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Vulnerability · Published Feb 23, 2021 · Assigned by redhat

CVE-2021-20247

High 7.4

In plain English

A high-severity improper input validation in isync/mbsync. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 1.9% (higher than 80% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS NVD)7.4High
Exploit odds (30 days)1.9%top 20.5% of all CVEs
Exploited in the wildNo reportsnot in CISA KEV
Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Alpine:v3.20isync1.4.1-r0ALPINE-CVE-2021-20247
Alpine:v3.21isync1.4.1-r0ALPINE-CVE-2021-20247
Alpine:v3.22isync1.4.1-r0ALPINE-CVE-2021-20247
Alpine:v3.23isync1.4.1-r0ALPINE-CVE-2021-20247
Alpine:v3.24isync1.4.1-r0ALPINE-CVE-2021-20247
Debian:12isync1.3.0-2.1DEBIAN-CVE-2021-20247
Debian:13isync1.3.0-2.1DEBIAN-CVE-2021-20247
Debian:14isync1.3.0-2.1DEBIAN-CVE-2021-20247
Ubuntu:22.04:LTSisyncno fix listedUBUNTU-CVE-2021-20247
Ubuntu:24.04:LTSisyncno fix listedUBUNTU-CVE-2021-20247
Ubuntu:25.10isyncno fix listedUBUNTU-CVE-2021-20247
Ubuntu:26.04:LTSisyncno fix listedUBUNTU-CVE-2021-20247
Ubuntu:26.10isyncno fix listedUBUNTU-CVE-2021-20247

Affected products (as reported)

VendorProductVersions
n/a isync/mbsync before 1.35before 1.4.1

Weakness: CWE-20

References