How to fix CVE-2025-4820?

Within 30 days: Identify affected systems and apply vendor patches as part of regular patch cycle. Monitor vendor channels for patch availability.

Is Quiche affected by CVE-2025-4820?

Organizations using Impact Cloudflare quiche should be aware of moderate risk from CVE-2025-4820 rated CVSS 5.3. Exploitation could compromise the security of affected deployments. Organizations should apply vendor updates when available and monitor for exploitation.

CVE-2025-4820

EUVD-2025-18652 MEDIUM

2025-06-18 [email protected]

5.3

CVSS 3.1

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

Low

Lifecycle Timeline

EUVD ID Assigned

Mar 14, 2026 - 22:49 euvd

EUVD-2025-18652

Analysis Generated

Mar 14, 2026 - 22:49 vuln.today

CVE Published

Jun 18, 2025 - 16:15 nvd

MEDIUM 5.3

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.

Analysis

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.

Technical Context

A denial of service vulnerability allows an attacker to disrupt the normal functioning of a system, making it unavailable to legitimate users. This vulnerability is classified as Allocation of Resources Without Limits or Throttling (CWE-770).

Affected Products

Affected products: Cloudflare Quiche

Remediation

Implement rate limiting and input validation. Use timeout mechanisms for resource-intensive operations. Deploy DDoS protection where applicable.

Priority Score

Low Medium High Critical

KEV: 0

EPSS: +0.3

CVSS: +26

POC: 0

Vendor Status

Debian

Bug #841848

quiche

Release	Status	Fixed Version	Urgency
	open	-	-

CVE-2025-4820 vulnerability details – vuln.today

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CVE-2025-4820

CVSS Vector

Lifecycle Timeline

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Description

Analysis

Technical Context

Affected Products

Remediation

Priority Score

Vendor Status

Debian

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CVE-2025-4820

CVSS Vector

Lifecycle Timeline

Tags

Description

Analysis

Technical Context

Affected Products

Remediation

Priority Score

Vendor Status

Debian

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External POC / Exploit Code