CVE-2021-3578: Debian Linux

High severity, CVSS 7.8. EPSS: 1% chance of exploitation in the next 30 days.

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.

Affected products

• Debian Debian Linux: version 9.0 only
• Fedoraproject Fedora: version 33 only; version 34 only
• Isync Project Isync: before 1.3.6 (fixed in 1.3.6); version 1.4.0 only; version 1.4.1 only

Published 2022-02-16. Last modified 2026-06-17.