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

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 6b5370d之前版本存在资源管理错误漏洞，该漏洞源于调用alloca时超过默认栈大小，当处理静态文件时在栈上构建文件路径，可能导致拒绝服务攻击。

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 < 6b5370d affected
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I. Basic Information for CVE-2026-44453

Vulnerability Information
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Vulnerability Title
h2o is vulnerable to musl libc stack overflow
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 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.
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 6b5370d之前版本存在资源管理错误漏洞，该漏洞源于调用alloca时超过默认栈大小，当处理静态文件时在栈上构建文件路径，可能导致拒绝服务攻击。
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 < 6b5370d -

II. Public POCs for CVE-2026-44453

# POC Description Source Link Shenlong Link
AI-Generated POC Premium
Qwen3.6-35B-A3B · 7046 chars
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Vulnerability reproduction recording (real sandbox build + trigger, exclusive)
In-depth vulnerability mechanism
Trigger conditions & impact
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Exploit chain & mitigation
POC zip download
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III. Intelligence Information for CVE-2026-44453

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Patches & Fixes for CVE-2026-44453 (1)

Vendor Advisories for CVE-2026-44453 (1)

Same Patch Batch · h2o · 2026-07-16 · 7 CVEs total

CVE-2026-44436 7.5 HIGH Quicly is vulnerable to connection state corruption
CVE-2026-44435 7.5 HIGH Quicly: Remote Denial of Service via assertion failure when CRYPTO stream handshake data e
CVE-2026-54340 7.5 HIGH h2o has HTTP/2 state amplification
CVE-2026-44452 5.9 MEDIUM h2o is vulnerable to heap overrun
CVE-2026-44433 5.3 MEDIUM Quicly is vulnerable to memory exhaustion
CVE-2026-44434 5.3 MEDIUM Quicly is vulnerable to stateless reset injection

IV. Related Vulnerabilities

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

V. Comments for CVE-2026-44453

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