CVE-2020-15572
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 0.4.3.6 has an out-of-bounds memory access that allows a remote denial-of-service (crash) attack against Tor instances built to use Mozilla Network Security Services (NSS), aka TROVE-2020-001.
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 confidenceTor before 0.4.3.6 contains an out-of-bounds memory access vulnerability in its integration with Mozilla Network Security Services (NSS). A remote attacker can trigger this memory safety flaw to cause a denial-of-service via crash. Only Tor instances built with NSS are affected.
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< 0.3.5.11> 0.4.2.0, < 0.4.2.8> 0.4.3.0, < 0.4.3.6= 0.4.4.0= 0.4.4.1CVSS 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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Verify Tor installationRun 'tor --version' or check for tor package via package manager (dpkg -l tor, rpm -qa tor, etc.)Affected if Tor is not installed - not affected
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Identify Tor versionRun 'tor --version' and parse the version number from the outputAffected if Version matches < 0.3.5.11; > 0.4.2.0 through < 0.4.2.8; > 0.4.3.0 through < 0.4.3.6; = 0.4.4.0; or = 0.4.4.1 - potentially affected
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Determine if Tor was built with NSSCheck Tor compile-time configuration: run 'tor --build-info' or inspect tor binary with 'ldd tor' for libnss3.so, or check build documentation/configAffected if Tor binary links against NSS libraries (libnss3, libnssckbi) - vulnerable condition present; if built with OpenSSL only - not affected
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Confirm running Tor processCheck for active tor processes: 'ps aux | grep tor' or 'systemctl status tor'Affected if Tor process is running with NSS-linked binary and vulnerable version - actively exploitable
You are affected if a Tor instance built with NSS is running a version matching the affected ranges listed, as only NSS-integrated builds contain this out-of-bounds flaw.
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 data0.3.5.110.4.2.80.4.3.6
Upgrade Tor to version 0.4.3.6 or later. Identify any Tor relays or clients using NSS and prioritize their updates, as the vulnerability is remotely exploitable for crash attacks.
- Consultation4.0 h
- Implementation3.0 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-2020-15572 — 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-2020-15572 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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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