Vulnerability · Published Jun 18, 2025 · Assigned by cloudflare
CVE-2025-4820Incorrect congestion window growth by optimistic ACK
Medium 5.3
In plain English
A medium-severity resource allocation without limits in quiche from Cloudflare. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.9% (higher than 59% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine:v3.22 | dnsdist | 1.9.11-r0 | ALPINE-CVE-2025-4820 |
| Alpine:v3.23 | dnsdist | 2.0.1-r0 | ALPINE-CVE-2025-4820 |
| Alpine:v3.24 | dnsdist | 2.0.1-r0 | ALPINE-CVE-2025-4820 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Cloudflare | quiche | <0.24.4 |
Weakness: CWE-770 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L