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CVE-2026-44434— Quicly is vulnerable to stateless reset injection

Quick assessment

Affected
h2o quicly
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 quicly是H2O公司开源的一个 IETF QUIC 协议的实现。 H2O quicly dccf5d4之前版本存在安全漏洞，该漏洞源于缺少数据包条目验证，可能导致路径攻击者重置QUIC连接。

CVSS 5.3 · Medium EPSS 0.21% · P10

Possible ATT&CK Techniques 1 AI

T1499 · Endpoint Denial of Service

Affected Version Matrix 1

VendorProduct Version RangeStatus
h2o quicly < dccf5d4 affected
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I. Basic Information for CVE-2026-44434

Vulnerability Information
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Vulnerability Title
Quicly is vulnerable to stateless reset injection
Source: CVE Program / CVE List V5
Vulnerability Description
Quicly is an IETF QUIC protocol implementation intended primarily for use within the H2O HTTP server. Prior to commit dccf5d4, Quicly was vulnerable to stateless reset injection through lack of packet entry validation. The QUIC protocol is designed to withstand packet injection attacks, once the handshake is complete. Only packets that carry some secret patterns are considered as stateless resets. Quicly allows the peer to share up to 4 such patterns per connection. However, until now, it failed to determine which of the 4 slots that it uses to retain the secret patterns contains a valid entry. As the slots are zero-initialized, the failure meant that, unless the peer advertised 4 of such patterns, an all-zero pattern was treated as a stateless reset.In effect, this allowed an on-path attacker to reset QUIC connections governed by Quicly. This issue has been fixed by commit dccf5d4.
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:L
Source: CVE Program / CVE List V5
Vulnerability Type
对数据真实性的验证不充分
Source: CVE Program / CVE List V5
Vulnerability Title
H2O quicly 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
H2O quicly是H2O公司开源的一个 IETF QUIC 协议的实现。 H2O quicly dccf5d4之前版本存在安全漏洞，该漏洞源于缺少数据包条目验证，可能导致路径攻击者重置QUIC连接。
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 quicly < dccf5d4 -

II. Public POCs for CVE-2026-44434

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III. Intelligence Information for CVE-2026-44434

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Patches & Fixes for CVE-2026-44434 (1)

Vendor Advisories for CVE-2026-44434 (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-2026-44452 5.9 MEDIUM h2o is vulnerable to heap overrun
CVE-2026-44433 5.3 MEDIUM Quicly is vulnerable to memory exhaustion

IV. Related Vulnerabilities

Same product: quicly
Same vendor: h2o
Same weakness: CWE-345

V. Comments for CVE-2026-44434

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