CVE-2025-4820— Incorrect congestion window growth by optimistic ACK
Quick assessment
Affected
Cloudflare quiche
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.
quiche是Cloudflare开源的一个 IETF 指定的 QUIC 传输协议和 HTTP/3 的实现。 quiche存在安全漏洞，该漏洞源于拥塞窗口增长不当，可能导致数据发送速率超过路径支持能力。
Possible ATT&CK Techniques 1 AI
T1498.002 · Reflection Amplification
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I. Basic Information for CVE-2025-4820
Vulnerability Information
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Vulnerability Title
Incorrect congestion window growth by optimistic ACK
Source: CVE Program / CVE List V5
Vulnerability Description
Impact
Cloudflare quiche was discovered to be vulnerable to incorrect congestion window growth, which could cause it to send data at a rate faster than the path might actually support.
An unauthenticated remote attacker can exploit the vulnerability by first completing a handshake and initiating a congestion-controlled data transfer towards itself. Then, it could manipulate the victim's congestion control state by sending ACK frames exercising an opportunistic ACK attack; see RFC 9000 Section 21.4. The victim could grow the congestion window beyond typical expectations and allow more bytes in flight than the path might really support.
Patches
quiche 0.24.4 is the earliest version containing the fix for this issue.
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
quiche 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
quiche是Cloudflare开源的一个 IETF 指定的 QUIC 传输协议和 HTTP/3 的实现。 quiche存在安全漏洞，该漏洞源于拥塞窗口增长不当，可能导致数据发送速率超过路径支持能力。
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 |
|---|---|---|---|---|
| Cloudflare | quiche | <0.24.4 | - |
|
II. Public POCs for CVE-2025-4820
| # | POC Description | Source Link | Shenlong Link |
|---|
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IV. Related Vulnerabilities
Same product: quiche
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CVE-2026-12523
Resource exhaustion in quiche HTTP/3 and QPACK layers -
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CVE-2025-4821
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Same weakness: CWE-770
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V. Comments for CVE-2025-4820
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