CVE-2025-4820Public exploitNetwork attack vector

Unauthenticated resource exhaustion via optimistic ACKs

Published Jun 18, 2025 · Updated Jun 18, 2025

Resource exhaustion in Cloudflare quiche before 0.24.4 allows remote attackers to consume server CPU and bandwidth via optimistic QUIC ACK frames. The packet-number generator does not introduce unpredictable gaps, so guessed acknowledgments become delivery signals that inflate the congestion window. Exploitation requires a completed handshake and sustained server-to-client transfer; inflated sending can disrupt the server, its network, and competing connections.

CVSS severity5.3
Medium
EPSS probability0.80%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in Cloudflare quiche before 0.24.4 allows remote attackers to consume server CPU and bandwidth via optimistic QUIC ACK frames. The packet-number generator does not introduce unpredictable gaps, so guessed acknowledgments become delivery signals that inflate the congestion window. Exploitation requires a completed handshake and sustained server-to-client transfer; inflated sending can disrupt the server, its network, and competing connections.

The record

CVE
CVE-2025-4820
Published
Jun 18, 2025
Updated
Jun 18, 2025
Vendor
Cloudflare
Product
quiche
Classifications
CWE-770, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 18, 2025CVE publishedPublication date reported by the CVE source.
  2. Jun 18, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=<0.24.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Cloudflare · quicheversion=<0.24.4

Published CVSS scores

5.3Cloudflare, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
T1499.004Application or System Exploitation

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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