5.3

CVE-2025-4820: cloudflare quiche

CVSS: 5.3v3.1MediumAnalyzed
Published 18-06-2025Last modified 18-06-2025
Open JSON

Vulnerability summary

CVE-2025-4820 is a medium (CVSS 5.3) vulnerability in cloudflare quiche. EPSS estimates a 0.86% chance of exploitation in the next 30 days, higher than 57.9% of scored vulnerabilities.

Overall risk
21/100
0100
Low · default modelHow is this calculated?
CVSS score
5.3/10
010
Medium · v3.1 (CVE.org)
EPSS score
0.86%
0%100%
Low · 0.00 pp in 30 days
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded

Timeline

  1. 18-06-2025
    PublishedVulnerability first disclosed.
  2. 18-06-2025
    Last modifiedVulnerability information updated.

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 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.

CVSS metrics

2 scores · 2 sources · 1 version

EPSS trend

Probability

0.86%

Chance of exploitation in the next 30 days

Percentile

58%

Versus all other CVEs

30-day change

0.00 pp

From 0.86% on 19-09-2026

19-09-202619-10-2026
EPSS score
0.86%

Known exploited

Compare KEV catalogs

Not in any of the 3 tracked catalogs.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Cloudflare1 product

1 vendor · 1 product

References

1 links