Debian LinuxOperating system · Debian
CVE-2020-11653
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 6.0.6 LTS, 6.1.x and 6.2.x before 6.2.3, and 6.3.x before 6.3.2. It occurs when communication with a TLS termination proxy uses PROXY version 2. There can be an assertion failure and daemon restart, which causes a performance loss.
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 · moderate confidenceVarnish Cache before 6.0.6 LTS, 6.2.3, and 6.3.2 contains a bug in PROXY protocol version 2 handling when used with TLS termination proxies. A specific condition in the PROXY v2 communication triggers an assertion failure, causing the Varnish daemon to restart. This results in denial of service through performance loss and service interruption.
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
Debian LinuxOperating system
= 10.0>= 6.1.0, < 6.2.3>= 6.3.0, < 6.3.2>= 6.0.0, < 6.0.6= 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
- 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 checksWork through these to decide whether this CVE applies to you.
-
Check installed Varnish versionRun `varnishd -V` or `varnishd -v` to display the Varnish daemon versionAffected if The version shown is any of: 6.0.0 through 6.0.5, 6.1.0 through 6.2.2, or 6.3.0 through 6.3.1 (these fall within the affected ranges)
-
Verify PROXY protocol v2 is enabledInspect Varnish configuration files (typically in /etc/varnish/ or as specified in -f argument) and search for 'proxy' or 'proxyv2' in backend or listen declarationsAffected if PROXY protocol version 2 is explicitly configured or enabled in the VCL configuration
-
Confirm TLS termination proxy is in useExamine the architecture: check if a TLS termination proxy (such as nginx, haproxy, or similar) sits in front of Varnish and sends PROXY protocol headersAffected if A TLS termination proxy is configured to handle TLS and forward connections to Varnish using PROXY protocol v2
-
Identify the specific vulnerable combinationCross-reference: if Varnish version is affected AND PROXY v2 is enabled AND a TLS termination proxy forwards PROXY v2 headers to Varnish, the condition is metAffected if All three conditions are true: affected Varnish version, PROXY v2 enabled, and TLS termination proxy using PROXY v2 with Varnish
You are affected only if your Varnish version is in the vulnerable range AND you have PROXY protocol v2 enabled AND a TLS termination proxy forwards PROXY v2 headers to Varnish.
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 data6.0.66.2.36.3.2
Upgrade Varnish Cache to version 6.0.6 LTS, 6.2.3, or 6.3.2 (whichever matches the installed branch). If immediate upgrade is not possible, avoid using PROXY protocol version 2 with TLS termination proxies until patching can be completed.
Fix this in Debian Linux
Scoped from the published advisory
- Consultation1.0 h
- Implementation2.0 h
- Testing2.0 h
- Review / QA1.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $1,664.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2020-11653 — 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-2020-11653 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
Be the first to add a field note for this CVE — a mitigation you’ve verified, a version caveat, or a link to a working fix. Sign in above to contribute.
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.
- 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