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CVE-2026-44452— h2o is vulnerable to heap overrun

Quick assessment

Affected
h2o h2o
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
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 8dc37cb之前版本存在缓冲区错误漏洞，该漏洞源于在处理TLS或QUIC的ClientHello消息时，若包含零长度的SNI扩展，服务器在复制主机名时假定其以NULL结尾，可能导致分段违规，从而引发拒绝服务攻击。

CVSS 5.9 · Medium EPSS 0.41% · P33

Possible ATT&CK Techniques 1 AI

T1499 · Endpoint Denial of Service

Affected Version Matrix 1

VendorProduct Version RangeStatus
h2o h2o < 8dc37cb affected
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I. Basic Information for CVE-2026-44452

Vulnerability Information
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Vulnerability Title
h2o is vulnerable to heap overrun
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 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
跨界内存读
Source: CVE Program / CVE List V5
Vulnerability Title
H2O 缓冲区错误漏洞
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 8dc37cb之前版本存在缓冲区错误漏洞，该漏洞源于在处理TLS或QUIC的ClientHello消息时，若包含零长度的SNI扩展，服务器在复制主机名时假定其以NULL结尾，可能导致分段违规，从而引发拒绝服务攻击。
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 < 8dc37cb -

II. Public POCs for CVE-2026-44452

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III. Intelligence Information for CVE-2026-44452

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Vendor Advisories for CVE-2026-44452 (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-2026-44453 7.5 HIGH h2o is vulnerable to musl libc stack overflow
CVE-2026-54340 7.5 HIGH h2o has HTTP/2 state amplification
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-125

V. Comments for CVE-2026-44452

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