CVE-2020-10593
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 · uneditedTor before 0.3.5.10, 0.4.x before 0.4.1.9, and 0.4.2.x before 0.4.2.7 allows remote attackers to cause a Denial of Service (memory leak), aka TROVE-2020-004. This occurs in circpad_setup_machine_on_circ because a circuit-padding machine can be negotiated twice on the same circuit.
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 confidenceIn Tor's circuit padding implementation (circpad_setup_machine_on_circ), a logic flaw allows a circuit-padding machine to be negotiated twice on the same circuit. This causes a memory leak because the second negotiation allocates additional memory without properly releasing the first machine's resources, leading to eventual denial of service through memory exhaustion.
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>= 0.3.5, < 0.3.5.10> 0.4.1.0, < 0.4.1.9> 0.4.2.0, <= 0.4.2.7= 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.
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Check Tor version installedRun 'tor --version' or check the Tor package version using your system's package manager (dpkg -l tor, rpm -q tor, etc.)Affected if The installed version falls within any of these ranges: 0.3.5.x where x < 10, 0.4.1.x where x < 9, or 0.4.2.x where x <= 7 (but not 0.3.5.10+, 0.4.1.9+, or 0.4.2.8+)
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Confirm circuit padding is enabledCheck Tor configuration files (torrc) for 'CircuitPadding 1' or the default setting, and verify the tor process is running with padding enabledAffected if Circuit padding is enabled (the vulnerability only affects systems using Tor's circuit padding feature)
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Monitor for abnormal memory growthObserve the tor process memory usage over time using tools like 'ps aux | grep tor' or memory profiling tools; look for steadily increasing memory consumptionAffected if The tor process exhibits continuous memory growth without stabilization, potentially leading to memory exhaustion
You are affected if your Tor version is within the vulnerable ranges AND circuit padding is enabled, as the flaw allows double negotiation of the padding machine leading to memory leak.
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 data0.3.5.100.4.1.9
Upgrade Tor to version 0.3.5.10, 0.4.1.9, or 0.4.2.7 or later. Implement circuit state validation to ensure a padding machine cannot be registered twice on the same circuit.
- Consultation2.0 h
- Implementation1.0 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-2020-10593 — 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-2020-10593 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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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
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