CVE-2021-20247Network attack vector

Mailbox data theft and deletion via path traversal

Published Feb 23, 2021 · Updated Aug 3, 2024

Path traversal in Isync Project mbsync before 1.3.5 and 1.4.0 allows remote attackers controlling an IMAP server to steal or delete local mail. The IMAP LIST/LSUB handler accepts '..' components in server-supplied mailbox names and maps them across the synchronization channel without rejecting traversal outside the selected mailbox. The channel Pattern must contain '*'; local Maildir impact also depends on SubFolders mode, and exposed messages can be copied to the server or deleted.

CVSS severity7.4
High
EPSS probability1.88%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Path traversal in Isync Project mbsync before 1.3.5 and 1.4.0 allows remote attackers controlling an IMAP server to steal or delete local mail. The IMAP LIST/LSUB handler accepts '..' components in server-supplied mailbox names and maps them across the synchronization channel without rejecting traversal outside the selected mailbox. The channel Pattern must contain '*'; local Maildir impact also depends on SubFolders mode, and exposed messages can be copied to the server or deleted.

The record

CVE
CVE-2021-20247
Published
Feb 23, 2021
Updated
Aug 3, 2024
Vendor
Isync Project
Product
mbsync
Classifications
CWE-22, CWE-20, T1005
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 23, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=before 1.35
  2. Affected versionversion=before 1.4.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Isync Project · mbsyncversion=before 1.35; version=before 1.4.1

Published CVSS scores

5.8NIST NVDAV:N/AC:M/Au:N/C:P/I:P/A:N
7.4NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-22Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
CWE-20Improper Input Validation
T1005Data from Local System

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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