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Vulnerability record · CVE-2021-3657 · published 18 February 2022

CVE-2021-3657: Isync project isync memory buffer overflow vulnerability

Isync Project · Isync

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.

9.8 CVSS 3.1 Critical EPSS 3.5% · top 11.1% CWE-119 · Memory buffer overflow
9.8CVSS 3.1 base score, v2 7.5
3.5%EPSS exploitation probability, 30 days
NoNot in CISA KEV
4Affected product versions listed by NVD
8References
17 Jun 2026Last modified by NVD

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.

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

Affected products

4 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

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

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Source: NIST National Vulnerability Database (record CVE-2021-3657), CISA KEV, FIRST EPSS (scores of 2026-10-14). This page is refreshed as NVD updates the record.