Skip to content
Fencer Vulns
high 7.5

CVE-2025-4821 json

Incorrect congestion window growth by invalid ACK ranges

published 2025-06-18 16 mo ago modified 2026-06-17 4 mo ago also EUVD-2025-18651

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.0%
EPSS 1.0% chance of exploitation in 30 days, percentile 62%
public exploits
0
none known

Summary

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.

Patch / fix

  • cloudflare quiche 0.24.4
  • dnsdist Alpine 3.22 1.9.11-r0
  • dnsdist Alpine 3.24, Alpine 3.23 2.0.1-r0

alpine advisories ALPINE-CVE-2025-4821

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
16 mo ago

Exploit prediction

0.98% chance of exploitation in the next 30 days, higher than 62% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

  • Cloudflare quiche

Classification

Weakness
  • CWE-770 Allocation of Resources Without Limits or Throttling

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.