---
id: CVE-2026-77641
title: "tor before 0.4.9.9 was prone to a\_NULL write after free when sending a CONFLUX_SWITCH cell fails"
summary: "tor before 0.4.9.9 was prone to a\_NULL write after free when sending a CONFLUX_SWITCH cell fails. The return value of relay_send_command_from_edge() was   ignored, so a send failure (which calls circuit_mark_for_close()  and removes the …"
severity: medium
cvss: 6.5
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H'
cwe:
  - CWE-252
vendor: torproject
product: tor
affected:
  - tor < 0.4.9.9
patched:
  - tor 0.4.9.9
published: '2026-08-20'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T18:23:16.410'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-77641'
references:
  - url: 'https://gitlab.torproject.org/tpo/core/tor/-/raw/tor-0.4.9.9/ChangeLog'
    label: cve@mitre.org
tags:
  - nvd
epss: 0.00202
epssPercentile: 0.10413
ingestedAt: '2026-09-08T19:08:49.591Z'
---

## Overview

tor before 0.4.9.9 was prone to a NULL write after free when sending a CONFLUX_SWITCH cell fails. The return value of relay_send_command_from_edge() was   ignored, so a send failure (which calls circuit_mark_for_close()  and removes the leg via cfx_del_leg()) would go undetected, causing the caller to write to the now-freed current leg and resulting in a crash. This is TROVE-2026-017.

## Affected

- `tor < 0.4.9.9`

## Remediation

Upgrade past the affected range:

- `tor 0.4.9.9`