FedoraOperating system · Fedoraproject
CVE-2021-28089
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 0.4.5.7 allows a remote participant in the Tor directory protocol to exhaust CPU resources on a target, aka TROVE-2021-001.
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 version 0.4.5.7 contains a denial-of-service vulnerability in its directory protocol. A remote attacker participating in the Tor directory protocol can send specially crafted messages that cause excessive CPU consumption on target Tor nodes, potentially degrading network performance or causing service unavailability.
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
FedoraOperating system
= 33< 0.3.5.14>= 0.4.4.4, < 0.4.4.8>= 0.4.5.0, < 0.4.5.7= 0.4.4.0= 0.4.4.1= 0.4.4.2= 0.4.4.3CVSS 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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Identify installed Tor versionRun 'tor --version' or check the package manager (e.g., 'rpm -q tor' on RHEL/Fedora, 'dpkg -l tor' on Debian). On Windows, check Tor's properties or use 'tor --version' if installed with expert bundle.Affected if The installed version is earlier than 0.3.5.14, or falls between 0.4.4.0 and 0.4.4.7 inclusive, or between 0.4.5.0 and 0.4.5.6 inclusive.
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Confirm Tor is running as a relay or bridgeInspect the torrc configuration file (typically at /etc/tor/torrc or /usr/local/etc/tor/torrc) and look for 'ORPort' or 'Bridge' directives. Alternatively, query the Tor control port using 'echo -e 'PROTOCOLINFO QUIT ' | nc localhost 9051' to check relay status.Affected if The node is configured as a relay (with ORPort set) or a bridge. Client-only installations are less directly affected since the vulnerability is in the directory protocol handling on the receiving node.
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Verify directory protocol exposureCheck if the node is configured as a directory authority or mirror. Look for 'DirPort' in the torrc configuration. Also verify network listen addresses include ports commonly used for directory protocol (ports 80, 443, or custom DirPort).Affected if DirPort is enabled and reachable from the network, meaning the node accepts directory protocol connections from other Tor participants.
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Check Fedora version if applicableIf running on Fedora 33, run 'cat /etc/fedora-release' or 'fedora-release' package query to confirm the distribution version.Affected if Running Fedora 33 with a vulnerable Tor package version installed.
You are affected if your Tor version is earlier than 0.4.5.7 (or in the other vulnerable ranges) AND your node is configured as a relay, bridge, or directory mirror that accepts directory protocol connections from the network.
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 data0.3.5.140.4.4.80.4.5.7
Upgrade Tor installations to version 0.4.5.7 or later. For systems that cannot be immediately upgraded, consider rate-limiting or filtering directory protocol connections from untrusted sources at the network perimeter.
Fix this in Fedora
Scoped from the published advisory
- Consultation2.0 h
- Implementation4.0 h
- Testing4.0 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 $3,328.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-28089 — 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-2021-28089 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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