Cloudflare quiche up to 0.24.3 Congestion Window Growth allocation of resources

Summaryinfo

A vulnerability was found in Cloudflare quiche up to 0.24.3. It has been classified as critical. This affects an unknown part of the component Congestion Window Growth. Performing a manipulation results in allocation of resources. This vulnerability is reported as CVE-2025-4821. The attack is possible to be carried out remotely. No exploit exists. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability classified as critical has been found in Cloudflare quiche up to 0.24.3. This affects an unknown code block of the component Congestion Window Growth. The manipulation with an unknown input leads to a allocation of resources vulnerability. CWE is classifying the issue as CWE-770. The product allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor. This is going to have an impact on availability. The summary by CVE is:

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.

It is possible to read the advisory at github.com. This vulnerability is uniquely identified as CVE-2025-4821 since 05/16/2025. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. The technical details are unknown and an exploit is not publicly available. The attack technique deployed by this issue is T1499 according to MITRE ATT&CK.

Upgrading to version 0.24.4 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2025-18651). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Productinfo

Type

• Cloud Software

Vendor

• Cloudflare

Name

• quiche

Version

• 0.24.0
• 0.24.1
• 0.24.2
• 0.24.3

Website

• Product: https://github.com/cloudflare/quiche/

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Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

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