# CVE-2021-27241: Path traversal in Premium Security

> Local attackers can delete arbitrary directories via directory junctions in Avast Premium Security, causing denial of service.

- **Severity:** Medium 6.1 (`CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/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:** No
- **Published:** 29 Mar 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-76qj-3c6g-8v48

## What is CVE-2021-27241?

CVE-2021-27241 is a medium-severity path traversal vulnerability in Avast Premium Security, published on 29 Mar 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

This vulnerability allows local attackers to delete arbitrary directories on affected installations of Avast Premium Security 20.8.2429 (Build 20.8.5653.561). An attacker must first obtain the ability to execute low-privileged code on the target system in order to exploit this vulnerability. The specific flaw exists within the AvastSvc.exe module. By creating a directory junction, an attacker can abuse the service to delete a directory. An attacker can leverage this vulnerability to create a denial-of-service condition on the system. Was ZDI-CAN-12082.

Weakness: CWE-59 (Improper Link Resolution Before File Access)

## Which versions are affected by CVE-2021-27241?

It affects 1 product.


Products: Avast Premium Security.

## How do I fix CVE-2021-27241?

No fix has been published for CVE-2021-27241 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-27241 being exploited?

There is no known exploitation of CVE-2021-27241 in the wild and no public exploit code.

## Other vulnerabilities in Avast Premium Security

- [CVE-2023-42125](https://insights.sbomify.com/CVE-2023-42125/): Avast Premium Security Sandbox Protection Link Following Privilege Escalation Vulnerability (high 7.8)
- [CVE-2019-18894](https://insights.sbomify.com/CVE-2019-18894/): Command injection in n/a (high 7.8)
- [CVE-2022-28964](https://insights.sbomify.com/CVE-2022-28964/): Path traversal in n/a (high 7.1)
- [CVE-2022-28965](https://insights.sbomify.com/CVE-2022-28965/): Other in n/a (medium 6.5)
- [CVE-2023-42124](https://insights.sbomify.com/CVE-2023-42124/): Avast Premium Security Sandbox Protection Incorrect Authorization Privilege Escalation Vulnerability (medium 5.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-27241 and fix it if it is affected.

What it is: CVE-2021-27241 is a medium-severity path traversal vulnerability in Avast Premium Security, published on 29 Mar 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-2021-27241 in the wild and no public exploit code.

Affected product: Avast Premium Security. 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-2021-27241/ (Markdown: https://insights.sbomify.com/CVE-2021-27241/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-27241
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-27241
- OSV: https://osv.dev/vulnerability/CVE-2021-27241

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-27241/
Summaries are generated and may contain mistakes; the official description above is the record.