# CVE-2018-0491: Use after free in Tor

> Remote attackers can crash Tor relays via a use-after-free flaw in the KIST implementation, requiring an upgrade to mitigate.

- **Severity:** High 7.5 (`CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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:** 5 Mar 2018
- **Updated:** 5 Aug 2024
- **Also known as:** DEBIAN-CVE-2018-0491, GHSA-8wr4-7fjq-4qxw, UBUNTU-CVE-2018-0491

## What is CVE-2018-0491?

CVE-2018-0491 is a high-severity use after free vulnerability in Tor, published on 5 Mar 2018. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A use-after-free issue was discovered in Tor 0.3.2.x before 0.3.2.10. It allows remote attackers to cause a denial of service (relay crash) because the KIST implementation allows a channel to be added more than once in the pending list.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2018-0491?

It affects 1 product.


Products: Torproject Tor.

## How do I fix CVE-2018-0491?

Upgrade to a fixed version.

## Is CVE-2018-0491 being exploited?

There is no known exploitation of CVE-2018-0491 in the wild and no public exploit code.

Public exploit code:

- Tor Browser < 0.3.2.10 - Use After Free (PoC) (exploitdb)

## Other vulnerabilities in 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-2018-0491 and fix it if it is affected.

What it is: CVE-2018-0491 is a high-severity use after free vulnerability in Tor, published on 5 Mar 2018. 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-2018-0491 in the wild and no public exploit code.

Affected product: 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-2018-0491/ (Markdown: https://insights.sbomify.com/CVE-2018-0491/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2018-0491
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2018-0491
- OSV: https://osv.dev/vulnerability/CVE-2018-0491

---
From sbomify Insights: https://insights.sbomify.com/CVE-2018-0491/
Summaries are generated and may contain mistakes; the official description above is the record.