5.3

CVE-2026-77640: torproject tor

CVSS: 5.3v3.1MediumAnalyzed
AliasesUBUNTU-CVE-2026-77640DEBIAN-CVE-2026-77640
Published 20-08-2026Last modified 21-08-2026
Open JSON

Vulnerability summary

CVE-2026-77640 is a medium (CVSS 5.3) vulnerability in torproject tor. EPSS estimates a 0.38% chance of exploitation in the next 30 days, higher than 30.2% of scored vulnerabilities.

Overall risk
21/100
0100
Low · default modelHow is this calculated?
CVSS score
5.3/10
010
Medium · v3.1 (NVD)
EPSS score
0.38%
0%100%
Low · +0.15 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 an infinite loop when decompressing a truncated zlib/gzip stream with done=1. A truncated stream never reaches Z_STREAM_END, causing zlib to return Z_BUF_ERROR with no input remaining, which buf_add_compress() mistook for a full output buffer and retried forever. Fixed by returning TOR_COMPRESS_ERROR in that case so the caller can abort cleanly. This is TROVE-2026-021.

CVSS metrics

4 scores · 4 sources · 1 version

EPSS trend

Probability

0.38%

Chance of exploitation in the next 30 days

Percentile

30%

Versus all other CVEs

30-day change

+0.15 pp

From 0.22% on 19-09-2026

19-09-202619-10-2026
EPSS score
0.38%

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≥ 0.2.6.1-alpha, < 0.4.9.9 | < 0.4.9.9
Ubuntu1 product
  • torAll versions (No fix recorded)

3 vendors · 3 products

References

5 links