CVE intelligence and bounded remediation

CVE-2021-20247 — A flaw was found in mbsync before v1.3.5 and v1.4.1

High CVSS 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.

Severity
High
CVSS
7.4 (3.1)
Published
2021-02-23
CISA KEV
Not currently listed
Ecosystem
software/application
Weaknesses
CWE-20, CWE-22

Affected products

  • mbsync_project / mbsync
  • fedoraproject / extra_packages_for_enterprise_linux / 8.0
  • debian / debian_linux / 9.0
  • fedoraproject / fedora / 32
  • fedoraproject / fedora / 33

Showing 5 representative product identities from 6 source matches. Confirm exact affected versions with the linked vendor and NVD evidence.

Matched remediation archetype

Path traversal, unsafe upload, and file handling

This catalog composition supplies bounded fallback guidance. Explicitly reviewed curated workflows load with the complete record below.

Check exposure

  • Trace untrusted filenames, archive entries, URLs, and path segments into read, write, include, extraction, and upload operations.
  • Identify filesystem roots, mount permissions, symbolic-link behavior, archive handling, and whether uploaded content is web-accessible or executable.
  • Review canonicalization and containment checks across supported operating systems and storage backends.

Remediate safely

  • Generate server-side storage identifiers and resolve paths beneath a fixed root using filesystem-aware containment checks.
  • Reject absolute, parent-relative, alternate-separator, device, link, and archive entries that escape the intended root.
  • Store uploads outside executable or served paths, validate type and size, and use private atomic temporary files.

Authoritative sources

Complete CVE record and remediation plan

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