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 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.

Published: 2022-02-16 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-3578 is rated Moderate Risk (51.5/100): CVSS High severity, with medium exploitation likelihood (EPSS 0.98%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-3578

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.85% 0.98% +0.13%
2 2026-05-27 1.92% 0.85% -1.06%
3 2026-03-26 — 1.92% —

Full EPSS history (26 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-3578

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.8 3.1 HIGH
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 1.8 5.9 [email protected]
7.2 2.0 HIGH
AV:L/AC:L/Au:N/C:C/I:C/A:C Click to expand
Access vector (AV:L)
Requires local access to the target system.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:C)
Complete confidentiality impact.
Integrity impact (I:C)
Complete integrity impact.
Availability impact (A:C)
Complete availability impact.
 3.9 10.0 [email protected]

Weakness enumeration for CVE-2021-3578

OS Trackers for CVE-2021-3578

vendor priority summary link
alpine high CVE-2021-3578: 1 source package rows (isync); 7 state rows across 7 repos (3.17-community, 3.18-community, 3.19-community, 3.20-community, 3.21-community, 3.22-community, edge-community); fixed 7, open 0. https://security.alpinelinux.org/vuln/CVE-2021-3578
debian not yet assigned CVE-2021-3578 not yet assigned priority: Debian including 1 source packages (isync), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-3578
gentoo normal CVE-2021-3578: 1 GLSA(s) (202208-15), 1 atom(s) (net-mail/isync); latest impact normal. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-3578
ubuntu medium CVE-2021-3578 medium priority: Ubuntu including 1 source packages (isync), 16 status rows across 16 suites (bionic, focal, groovy, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): ignored 8, needs-triage 7, DNE 1. https://ubuntu.com/security/CVE-2021-3578

Affected software / configurations for CVE-2021-3578

Vendor Product Version Raw CPE
isync_project isync < 1.3.6 cpe:2.3:a:isync_project:isync:*:*:*:*:*:*:*:*
isync_project isync 1.4.0 cpe:2.3:a:isync_project:isync:1.4.0:*:*:*:*:*:*:*
isync_project isync 1.4.1 cpe:2.3:a:isync_project:isync:1.4.1:*:*:*:*:*:*:*
fedoraproject fedora 33 cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*
fedoraproject fedora 34 cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
debian debian_linux 9.0 cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*

References for CVE-2021-3578

URL Tags
http://www.openwall.com/lists/oss-security/2021/06/07/1 Mailing List Patch Third Party Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=1961710 Not Applicable
https://bugzilla.redhat.com/show_bug.cgi?id=1967397 Issue Tracking Patch Third Party Advisory
https://github.blog/2021-06-10-privilege-escalation-polkit-root-on-linux-with-bug/ Not Applicable
https://lists.debian.org/debian-lts-announce/2022/07/msg00001.html Mailing List Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RPIDLIJKNRJHUVBCL7QGAPAAVPIHQGXK/
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/U75UFEWRAZYKVL5NHMPBUOLWN3WXTOEI/
https://security.gentoo.org/glsa/202208-15 Third Party Advisory
https://www.openwall.com/lists/oss-security/2021/06/07/1 Mailing List Patch Third Party Advisory
cvelogic Threat Intelligence