CVE-2021-20247

Name: CVE-2021-20247
Creator: NVD / NIST
Published: 2021-02-23T19:15:13.51+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.4/10EPSS 1.88%

Last modified Jun 17, 2026

CVE-2021-20247 is a high-severity vulnerability rated 7.4/10 on the CVSS scale. A flaw was found in mbsync before v1.3.5 and v1.4.1. Validations of the mailbox names returned by IMAP LIST/LSUB do not occur allowing a malicious or compromised server to use specially crafted mailbox names containing '..' path components to access data outside the designated mailbox on the opposite end of the synchronization channel. EPSS estimates a 1.88% chance of exploitation in the next 30 days.

Description

A flaw was found in mbsync before v1.3.5 and v1.4.1. Validations of the mailbox names returned by IMAP LIST/LSUB do not occur allowing a malicious or compromised server to use specially crafted mailbox names containing '..' path components to access data outside the designated mailbox on the opposite end of the synchronization channel. The highest threat from this vulnerability is to data confidentiality and integrity.

Metrics

CVSS 3.1

7.4/10

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

EPSS Probability

1.88%

76.8th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Mbsync Project	Mbsync	< 1.3.5
Mbsync Project	Mbsync	>= 1.4.0, < 1.4.1
Fedoraproject	Extra Packages For Enterprise Linux	8.0
Debian	Debian Linux	9.0
Fedoraproject	Fedora	32
Fedoraproject	Fedora	33

References

https://bugzilla.redhat.com/show_bug.cgi?id=1928963Issue Tracking, Third Party Advisory
https://lists.debian.org/debian-lts-announce/2022/07/msg00001.htmlMailing List, Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/CAXQLCK35QGRCRENRTGKJO4VVZGUXUJJ/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/GVDEBZQJMWDW5JFK4NTHH6DAFNAZTESW/
https://security.gentoo.org/glsa/202208-15Third Party Advisory
https://www.openwall.com/lists/oss-security/2021/02/22/1Exploit, Mailing List, Third Party Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=1928963Issue Tracking, Third Party Advisory
https://lists.debian.org/debian-lts-announce/2022/07/msg00001.htmlMailing List, Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/CAXQLCK35QGRCRENRTGKJO4VVZGUXUJJ/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/GVDEBZQJMWDW5JFK4NTHH6DAFNAZTESW/
https://security.gentoo.org/glsa/202208-15Third Party Advisory
https://www.openwall.com/lists/oss-security/2021/02/22/1Exploit, Mailing List, Third Party Advisory

Timeline

Published: Feb 23, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-20247?

How severe is CVE-2021-20247?

CVE-2021-20247 has a CVSS score of 7.4/10 (HIGH severity). The EPSS model estimates a 1.88% probability of exploitation in the next 30 days.

How do I fix CVE-2021-20247?

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-2021-20247?

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

Scan your code now

Source: NVD / NIST