CVE-2025-4820

Incorrect congestion window growth by optimistic ACK

Published Jun 18, 2025 CVSS 3.1 · 5.3 Medium EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
EUVD EUVD EUVD-2025-18652 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.
History
Type Values Removed Values Added
CPEs cpe:2.3:a:cloudflare:quiche:*:*:*:*:*:rust:*:*
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
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.
Title Incorrect congestion window growth by optimistic ACK
Weaknesses CWE-770
References
Metrics cvssV3_1

{'score': 5.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
cloudflare
Published
Updated
Jun 18, 2025, 6:27 PM
Reserved
May 16, 2025, 11:52 AM
Status
Analyzed
Published
Jun 18, 2025, 4:15 PM
Modified
Jun 17, 2026, 9:34 AM