5.3

CVE-2026-77639: torproject tor Unprotected Alternate Channel

CVSS: 5.3v3.1MediumAnalyzed
AliasesUBUNTU-CVE-2026-77639DEBIAN-CVE-2026-77639
Published 20-08-2026Last modified 21-08-2026
Open JSON

Vulnerability summary

CVE-2026-77639 is a medium (CVSS 5.3) Unprotected Alternate Channel vulnerability in torproject tor. EPSS estimates a 0.39% chance of exploitation in the next 30 days, higher than 31.6% of scored vulnerabilities.

Overall risk
21/100
0100
Low · default modelHow is this calculated?
CVSS score
5.3/10
010
Medium · v3.1 (CVE.org)
EPSS score
0.39%
0%100%
Low · +0.16 pp in 30 days
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 1
MGASA-2026-0382

Timeline

  1. 20-08-2026
    PublishedVulnerability first disclosed.
  2. 21-08-2026
    Last modifiedVulnerability information updated.

Description

Tor before 0.4.9.9 was prone to a compression bomb bypass where an attacker could concatenate many gzip or zlib sub-streams, each just under the per-stream detection threshold, to avoid the compression bomb check entirely. This is TROVE-2026-022.

CVSS metrics

4 scores · 4 sources · 1 version

EPSS trend

Probability

0.39%

Chance of exploitation in the next 30 days

Percentile

32%

Versus all other CVEs

30-day change

+0.16 pp

From 0.23% on 19-09-2026

19-09-202619-10-2026
EPSS score
0.39%

Known exploited

Compare KEV catalogs

Not in any of the 3 tracked catalogs.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Debian1 product
  • tor< 0.4.9.9-1 | < 0.4.9.11-0+deb13u1
Torproject1 product
  • tor≥ 0.3.1.1-alpha, < 0.4.9.9 | < 0.4.9.9
Ubuntu1 product
  • torAll versions (No fix recorded)

3 vendors · 3 products

References

5 links