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CVE-2026-77639

MEDIUM
5.3
CVSS Score
Published: August 20, 2026 at 08:57 PM UTC
Updated: October 18, 2026 at 08:10 PM UTC
1 product affected across 1 vendorTor

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Severity
MEDIUM5.3
Exploit prediction
EPSS 0.4%
SSVC
No known exploit

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Tor· Torproject
95%
v < 0.4.9.90.3.1.1-alpha
Affected range stops below 0.4.9.9, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

References (1)

Release NotesVendor Advisory
Source: cverecord
https://gitlab.torproject.org/tpo/core/tor/-/raw/tor-0.4.9.9/ChangeLog

SSVC — Action Prioritization

SSVCNo known exploitAutomatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

5.3MEDIUMmitre
Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
NONE
Availability
LOW
Vector?

Quick Info

StatusANALYZED
CWE
CWE-420

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