CVE-2019-20637
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 · uneditedAn issue was discovered in Varnish Cache before 6.0.5 LTS, 6.1.x and 6.2.x before 6.2.2, and 6.3.x before 6.3.1. It does not clear a pointer between the handling of one client request and the next request within the same connection. This sometimes causes information to be disclosed from the connection workspace, such as data structures associated with previous requests within this connection or VCL-related temporary headers.
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 confidenceVarnish Cache fails to clear a pointer between handling consecutive client requests within the same connection. This causes data from previous requests (including VCL temporary headers and connection workspace data) to potentially leak into subsequent requests, resulting in information disclosure.
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>= 6.1.0, < 6.2.2>= 6.3.0, < 6.3.1>= 6.0.0, < 6.0.5= 15.0= 15.1CVSS 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
- High
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
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 checksWork through these to decide whether this CVE applies to you.
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Identify installed Varnish versionRun `varnishd -V` or check package manager output (e.g., `rpm -q varnish`, `dpkg -l varnish`)Affected if Version is 6.0.0-6.0.4, 6.1.0-6.2.1, or 6.3.0
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Confirm Varnish service is runningRun `varnishd -V` or check process status with `ps aux | grep varnish`Affected if Varnish is running any affected version listed above
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Verify HTTP keep-alive is enabled (default behavior)Check VCL configuration with `varnishd -C` or inspect varnishd startup options; look for `keepalive_timeout` or `http_keepalive` settings in VCL or command lineAffected if Keep-alive connections are allowed (default), as the vulnerability only triggers between consecutive requests within the same connection
You are affected if Varnish version is 6.0.0-6.0.4, 6.1.0-6.2.1, or 6.3.0 and keep-alive connections are enabled (default), allowing potential data leakage between consecutive requests in the same connection.
Generated from the published advisory. Verify against your own configuration.
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.
From vendor data6.0.56.2.26.3.1
Upgrade Varnish Cache to version 6.0.5 LTS, 6.2.2, or 6.3.1 or later to patch the memory handling vulnerability.
- Consultation4.0 h
- Implementation2.0 h
- Testing4.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2019-20637 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2019-20637 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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