CVE-2021-3657

Name: CVE-2021-3657
Creator: NVD / NIST
Published: 2022-02-18T18:15:09.603+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.8/10EPSS 3.27%

Last modified Jun 17, 2026

CVE-2021-3657 is a critical-severity vulnerability rated 9.8/10 on the CVSS scale. 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.. EPSS estimates a 3.27% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

9.8/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Probability

3.27%

86.8th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Isync Project	Isync	< 1.4.4
Fedoraproject	Fedora	35
Redhat	Enterprise Linux	7.0
Debian	Debian Linux	9.0

References

https://bugzilla.redhat.com/show_bug.cgi?id=2028932Issue Tracking, Third Party Advisory
https://lists.debian.org/debian-lts-announce/2022/07/msg00001.htmlMailing List, Third Party Advisory
https://security.gentoo.org/glsa/202208-15Third Party Advisory
https://www.openwall.com/lists/oss-security/2021/12/03/1Mailing List, Third Party Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=2028932Issue Tracking, Third Party Advisory
https://lists.debian.org/debian-lts-announce/2022/07/msg00001.htmlMailing List, Third Party Advisory
https://security.gentoo.org/glsa/202208-15Third Party Advisory
https://www.openwall.com/lists/oss-security/2021/12/03/1Mailing List, Third Party Advisory

Timeline

Published: Feb 18, 2022
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-3657?

How severe is CVE-2021-3657?

CVE-2021-3657 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 3.27% probability of exploitation in the next 30 days.

How do I fix CVE-2021-3657?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-3657?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST