# CVE-2026-77641: Use after free in Tor

> A use-after-free vulnerability in Tor allows remote attackers to cause a denial of service via a failed CONFLUX_SWITCH cell transmission.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 20 Aug 2026
- **Updated:** 27 Aug 2026
- **Also known as:** DEBIAN-CVE-2026-77641, GHSA-r3c6-fj5w-6f75, UBUNTU-CVE-2026-77641

## What is CVE-2026-77641?

CVE-2026-77641 is a medium-severity use after free vulnerability in torproject Tor, published on 20 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-252 (Unchecked Return Value)

## Which versions are affected by CVE-2026-77641?

It affects 1 product.


Products: Torproject Tor.

## How do I fix CVE-2026-77641?

Upgrade to a fixed version.

## Is CVE-2026-77641 being exploited?

There is no known exploitation of CVE-2026-77641 in the wild and no public exploit code.

## Other vulnerabilities in torproject Tor

- [CVE-2026-77638](https://insights.sbomify.com/CVE-2026-77638/): Race condition in Tor (high 8.9)
- [CVE-2026-77642](https://insights.sbomify.com/CVE-2026-77642/): Memory corruption in Tor (high 7.5)
- [CVE-2022-33903](https://insights.sbomify.com/CVE-2022-33903/): Denial of service in n/a (high 7.5)
- [CVE-2021-38385](https://insights.sbomify.com/CVE-2021-38385/): Denial of service in n/a (high 7.5)
- [CVE-2021-34548](https://insights.sbomify.com/CVE-2021-34548/): Security feature bypass in n/a (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-77641 and fix it if it is affected.

What it is: CVE-2026-77641 is a medium-severity use after free vulnerability in torproject Tor, published on 20 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-77641 in the wild and no public exploit code.

Affected product: torproject Tor. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-77641/ (Markdown: https://insights.sbomify.com/CVE-2026-77641/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-77641
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-77641
- OSV: https://osv.dev/vulnerability/CVE-2026-77641

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-77641/
Summaries are generated and may contain mistakes; the official description above is the record.