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CVE-2021-20247

A flaw was found in mbsync before v1.3.5 and v1.4.1. Validations of the mailbox names returned by...

7.4 HighFix available

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.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
High
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
High
Integrity
High
Availability
None

Exploit likelihood

1.88%Up 0.8 points since Apr 14, 2021
90%50%10%1%

What each source reports

NVD Score used 7.4

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.

Record
CVE-2021-20247
CVSS 3.1
7.4 HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
CVSS 2.0
5.8 MediumAV:N/AC:M/Au:N/C:P/I:P/A:N
Weakness
CWE-20, CWE-22
Updated
2026-11-02
CVE List No score

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.

Record
CVE-2021-20247
Weakness
CWE-20
Updated
2026-11-02
EUVDEUVD-2021-7686 No score

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.

Record
EUVD-2021-7686
Updated
2026-11-03
GitHub AdvisoriesGHSA-5cp5-w68m-9w38 7.4

A flaw was found in mbsync before v1.3.5 and v1.4.1. Validations of the mailbox names returned by...

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.

Record
GHSA-5cp5-w68m-9w38
CVSS 3.1
7.4 HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Weakness
CWE-20, CWE-22
Updated
2026-11-02
OSVALPINE-CVE-2021-20247 7.4

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.

Record
ALPINE-CVE-2021-20247
CVSS 3.1
7.4 HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Updated
2026-11-03
OSV 7.4

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.

Record
CVE-2021-20247
CVSS 3.1
7.4 HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Updated
2026-11-02
Show 5 moreShow less
OSVDEBIAN-CVE-2021-20247 7.4

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.

Record
DEBIAN-CVE-2021-20247
CVSS 3.1
7.4 HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Updated
2026-11-02
OSVUBUNTU-CVE-2021-20247 7.4

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.

Record
UBUNTU-CVE-2021-20247
CVSS 3.1
7.4 HighCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Updated
2026-11-02
OSVopenSUSE-SU-2021:0516-1 No score

Security update for isync

This update for isync fixes the following issues:

  • isync was updated to version 1.3.5
  • CVE-2021-20247: reject funny mailbox names from IMAP LIST/LSUB (boo#1182488)
Record
openSUSE-SU-2021:0516-1
Updated
2026-11-02
OSVopenSUSE-SU-2021:0533-1 No score

Security update for isync

This update for isync fixes the following issues:

  • isync was updated to version 1.3.5
  • CVE-2021-20247: reject funny mailbox names from IMAP LIST/LSUB (boo#1182488)

This update was imported from the openSUSE:Leap:15.2:Update update project.

Record
openSUSE-SU-2021:0533-1
Updated
2026-11-02
OSVopenSUSE-SU-2024:10866-1 No score

isync-1.4.3-1.2 on GA media

These are all security issues fixed in the isync-1.4.3-1.2 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2024:10866-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
isync
Alpine:v3.13
 before 1.3.5-r0
1.3.5-r0
isync
Alpine:v3.14
 before 1.4.1-r0
1.4.1-r0
isync
Alpine:v3.15
 before 1.4.1-r0
1.4.1-r0
isync
Alpine:v3.16
 before 1.4.1-r0
1.4.1-r0
isync
Alpine:v3.17
 before 1.4.1-r0
1.4.1-r0
isync
Alpine:v3.18
 before 1.4.1-r0
1.4.1-r0
isync
Alpine:v3.19
 before 1.4.1-r0
1.4.1-r0
isync
Alpine:v3.20
 before 1.4.1-r0
1.4.1-r0
isync
Alpine:v3.21
 before 1.4.1-r0
1.4.1-r0
isync
Alpine:v3.22
 before 1.4.1-r0
1.4.1-r0
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Affected packages
PackageAffectedFixed
isync
Alpine:v3.23
 before 1.4.1-r0
1.4.1-r0
isync
Alpine:v3.24
 before 1.4.1-r0
1.4.1-r0
isync
Debian:12
 before 1.3.0-2.1
1.3.0-2.1
isync
Debian:13
 before 1.3.0-2.1
1.3.0-2.1
isync
Debian:14
 before 1.3.0-2.1
1.3.0-2.1
isync
Debian:9
From an advisory covering 3 CVEs
 before 1.2.1-2+deb9u1, plus listed versions
1.2.1-2
1.2.1-2+deb9u1
isync
Ubuntu:16.04:LTS
 All versions, plus listed versions
1.1.2-1
 None known
isync
Ubuntu:18.04:LTS
 All versions, plus listed versions
1.2.1-21.3.0-11.3.0-1build11.3.0-1ubuntu0.18.04.0
 None known
isync
Ubuntu:20.04:LTS
 All versions, plus listed versions
1.3.0-2
 None known
isync
Ubuntu:22.04:LTS
 All versions, plus listed versions
1.3.0-2.21.4.3-11.4.4-11.4.4-31.4.4-3ubuntu0.22.04.1
 None known
isync
Ubuntu:24.04:LTS
 All versions, plus listed versions
1.4.4-51.4.4-5build21.4.4-5build3
 None known
isync
Ubuntu:25.10
 All versions, plus listed versions
1.4.4-5build31.5.1-1ubuntu1
 None known
isync
Ubuntu:26.10
 All versions, plus listed versions
1.5.1-1ubuntu21.5.1-1ubuntu4
 None known
isync
Ubuntu:26.04:LTS
 All versions, plus listed versions
1.5.1-1ubuntu11.5.1-1ubuntu2
 None known
isync
openSUSE:Leap 15.2
 before 1.3.5-lp152.4.3.1
1.3.5-lp152.4.3.1
isync
SUSE:Package Hub 15 SP2
 before 1.3.5-bp152.4.3.1
1.3.5-bp152.4.3.1
isync
openSUSE:Tumbleweed
From an advisory covering 2 CVEs
 before 1.4.3-1.2
1.4.3-1.2

History

History
RecordedChangedSources
affected, facts
affected, aliases, referencesOSV
aliasesEUVD
first indexedCVE List, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-20247 is a high vulnerability (CVSS 7.4) in Mbsync Project Mbsync, published February 23, 2021. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 1.88%, the 79th percentile. Fixed in isync 1.3.5-r0.

References

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