CVE-2026-77641Network attack vectorHinoki check available

Crash via ignored CONFLUX_SWITCH send failure

Published Aug 20, 2026 · Updated Aug 20, 2026

Use-after-free in Conflux circuit handling in The Tor Project Tor before 0.4.9.9 allows remote attackers to crash Tor via a failed CONFLUX_SWITCH send. After relay_send_command_from_edge() reports a send failure, the caller ignores that return value even though the failure path closes the circuit and removes the current leg through cfx_del_leg(), then continues and writes through the freed leg pointer. Exposure requires reachability to the Conflux code path and the ability to trigger that send failure; published records describe process crash and memory-corruption side effects, but not code execution.

CVSS severity6.5
Medium
EPSS probability0.20%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

Use-after-free in Conflux circuit handling in The Tor Project Tor before 0.4.9.9 allows remote attackers to crash Tor via a failed CONFLUX_SWITCH send. After relay_send_command_from_edge() reports a send failure, the caller ignores that return value even though the failure path closes the circuit and removes the current leg through cfx_del_leg(), then continues and writes through the freed leg pointer. Exposure requires reachability to the Conflux code path and the ability to trigger that send failure; published records describe process crash and memory-corruption side effects, but not code execution.

The record

CVE
CVE-2026-77641
Published
Aug 20, 2026
Updated
Aug 20, 2026
Vendor
The Tor Project
Product
Tor
Classifications
CWE-252, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 20, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 20, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0.4.8.1-alpha <0.4.9.9

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Tor Project · Torversion=0.4.8.1-alpha <0.4.9.9

Published CVSS scores

6.5MITRECVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-252Unchecked Return Value
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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