CVE-2021-3578: A flaw was found in mbsync before v1.3.6 and v1.4.2, where an unchecked pointer cast allows a malicious or com

Q: How do I fix CVE-2021-3578?

isync: upgrade to 1.3.6; fedora: mitigate or apply the listed mitigation; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Q: Is CVE-2021-3578 being exploited?

CVE-2021-3578 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-3578 affect?

CVE-2021-3578 affects isync, fedora, debian linux. Severity is high (CVSS 7.8). A flaw was found in mbsync before v1.3.6 and v1.4.2, where an unchecked pointer cast allows a malicious or compromised server to write an arbitrary integer value past the end of a heap-allocated structure by issuing an unexpected APPENDUID

Q: How urgent is CVE-2021-3578?

Priority 48/100. High severity; On your watchlist

This month

HIGH 7.8WATCHLISTUPGRADEMITIGATEMITIGATE

CVE-2021-3578 is a high-severity flaw (CVSS 7.8) affecting isync, fedora, debian linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

A flaw was found in mbsync before v1.3.6 and v1.4.2, where an unchecked pointer cast allows a malicious or compromised server to write an arbitrary integer value past the end of a heap-allocated structure by issuing an unexpected APPENDUID response. This could be plausibly exploited for remote code execution on the client.

Why this priority

High severity
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	7.8 (High)
Attack vector	Local
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	1.0% (top 36%)
CISA exploited list	No
Weakness	CWE-704
Published	2022-02-16
Last modified	2026-06-17

Publisher (CNA): Red Hat, Inc. · Vendor: debian · fedoraproject · isync project

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2022-02-16 19:15 UTCPublished CVE record published
2026-06-17 04:05 UTCUpdated Record last modified

isync project isync UPGRADE

Affected: < 1.3.6 · 1.4.0 · 1.4.1

Fixed in: 1.3.6

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy isync || rpm -q isync || isync --version

2. UPGRADE to 1.3.6 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade isync

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade isync

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

fedoraproject fedora MITIGATE

Affected: 33 · 34

Fixed in: no fixed release known

Safe to downgrade to: a release before 33

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

debian debian linux MITIGATE

Affected: 9.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 9.0

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-3578?

isync: upgrade to 1.3.6; fedora: mitigate or apply the listed mitigation; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-3578 being exploited?

CVE-2021-3578 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-3578 affect?

CVE-2021-3578 affects isync, fedora, debian linux. Severity is high (CVSS 7.8). A flaw was found in mbsync before v1.3.6 and v1.4.2, where an unchecked pointer cast allows a malicious or compromised server to write an arbitrary integer value past the end of a heap-allocated structure by issuing an unexpected APPENDUID

How urgent is CVE-2021-3578?

Priority 48/100. High severity; On your watchlist

Software pages

Debian vulnerabilities

Related CVEs

CVE-2021-44143 CRITICAL 9.8 UPGRADE MITIGATE A flaw was found in mbsync in isync 1.4.0 through 1.4.3
CVE-2021-3657 CRITICAL 9.8 UPGRADE MITIGATE A flaw was found in mbsync versions prior to 1.4.4

References

← Back to latest CVEs