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CVE-2025-4821— Incorrect congestion window growth by invalid ACK ranges

Quick assessment

Affected
Cloudflare quiche
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.

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正确，可能导致发送数据速率超过路径实际支持能力。

CVSS 7.5 · High EPSS 0.83% · P54

Possible ATT&CK Techniques 1 AI

T1498 · Network Denial of Service
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I. Basic Information for CVE-2025-4821

Vulnerability Information
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Vulnerability Title
Incorrect congestion window growth by invalid ACK ranges
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 covering a large range of packet numbers (including packet numbers that had never been sent); see RFC 9000 Section 19.3. The victim could grow the congestion window beyond typical expectations and allow more bytes in flight than the path might really support. In extreme cases, the window might grow beyond the limit of the internal variable's type, leading to an overflow panic. 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:H
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正确，可能导致发送数据速率超过路径实际支持能力。
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-2025-4821

# POC Description Source Link Shenlong Link
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Qwen3.6-35B-A3B · 9892 chars
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III. Intelligence Information for CVE-2025-4821

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IV. Related Vulnerabilities

Same product: quiche
Same vendor: Cloudflare
Same weakness: CWE-770

V. Comments for CVE-2025-4821

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