CVE-2021-34550
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 Tor before 0.4.6.5, aka TROVE-2021-006. The v3 onion service descriptor parsing allows out-of-bounds memory access, and a client crash, via a crafted onion service descriptor
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 confidenceA memory safety vulnerability in Tor's v3 onion service descriptor parser allows out-of-bounds memory access when parsing a crafted malicious descriptor, leading to client crash. The issue stems from insufficient bounds checking during descriptor parsing in versions before 0.4.6.5.
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< 0.3.5.15>= 0.4.0.0, < 0.4.4.9>= 0.4.5.0, < 0.4.5.9>= 0.4.6.0, < 0.4.6.5CVSS 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 installed Tor versionRun `tor --version` or check via package manager (e.g., `dpkg -l | grep tor`, `rpm -q tor`)Affected if Version output is missing or falls within < 0.3.5.15, >= 0.4.0.0 and < 0.4.4.9, >= 0.4.5.0 and < 0.4.5.9, or >= 0.4.6.0 and < 0.4.6.5
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Confirm v3 onion service is in useInspect torrc for `ClientOnionAuthDir`, `HidServAuth` directives, or check for presence of v3 onion service private keys in the data directory (files ending in `.onion` with uppercase letters)Affected if Tor is configured to use v3 onion services or acts as a client receiving v3 descriptors
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Verify descriptor acceptance pathCheck if Tor accepts incoming or parses external onion service descriptors, typically default for clients connecting to v3 onion servicesAffected if Tor acts as a client connecting to v3 onion services (not just a relay) and parses received descriptors
User is affected if Tor version is in any of the affected ranges AND the Tor process parses v3 onion service descriptors (client mode or operating an onion service).
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 data0.3.5.150.4.4.90.4.5.9
Upgrade Tor clients and onion service operators to version 0.4.6.5 or later to patch the descriptor parsing vulnerability. Network operators may also consider filtering untrusted onion service descriptors at network boundaries.
- Consultation3.0 h
- Implementation6.0 h
- Testing5.0 h
- Review / QA3.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-34550 — 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-2021-34550 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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