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Fencer Vulns
medium 6.1

CVE-2021-39246 json

Tor Browser through 10.5.6 and 11.x through 11.0a4 allows a correlation attack that can compromise the privacy of visits to v2 onion addres…

published 2021-09-24 5 y ago modified 2026-06-17 4 mo ago also EUVD-2021-25608

cvss
6.1
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 41%
public exploits
0
none known

Summary

Tor Browser through 10.5.6 and 11.x through 11.0a4 allows a correlation attack that can compromise the privacy of visits to v2 onion addresses. Exact timestamps of these onion-service visits are logged locally, and an attacker might be able to compare them to timestamp data collected by the destination server (or collected by a rogue site within the Tor network).

Patch / fix

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-39246 updated cvss 4.7

tor: allows a correlation attack excessive verbose logging

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

0.47% chance of exploitation in the next 30 days, higher than 41% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • github.com https://github.com/sickcodes/security/blob/master/advisories/SICK-2021-111.md referenced PoC, tagged "exploit" by a source, unverified
  • sick.codes https://sick.codes/sick-2021-111 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 6.1 CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
NVD 2.0 3.6 AV:L/AC:L/Au:N/C:P/I:P/A:N

Classification

Weakness
  • CWE-532 Insertion of Sensitive Information into Log File

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.