# CVE-2018-20821: Denial of service in n/a

> Attackers can cause a denial of service in LibSass via uncontrolled recursion during CSS variable value parsing.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/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:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 23 Apr 2019
- **Updated:** 5 Aug 2024
- **Also known as:** DEBIAN-CVE-2018-20821, GHSA-j7pw-5g39-c2cj, JLSEC-2026-504

## What is CVE-2018-20821?

CVE-2018-20821 is a medium-severity denial of service vulnerability in n/a, published on 23 Apr 2019. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

The parsing component in LibSass through 3.5.5 allows attackers to cause a denial-of-service (uncontrolled recursion in Sass::Parser::parse_css_variable_value in parser.cpp).

Weakness: CWE-674 (Uncontrolled Recursion)

## Which versions are affected by CVE-2018-20821?

It affects 1 product.


Products: Sass-Lang Libsass.

## How do I fix CVE-2018-20821?

Upgrade to a fixed version.

## Is CVE-2018-20821 being exploited?

There is no known exploitation of CVE-2018-20821 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2018-11499](https://insights.sbomify.com/CVE-2018-11499/): Use after free in n/a (critical 9.8)
- [CVE-2022-26592](https://insights.sbomify.com/CVE-2022-26592/): Memory corruption in n/a (high 8.8)
- [CVE-2018-19827](https://insights.sbomify.com/CVE-2018-19827/): Use after free in n/a (high 8.8)
- [CVE-2018-11694](https://insights.sbomify.com/CVE-2018-11694/): Null dereference in n/a (high 8.8)
- [CVE-2018-11695](https://insights.sbomify.com/CVE-2018-11695/): Null dereference in n/a (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2018-20821 and fix it if it is affected.

What it is: CVE-2018-20821 is a medium-severity denial of service vulnerability in n/a, published on 23 Apr 2019. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2018-20821 in the wild and no public exploit code.

Affected product: n/a. 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-2018-20821/ (Markdown: https://insights.sbomify.com/CVE-2018-20821/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2018-20821
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2018-20821
- OSV: https://osv.dev/vulnerability/CVE-2018-20821

---
From sbomify Insights: https://insights.sbomify.com/CVE-2018-20821/
Summaries are generated and may contain mistakes; the official description above is the record.