High severity · published Jun 18, 2025
CVE-2025-4821
Incorrect congestion window growth by invalid ACK ranges
7.5
CVSS
0.9%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.9% · higher than 61% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
QU
quiche · Cloudflare
<0.24.4 · source: vendor, NVD
Affected product
QU
quiche
Cloudflare
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