# CVE-2018-20535: Use after free in n/a

> A use-after-free vulnerability in Netwide Assembler allows attackers to cause a denial of service via crafted input.

- **Severity:** Medium 5.5 (`CVSS:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 28 Dec 2018
- **Updated:** 5 Aug 2024
- **Also known as:** DEBIAN-CVE-2018-20535, GHSA-rvm6-q4p6-g665, UBUNTU-CVE-2018-20535

## What is CVE-2018-20535?

CVE-2018-20535 is a medium-severity use after free vulnerability in Nasm Netwide Assembler, published on 28 Dec 2018. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

There is a use-after-free at asm/preproc.c (function pp_getline) in Netwide Assembler (NASM) 2.14rc16 that will cause a denial of service during a line-number increment attempt.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2018-20535?

It affects 1 product.


Products: Nasm Netwide Assembler.

## How do I fix CVE-2018-20535?

Upgrade to a fixed version.

## Is CVE-2018-20535 being exploited?

There is no known exploitation of CVE-2018-20535 in the wild and no public exploit code.

## Other vulnerabilities in Nasm Netwide Assembler

- [CVE-2004-1287](https://insights.sbomify.com/CVE-2004-1287/): Memory corruption in n/a (critical 10.0)
- [CVE-2020-24978](https://insights.sbomify.com/CVE-2020-24978/): Use after free in n/a (critical 9.8)
- [CVE-2008-7177](https://insights.sbomify.com/CVE-2008-7177/): Memory corruption in n/a (critical 9.3)
- [CVE-2023-31722](https://insights.sbomify.com/CVE-2023-31722/): Memory corruption in n/a (high 7.8)
- [CVE-2022-44370](https://insights.sbomify.com/CVE-2022-44370/): Memory corruption in n/a (high 7.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2018-20535 and fix it if it is affected.

What it is: CVE-2018-20535 is a medium-severity use after free vulnerability in Nasm Netwide Assembler, published on 28 Dec 2018. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2018-20535 in the wild and no public exploit code.

Affected product: Nasm Netwide Assembler. 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-2018-20535/ (Markdown: https://insights.sbomify.com/CVE-2018-20535/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2018-20535
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2018-20535
- OSV: https://osv.dev/vulnerability/CVE-2018-20535

---
From sbomify Insights: https://insights.sbomify.com/CVE-2018-20535/
Summaries are generated and may contain mistakes; the official description above is the record.