FedoraOperating system · Fedoraproject
CVE-2021-28090
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 attacker to cause Tor directory authorities to exit with an assertion failure, aka TROVE-2021-002.
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 remote attacker can send specially crafted network traffic to Tor directory authorities, triggering an assertion failure that causes these critical servers to exit unexpectedly. This constitutes a denial of service against the Tor network's infrastructure, as directory authorities are essential for client relay discovery and consensus information.
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
- Low
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
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 is installed on the systemCheck for the Tor package via system package manager (e.g., `rpm -q tor` on Fedora/RHEL, `dpkg -l tor` on Debian) or check for the tor binary at /usr/bin/torAffected if Tor is not installed or the package is not found
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Check the installed Tor versionRun `tor --version` or check the package version via package manager (e.g., `rpm -q tor` on Fedora)Affected if The version matches any of these ranges: < 0.3.5.14; 0.4.4.0 through 0.4.4.7; 0.4.5.0 through 0.4.5.6
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Determine if this Tor instance is configured as a directory authorityExamine the Tor configuration file (typically /etc/tor/torrc) for 'DirAuthority' directives, which designate the server as a directory authorityAffected if The configuration contains DirAuthority entries, indicating this is a directory authority
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Check the operating system version (if running Fedora 33)Run `cat /etc/fedora-release` or `rpm -q fedora-release` to confirm the Fedora versionAffected if The system is Fedora 33 with a vulnerable Tor version installed
You are affected only if this system runs Tor as a directory authority AND the installed Tor version falls within the affected ranges listed above.
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 all Tor directory authorities to version 0.4.5.7 or later. Consider implementing network-level rate limiting or filtering for anomalous traffic to directory authority ports as an interim measure.
Fix this in Fedora
Scoped from the published advisory
- Consultation2.0 h
- Implementation4.0 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 $3,088.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-28090 — 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-2021-28090 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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