CVE-2021-44143
📋 TL;DR
A heap overflow vulnerability in mbsync component of isync allows remote code execution when processing malicious email messages from a compromised IMAP server. This affects users of isync versions 1.4.0 through 1.4.3 who synchronize email with untrusted or compromised IMAP servers. The vulnerability is triggered by specially crafted messages that lack proper headers.
💻 Affected Systems
- isync
- mbsync
📦 What is this software?
Fedora by Fedoraproject
Fedora by Fedoraproject
Isync by Isync Project
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution with the privileges of the mbsync process, potentially leading to full system compromise.
Likely Case
Application crash (denial of service) with potential for remote code execution if exploit is refined.
If Mitigated
No impact if patched version is used or if IMAP server is trusted and not compromised.
🎯 Exploit Status
Exploitation requires a malicious or compromised IMAP server to send crafted messages. Client must initiate synchronization.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.4.4 and later
Vendor Advisory: http://www.openwall.com/lists/oss-security/2021/12/03/2
Restart Required: Yes
Instructions:
1. Check current version: mbsync -V
2. Update via package manager: apt/yum/dnf update isync
3. Or compile from source: Download isync 1.4.4+ from https://isync.sourceforge.io/
4. Restart any mbsync processes or services.
🔧 Temporary Workarounds
Disable IMAP synchronization
allTemporarily disable mbsync IMAP synchronization until patched.
Comment out IMAP channels in ~/.mbsyncrc or rename config file
Use trusted IMAP servers only
allConfigure mbsync to only connect to trusted, internal IMAP servers.
Edit ~/.mbsyncrc to restrict IMAPHost to trusted servers
🧯 If You Can't Patch
- Run mbsync with reduced privileges using chroot or containerization
- Monitor mbsync processes for crashes or unusual behavior
🔍 How to Verify
Check if Vulnerable:
Run: mbsync -V | grep -E '1\.4\.[0-3]' - if output shows version 1.4.0-1.4.3, system is vulnerable.Check Version:
mbsync -VVerify Fix Applied:
Run: mbsync -V | grep -E '1\.4\.[4-9]|1\.[5-9]' - should show version 1.4.4 or higher.📡 Detection & Monitoring
Log Indicators:
- mbsync process crashes
- segmentation faults in system logs
- unusual memory usage patterns
Network Indicators:
- Unexpected connections from mbsync to unknown IMAP servers
- Large or malformed IMAP responses
SIEM Query:
process.name:"mbsync" AND (event.action:"segmentation_fault" OR event.outcome:"failure")🔗 References
- http://www.openwall.com/lists/oss-security/2021/12/03/2
- https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=999804
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/CYZ2GNB4ZO2T27D2XNUWMCS3THZYSJQU/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/LCBSY7OZ57XNC6ZYXF6WU5KBSWITZVDX/
- https://security.gentoo.org/glsa/202208-15
- https://sourceforge.net/p/isync/isync/commit_browser
- https://sourceforge.net/p/isync/isync/ref/master/tags/
- http://www.openwall.com/lists/oss-security/2021/12/03/2
- https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=999804
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/CYZ2GNB4ZO2T27D2XNUWMCS3THZYSJQU/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/LCBSY7OZ57XNC6ZYXF6WU5KBSWITZVDX/
- https://security.gentoo.org/glsa/202208-15
- https://sourceforge.net/p/isync/isync/commit_browser
- https://sourceforge.net/p/isync/isync/ref/master/tags/
