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Medium · 5.3 CVE-2025-4820 EUVD-2025-18652

Incorrect congestion window growth by optimistic ACK

Published Jun 18, 2025 · Updated Jun 18, 2025 · Assigned by cloudflare

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.

Affected products

VendorProductAffectedFixed
Cloudflare quiche <0.24.4 —

Fixed in Linux distributions

Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.

ReleasePackageFixed inAdvisory
Alpine v3.24 dnsdist 2.0.1-r0 —
Alpine v3.23 dnsdist 2.0.1-r0 —
Alpine v3.22 dnsdist 1.9.11-r0 —

References