6-35B-A3B · 8169 chars
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Vulnerability reproduction recording (real sandbox build + trigger, exclusive)
In-depth vulnerability mechanism
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Exploit chain & mitigation
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III. Intelligence Information for CVE-2026-55213

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Patches & Fixes for CVE-2026-55213 (1)

Vendor Advisories for CVE-2026-55213 (1)

IV. Related Vulnerabilities

Same product: h2o
Same vendor: h2o
Same weakness: CWE-789

V. Comments for CVE-2026-55213

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