dbcve.org
Resource Allocation Without LimitsWeakness · CWE-770

CVE-2024-30156

HIGH · 7.5 CVSS v3.1 Published 2024-03-24
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
84/100
Remediation priority · High
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
Varnish Cache before 7.3.2 and 7.4.x before 7.4.3 (and before 6.0.13 LTS), and Varnish Enterprise 6 before 6.0.12r6, allows credits exhaustion for an HTTP/2 connection control flow window, aka a Broke Window Attack.

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

Varnish Cache and Varnish Enterprise contain a vulnerability where an attacker can exhaust HTTP/2 connection control flow window credits, known as a 'Broke Window Attack'. This resource exhaustion allows a malicious client to starve the connection of available flow control credits, preventing legitimate requests from being processed and potentially causing denial of service.

MitigationUpgrade to Varnish Cache 7.3.2, 7.4.3, 6.0.13 LTS, or Varnish Enterprise 6.0.12r6 or later. Monitor HTTP/2 connections for unusual flow control patterns as a temporary detection measure.

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

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
High

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

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. Verify Varnish is installed
    Run 'varnishd -V' to check if Varnish Cache or Varnish Enterprise is installed and get the version number
    Affected if Varnish is not installed - then not affected by this CVE
  2. Check installed Varnish version
    Run 'varnishd -V' and compare the output version to the fixed releases: Varnish Cache 7.3.2, 7.4.3, 6.0.13 LTS, or Varnish Enterprise 6.0.12r6
    Affected if Version is lower than the fixed releases for your edition (7.3.x < 7.3.2, 7.4.x < 7.4.3, 6.0.x < 6.0.13, or Enterprise < 6.0.12r6)
  3. Confirm HTTP/2 protocol support is enabled
    Check your Varnish configuration file (typically varnish.conf or vcl) for 'h2' parameter or HTTP/2 protocol enablement settings using 'varnishd -C' to see compiled VCL
    Affected if HTTP/2 is enabled in the Varnish configuration - the vulnerability only applies when HTTP/2 is active
  4. Monitor HTTP/2 flow control window depletion
    Use 'varnishstat -1' to check HTTP/2 connection metrics, specifically looking for patterns where client-side flow control credits remain exhausted or very low during normal operation
    Affected if Flow control window credits consistently stay at or near zero while legitimate client requests cannot be processed

You are affected if you are running a Varnish version lower than 7.3.2/7.4.3/6.0.13/6.0.12r6 AND HTTP/2 protocol support is enabled, allowing an attacker to exhaust HTTP/2 flow control credits.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade to Varnish Cache 7.3.2, 7.4.3, 6.0.13 LTS, or Varnish Enterprise 6.0.12r6 or later. Monitor HTTP/2 connections for unusual flow control patterns as a temporary detection measure.

Recommended fix High confidence

Varnish Cache 7.4.3+ / 7.3.2+ / 6.0.13+ (LTS), or Varnish Enterprise 6.0.12r6+

  1. 1. Identify current Varnish installation: Run 'varnishd -V' to determine exact version and whether it's open-source or Enterprise
  2. 2. For Varnish Cache 7.4.x: Upgrade to version 7.4.3 or later
  3. 3. For Varnish Cache 7.3.x: Upgrade to version 7.3.2 or later
  4. 4. For Varnish Cache 6.0.x (LTS): Upgrade to version 6.0.13 or later
  5. 5. For Varnish Enterprise 6: Upgrade to version 6.0.12r6 or later
  6. 6. After upgrade, restart the Varnish service: 'systemctl restart varnish' or 'service varnish restart'
  7. 7. Verify the new version is running and monitor for any configuration compatibility issues
Caveat Review release notes for minor version changes; custom VCL should remain compatible but test in staging first

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

Have this fixed Scoped from the published advisory
  • Consultation2.0 h
  • Implementation3.0 h
  • Testing3.0 h
  • Review / QA1.0 h
9.0 hours of engineering $1,570
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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-2024-30156 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