CVE-2026-77638

No known exploitation. EPSS puts it in the 20th percentile. A vendor fix is available.

CVSS 3.18.9High EPSS percentile20th0.3% chance in 30 days CISA KEVNot listedNo confirmed exploitation
No public exploit known FixVendor fixNo build named by the sources

Published 2026-08-20Updated 2026-09-16Sources: CVE.org, NVD

NVD CVE.org

What to do

The vendor has published a fix. Version details are below where the sources state them.

Steps

Written by AI from the record

Check the Tor version on every system that accesses or hosts onion services.
If it is earlier than 0.4.9.11, plan an upgrade through your operating system or Tor supplier.
Upgrade Tor to 0.4.9.11 or later.
After updating, test that your onion-service connections still work as expected.

Vendor advisory Usually a quick update

Check it yourselfA free OpenVAS check exists for this CVE. Run it against your hosts.Is your organisation exposed?Request an assessment to establish which checks fit your systems.

What it is

From the CVE record

Tor before 0.4.9.11 is prone to a race condition where in just the right circumstances a rendezvous point could man-in-the-middle (impersonate) the onion service that the client was trying to reach.

In plain language

Written by AI from the record

Tor versions before 0.4.9.11 can let a malicious relay impersonate an onion service during a rare connection timing issue, so small businesses using onion services should update.

A network-reachable CWE-362 race condition during Tor rendezvous establishment lets an attacker controlling the rendezvous point perform a man-in-the-middle impersonation of the target onion service.

If you're affected

Impersonated onion services
Altered communications
Sensitive data exposure
Fraudulent service responses

What is it

Tor can use a temporary meeting point to connect a visitor with an onion service. In rare circumstances, a dishonest meeting point can pose as the intended service—like an impostor answering the door of a business your staff meant to visit—and read or alter what passes through it.

Who is affected

This matters to you if your business uses Tor to access or run onion services. It is a risk only when an attacker controls the relay used as the connection’s meeting point and wins a narrow timing race during setup.

How urgent is it

An attacker would need to operate the connection’s meeting relay and exploit a precise timing window, which makes this an amber-priority update rather than an active emergency. There is no record of known public exploit code or confirmed real-world exploitation, but the possible interception and impersonation warrant scheduling the update promptly.

What to do — in detail

Confirm exposure by identifying Tor installations used by systems that access or host onion services, then check each installed version with the platform’s package inventory or tor --version.

Upgrade affected installations to 0.4.9.11 or later. The findings provide one fixed release and do not identify separate maintenance branches or upgrade-breaking changes; use the normal upgrade method for the operating system or Tor distribution in use.

No vendor-documented temporary workaround is provided in the findings. If an upgrade must be delayed, avoid using affected systems for sensitive onion-service activity where practical, and prioritize systems handling credentials, payments, or confidential business communications.

CISA has not added this CVE to its Known Exploited Vulnerabilities catalog, so there is no CISA remediation due date. Track Tor Project release notices and investigate unexpected identity, certificate, or content changes when connecting to important onion services.

Technical context

CVSS 3.1 score: 8.9 High (AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:L). The issue is CWE-362, a race condition in rendezvous establishment: a malicious rendezvous point can impersonate the onion service and man-in-the-middle the connection. Exploitation requires control of a rendezvous point plus specific timing. EPSS is 0.2% (9th percentile) and flat. The CVE is not in CISA KEV, and no public exploit code is on record; exploit maturity is therefore not publicly established.

This is a general assessment based on public vulnerability data. It does not account for your specific infrastructure — when in doubt, consult a security specialist.

Exploitation

Where each signal puts this CVE on the scale from published to confirmed exploited.

EPSS20th

CISA KEV

Not in the catalog. CISA has not confirmed exploitation.

Public exploits

No public exploit or proof of concept found in the sources we track.

EPSS

0.3% chance of exploitation activity in the next 30 days, which ranks it in the 20th percentile of scored CVEs.

Exploit Prediction Scoring System, FIRST.org. A probability, not a confirmation.

Lifecycle

9 events over 78 days, from the signal feeds we watch.

2026-09-16Patch availablerecord updated
2026-09-03Record updated
2026-08-27Record updated
2026-08-20Publishedweakness classified, att&ck mapped, record updated
2026-06-30OpenVAS check added

Affected products

torprojectoss-project · USaka tor
- TorMixedSecurity Products / secure-gateway-vpn

And 1 more affected product. See all after sign-in

Technical detail

CVSS 3.1 vector

Open in the CVSS calculator

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:L

Scored 8.9 by NVD.

How it is reached

Attack Vector NetworkExploitable remotely over the network without any special conditions
Attack Complexity HighRequires specific conditions like a race condition or non-default configuration
Privileges Required NoneNo authentication required — anyone can exploit this
User Interaction NoneNo user interaction needed — fully automated exploitation

Scope

Scope ChangedThe exploit can affect other components (e.g. sandbox escape, host compromise from VM)

Impact if exploited

Confidentiality HighTotal information disclosure — all data in the component is compromised
Integrity HighTotal loss of integrity — attacker can modify any data in the component
Availability LowReduced performance or intermittent disruption of service