# CVE-2020-23856: Use after free in n/a

> A use-after-free flaw in GNU cflow allows attackers to cause a denial of service via a crafted input file.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 18 May 2021
- **Updated:** 4 Aug 2024
- **Also known as:** DEBIAN-CVE-2020-23856, GHSA-h5qf-rf3c-vmj5, UBUNTU-CVE-2020-23856

## What is CVE-2020-23856?

CVE-2020-23856 is a medium-severity use after free vulnerability in Fedoraproject Fedora, published on 18 May 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Use-after-Free vulnerability in cflow 1.6 in the void call(char *name, int line) function at src/parser.c, which could cause a denial of service via the pointer variable caller->callee.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2020-23856?

It affects 2 products.


Products: Fedoraproject Fedora, Gnu Cflow.

## How do I fix CVE-2020-23856?

Apply the vendor's patch.

## Is CVE-2020-23856 being exploited?

There is no known exploitation of CVE-2020-23856 in the wild and no public exploit code.

## Other vulnerabilities in Fedoraproject Fedora

- [CVE-2024-4577](https://insights.sbomify.com/CVE-2024-4577/): PHP-CGI OS Command Injection (critical 9.8, exploited in the wild)
- [CVE-2021-39226](https://insights.sbomify.com/CVE-2021-39226/): Grafana Authentication Bypass (critical 9.8, exploited in the wild)
- [CVE-2019-5544](https://insights.sbomify.com/CVE-2019-5544/): VMware ESXi and Horizon DaaS OpenSLP Heap-Based Buffer Overflow (critical 9.8, exploited in the wild)
- [CVE-2024-4947](https://insights.sbomify.com/CVE-2024-4947/): Google Chromium V8 Type Confusion (critical 9.6, exploited in the wild)
- [CVE-2024-4671](https://insights.sbomify.com/CVE-2024-4671/): Google Chromium Visuals Use-After-Free (critical 9.6, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-23856 and fix it if it is affected.

What it is: CVE-2020-23856 is a medium-severity use after free vulnerability in Fedoraproject Fedora, published on 18 May 2021. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2020-23856 in the wild and no public exploit code.

Affected product: Fedoraproject Fedora. 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-2020-23856/ (Markdown: https://insights.sbomify.com/CVE-2020-23856/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-23856
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-23856
- OSV: https://osv.dev/vulnerability/CVE-2020-23856

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-23856/
Summaries are generated and may contain mistakes; the official description above is the record.