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CVE-2017-0377: Tor 0.3.x before 0.3.0.9 has a guard-selection algorithm that only considers the exit relay (not the exit r...

Tor 0.3.x before 0.3.0.9 has a guard-selection algorithm that only considers the exit relay (not the exit relay's family), which might allow remote attackers to defeat intended anonymity properties by leveraging the existence of large families.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This flaw could weaken Tor users' anonymity. Vulnerable Tor 0.3.x clients before 0.3.0.9 did not account for an exit relay's family during guard selection, creating a path for attackers with large relay families to erode intended anonymity protections.

Executive priority

Treat this as targeted privacy risk, not an infrastructure takeover issue. Prioritize remediation where Tor is used for sensitive investigations, source protection, whistleblowing, research, or any workflow where deanonymization would create material harm.

Technical view

CVE-2017-0377 affects Tor 0.3.x before 0.3.0.9. The guard-selection algorithm considered only the selected exit relay, not related relays in the exit relay family. The reported impact is potential defeat of anonymity properties, not code execution or service compromise.

Likely exposure

Exposure is most likely limited to legacy Tor 0.3.x installations older than 0.3.0.9, especially clients whose anonymity assumptions depend on guard selection. Current supported Tor packages are unlikely to be affected, but verify rather than assume.

Exploitation context

The provided sources do not show CISA KEV listing, public active exploitation, or exploit tooling. The CVE describes a remote anonymity weakness that depends on large relay families, so risk is most relevant to users relying on Tor for identity protection.

Researcher notes

Evidence identifies an algorithmic anonymity flaw in guard selection. Source data lacks CVSS, CWE, and KEV status. Analysis should stay focused on version exposure and release-tracker confirmation, without assuming broader Tor versions or unrelated anonymity attacks.

Mitigation direction

  • Upgrade Tor 0.3.x clients to 0.3.0.9 or a later vendor-supported fixed release.
  • Check Debian or other distribution security trackers for package-specific fixed versions.
  • Remove or isolate unsupported legacy Tor builds from sensitive workflows.
  • Review Tor Project release notes for client security update guidance.

Validation and detection

  • Inventory Tor client versions across endpoints, servers, and packaged appliances.
  • Confirm no Tor 0.3.x installation is older than 0.3.0.9.
  • Check distribution package metadata against Debian or vendor security tracker status.
  • Document any remaining legacy Tor use and its business owner.
Prepared
Confidence
medium
Sources
7

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

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CVE-2017-0377 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
0Timeline events
0ADP providers
6Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/aTorTorListed
Weakness

CWE details

No CWE listed

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.