# CVE-2021-3578: Memory corruption in isync

> A malicious IMAP server can trigger a heap overflow in mbsync via a crafted APPENDUID response, potentially leading to remote code execution on the client.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/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:** 16 Feb 2022
- **Updated:** 3 Aug 2024
- **Also known as:** DEBIAN-CVE-2021-3578, GHSA-4r75-vj28-w5c7, UBUNTU-CVE-2021-3578, openSUSE-SU-2021:1170-1, openSUSE-SU-2021:1185-1

## What is CVE-2021-3578?

CVE-2021-3578 is a high-severity memory corruption vulnerability in Debian Debian Linux, published on 16 Feb 2022. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A flaw was found in mbsync before v1.3.6 and v1.4.2, where an unchecked pointer cast allows a malicious or compromised server to write an arbitrary integer value past the end of a heap-allocated structure by issuing an unexpected APPENDUID response. This could be plausibly exploited for remote code execution on the client.

Weakness: CWE-704 (Incorrect Type Conversion or Cast)

## Which versions are affected by CVE-2021-3578?

It affects 3 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `isync` | SUSE:Package Hub 15 SP2 | All versions | 1.3.6-bp152.4.6.1 |
| `isync` | openSUSE:Leap 15.2 | All versions | 1.3.6-lp152.4.6.1 |

Products: Debian Debian Linux, Fedoraproject Fedora, Isync Project Isync.

## How do I fix CVE-2021-3578?

Upgrade to a fixed version.

## Is CVE-2021-3578 being exploited?

There is no known exploitation of CVE-2021-3578 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-2021-3578 and fix it if it is affected.

What it is: CVE-2021-3578 is a high-severity memory corruption vulnerability in Debian Debian Linux, published on 16 Feb 2022. 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-2021-3578 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-2021-3578/ (Markdown: https://insights.sbomify.com/CVE-2021-3578/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3578
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3578
- OSV: https://osv.dev/vulnerability/CVE-2021-3578

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-3578/
Summaries are generated and may contain mistakes; the official description above is the record.