CVE-2025-4820: Incorrect congestion window growth by optimistic ACK
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 Software
Event History
Frequently Asked Questions
What is the severity of CVE-2025-4820?
CVE-2025-4820 is classified as a high-severity vulnerability due to its potential to enable unauthorized data transmission rates that exceed network capacity.
How do I fix CVE-2025-4820?
To resolve CVE-2025-4820, update Cloudflare quiche to version 0.24.4 or later.
Who is affected by CVE-2025-4820?
CVE-2025-4820 affects users running Cloudflare quiche versions prior to 0.24.4.
What type of attacks can exploit CVE-2025-4820?
An unauthenticated remote attacker can exploit CVE-2025-4820 to disrupt network communications by sending data too quickly.
What is the impact of CVE-2025-4820?
The impact of CVE-2025-4820 includes potential denial-of-service conditions due to incorrect congestion control.