# CVE-2021-20247: Path traversal in isync/mbsync

> A malicious IMAP server can exploit path traversal in mbsync to access or modify files outside the designated mailbox directory.

- **Severity:** High 7.4 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 23 Feb 2021
- **Updated:** 3 Aug 2024
- **Also known as:** DEBIAN-CVE-2021-20247, GHSA-5cp5-w68m-9w38, UBUNTU-CVE-2021-20247, openSUSE-SU-2021:0516-1, openSUSE-SU-2021:0533-1

## What is CVE-2021-20247?

CVE-2021-20247 is a high-severity path traversal vulnerability in Debian Debian Linux, published on 23 Feb 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A flaw was found in mbsync before v1.3.5 and v1.4.1. Validations of the mailbox names returned by IMAP LIST/LSUB do not occur allowing a malicious or compromised server to use specially crafted mailbox names containing '..' path components to access data outside the designated mailbox on the opposite end of the synchronization channel. The highest threat from this vulnerability is to data confidentiality and integrity.

Weakness: CWE-22 (Improper Limitation of a Pathname to a Restricted Directory), CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2021-20247?

It affects 4 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `isync` | SUSE:Package Hub 15 SP2 | All versions | 1.3.5-bp152.4.3.1 |
| `isync` | openSUSE:Leap 15.2 | All versions | 1.3.5-lp152.4.3.1 |

Products: Debian Debian Linux, Fedoraproject Extra Packages for Enterprise Linux, Fedoraproject Fedora, Mbsync Project Mbsync.

## How do I fix CVE-2021-20247?

Upgrade to a fixed version.

## Is CVE-2021-20247 being exploited?

There is no known exploitation of CVE-2021-20247 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

- [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild)
- [CVE-2025-49113](https://insights.sbomify.com/CVE-2025-49113/): RoundCube Webmail Deserialization of Untrusted Data (critical 9.9, exploited in the wild)
- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild)
- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-20247 and fix it if it is affected.

What it is: CVE-2021-20247 is a high-severity path traversal vulnerability in Debian Debian Linux, published on 23 Feb 2021. 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-2021-20247 in the wild and no public exploit code.

Affected product: Debian Debian Linux. 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-2021-20247/ (Markdown: https://insights.sbomify.com/CVE-2021-20247/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-20247
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-20247
- OSV: https://osv.dev/vulnerability/CVE-2021-20247

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-20247/
Summaries are generated and may contain mistakes; the official description above is the record.