dbcve.org
QuicheApplication · Cloudflare

CVE-2025-4820

MEDIUM · 5.3 CVSS v3.1 Published 2025-06-18
Fix available
A fix is available. Upgrade to 0.24.4 or later.
See remediation →
62/100
Remediation priority · Elevated
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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 summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Cloudflare quiche contains a congestion control vulnerability where incorrect window growth allows an authenticated attacker (after completing a handshake) to manipulate the victim's congestion control state via ACK frames in an opportunistic ACK attack (RFC 9000 Section 21.4). This causes the victim to grow its congestion window beyond normal expectations and send data at rates the network path cannot support, potentially leading to packet loss, latency spikes, or denial of service.

MitigationUpgrade quiche to version 0.24.4 or later to obtain the fix for the incorrect congestion window growth.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
QuicheApplication
Affected:< 0.24.4

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Locate quiche library in your environment
    Search for quiche library files or check your application's dependency manifest (e.g., Cargo.lock for Rust projects, package.json for Node.js, or library search commands like 'find / -name "*quiche*"' or 'ldconfig -p | grep quiche')
    Affected if quiche library is present in your environment
  2. Identify installed quiche version
    Run version check command appropriate to your environment: for Rust projects check Cargo.lock for quiche version, for system libraries use 'pkg-config --modversion quiche' or check library file metadata
    Affected if version cannot be determined or is lower than 0.24.4
  3. Compare your version against the affected range
    Verify the installed quiche version number against the affected range: any version below 0.24.4 is vulnerable
    Affected if installed version is less than 0.24.4
  4. Confirm QUIC connections are being handled
    Review application logs, configuration, or network captures to confirm the application uses quiche for QUIC protocol handling (vulnerability only applies when quiche processes QUIC traffic)
    Affected if application processes QUIC connections using quiche and version is below 0.24.4

You are affected if your environment uses Cloudflare quiche library version below 0.24.4 for processing QUIC connections.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 0.24.4 or later
Fixed in 0.24.4
Interim mitigation

Upgrade quiche to version 0.24.4 or later to obtain the fix for the incorrect congestion window growth.

Recommended fix High confidence

quiche 0.24.4 or later

  1. Identify the current version of quiche in use by checking project dependencies or cargo/Cargo.toml
  2. Upgrade quiche to version 0.24.4 or later
  3. Verify the upgrade was successful by checking the installed version
  4. Test the application to ensure the QUIC connection functionality remains intact after the upgrade

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Quiche Scoped from the published advisory
  • Consultation4.0 h
  • Implementation2.0 h
  • Testing8.0 h
  • Review / QA4.0 h
18.0 hours of engineering $3,080
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $4,928.

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2025-4820 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data