dbcve.org
PrivoxyApplication

CVE-2021-20216

HIGH · 7.5 CVSS v3.1 Published 2021-03-25
Fix available
A fix is available. Upgrade to 3.0.31 or later.
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
A flaw was found in Privoxy in versions before 3.0.31. A memory leak that occurs when decompression fails unexpectedly may lead to a denial of service. The highest threat from this vulnerability is to system availability.

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

Privoxy before version 3.0.31 contains a memory leak that triggers when decompression fails unexpectedly. An attacker can cause the proxy to allocate memory without proper cleanup, eventually exhausting resources and causing a denial of service.

MitigationUpgrade Privoxy to version 3.0.31 or later. In the meantime, restrict or monitor decompression-heavy traffic to limit exposure.

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
PrivoxyApplication
Affected:< 3.0.31

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. Confirm Privoxy is installed
    Run 'which privoxy' or check for /usr/sbin/privoxy or /usr/local/sbin/privoxy
    Affected if Privoxy binary is not found on the system
  2. Identify installed Privoxy version
    Run 'privoxy --version' or 'privoxy -v'
    Affected if Version number returned is lower than 3.0.31 (e.g., 3.0.30, 3.0.28, etc.)
  3. Check for decompression-related configuration
    Inspect privoxy config files (usually in /etc/privoxy or /usr/local/etc/privoxy) for 'decompress', 'gunzip', or 'uncompress' directives
    Affected if Decompression handling is explicitly enabled in the configuration
  4. Verify gzip/deflate handling is active
    Check privoxy config for 'enable-proxy' and any 'filter' directives that process Accept-Encoding headers from clients
    Affected if Filters that process client-compressed content are enabled
  5. Monitor for memory growth patterns
    Observe privoxy process memory usage over time with tools like 'ps' or 'top', especially during decompression-heavy traffic
    Affected if Process memory continuously grows without stabilizing during normal proxy operations

Privoxy is affected only if installed version is below 3.0.31 AND decompression features are enabled in the configuration.

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.

From vendor data
Upgrade available Upgrade to 3.0.31 or later
Fixed in 3.0.31
Interim mitigation

Upgrade Privoxy to version 3.0.31 or later. In the meantime, restrict or monitor decompression-heavy traffic to limit exposure.

Fix this in Privoxy Scoped from the published advisory
  • Consultation3.0 h
  • Implementation2.0 h
  • Testing2.0 h
  • Review / QA1.0 h
8.0 hours of engineering $1,440
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,304.

Scan for this in your stack

Free · runs locally
dbcve dependency scanner

Check whether your project pulls in CVE-2021-20216 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.

Get it on GitHub Scan in the browser

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-2021-20216 in production — separate from our analysis above.

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.

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