Debian LinuxOperating system · Debian
CVE-2017-8820
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 · uneditedIn Tor before 0.2.5.16, 0.2.6 through 0.2.8 before 0.2.8.17, 0.2.9 before 0.2.9.14, 0.3.0 before 0.3.0.13, and 0.3.1 before 0.3.1.9, remote attackers can cause a denial of service (NULL pointer dereference and application crash) against directory authorities via a malformed descriptor, aka TROVE-2017-010.
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 NULL pointer dereference vulnerability in Tor allows remote attackers to crash directory authorities by sending malformed descriptors, causing denial of service. The vulnerability affects multiple version branches of Tor prior to patched releases.
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
= 8.0= 9.0< 0.2.5.16>= 0.2.6, < 0.2.8.17>= 0.2.9, < 0.2.9.14>= 0.3.0, < 0.3.0.13>= 0.3.1, < 0.3.1.9CVSS 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:3.0/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 if Tor is installedRun 'dpkg -l | grep tor' on Debian-based systems to list installed Tor packages, or check for the tor binary with 'which tor'Affected if No Tor package is found - the system is not running Tor and is not affected
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Identify installed Tor versionRun 'tor --version' or 'dpkg -l | grep tor' to see the exact version number of the installed Tor packageAffected if The installed version falls within one of these ranges: < 0.2.5.16, >= 0.2.6 and < 0.2.8.17, >= 0.2.9 and < 0.2.9.14, >= 0.3.0 and < 0.3.0.13, or >= 0.3.1 and < 0.3.1.9
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Determine if Tor is configured as a directory authorityInspect the Tor configuration file (typically /etc/tor/torrc) and look for 'DirAuthority' directives, or check for the presence of 'authoritative directory' related configurationAffected if The Tor configuration contains DirAuthority entries or is explicitly configured as a directory authority - this is required for the vulnerability to be exploitable
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Verify Tor service statusRun 'systemctl status tor' or check if the Tor process is running with 'ps aux | grep tor'Affected if Tor is not running - no active attack surface exists even with vulnerable version
The system is affected only if it runs a vulnerable Tor version (in the affected ranges) AND is configured as a directory authority with DirAuthority settings in torrc.
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 data0.2.5.160.2.8.170.2.9.14
Upgrade Tor installations to version 0.2.5.16, 0.2.8.17, 0.2.9.14, 0.3.0.13, or 0.3.1.9 or later to remediate this vulnerability.
Fix this in Debian Linux
Scoped from the published advisory
- Consultation3.0 h
- Implementation6.0 h
- Testing3.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,984.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2017-8820 — 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-2017-8820 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
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