CVE-2025-4821

Incorrect congestion window growth by invalid ACK ranges

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.

Category

7.5
CVSS
Severity: High
CVSS 3.1 •
EPSS 0.08%
Affected: Cloudflare quiche
Published at:
Updated at:

References

Frequently Asked Questions

What is the severity of CVE-2025-4821?
CVE-2025-4821 has been scored as a high severity vulnerability.
How to fix CVE-2025-4821?
To fix CVE-2025-4821, make sure you are using an up-to-date version of the affected component(s) by checking the vendor release notes. As for now, there are no other specific guidelines available.
Is CVE-2025-4821 being actively exploited in the wild?
As for now, there are no information to confirm that CVE-2025-4821 is being actively exploited. According to its EPSS score, there is a ~0% probability that this vulnerability will be exploited by malicious actors in the next 30 days.
What software or system is affected by CVE-2025-4821?
CVE-2025-4821 affects Cloudflare quiche.
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