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CVE-2026-44433— Quicly is vulnerable to memory exhaustion

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 8b178e6之前版本存在资源管理错误漏洞，该漏洞源于对手可发送一个仅含一字节且在最大偏移量的STREAM帧以获取额外流量控制信用，在特定情况下可能导致拒绝服务；应用为存储乱序数据分配接收缓冲区时，对手仅发送少量数据包即可导致内存耗尽。

CVSS 5.3 · Medium EPSS 0.49% · P40

Possible ATT&CK Techniques 1 AI

T1499 · Endpoint Denial of Service

Affected Version Matrix 1

VendorProduct Version RangeStatus
h2o quicly < 8b178e6 affected
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I. Basic Information for CVE-2026-44433

Vulnerability Information
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Vulnerability Title
Quicly is vulnerable to memory exhaustion
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 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 circumstances could lead to a Denial of Service. Assuming the application prepares a receive buffer for storing all data that arrive out-of-order, up to the largest offset being received, this behavior could lead to the application allocating large amount of memory with the peer sending only a handful of packets, resulting in memory exhaustion. In addition to the receive buffer allocation strategy, the severity of this vulnerability depends on how the application controls the stream concurrency. In case of the H2O HTTP server, under its default setting, this bug increases the maximum amount of memory allocated per connection by about 4 times. This issue has been fixed by commit 8b178e6.
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
不加限制或调节的资源分配
Source: CVE Program / CVE List V5
Vulnerability Title
H2O quicly 资源管理错误漏洞
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 8b178e6之前版本存在资源管理错误漏洞，该漏洞源于对手可发送一个仅含一字节且在最大偏移量的STREAM帧以获取额外流量控制信用，在特定情况下可能导致拒绝服务；应用为存储乱序数据分配接收缓冲区时，对手仅发送少量数据包即可导致内存耗尽。
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 < 8b178e6 -

II. Public POCs for CVE-2026-44433

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III. Intelligence Information for CVE-2026-44433

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Patches & Fixes for CVE-2026-44433 (1)

Vendor Advisories for CVE-2026-44433 (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-2026-44434 5.3 MEDIUM Quicly is vulnerable to stateless reset injection

IV. Related Vulnerabilities

Same product: quicly
Same vendor: h2o
Same weakness: CWE-770

V. Comments for CVE-2026-44433

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