CVE-2021-3943

A flaw was found in Moodle in versions 3.11 to 3.11.3, 3.10 to 3.10.7, 3.9 to 3.9.10 and earlier unsupported versions. A remote code execution risk when restoring backup files was identified.

Published: 2021-11-22 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-3943 is rated High Risk (69/100): CVSS Critical severity, with medium exploitation likelihood (EPSS 2.38%). EPSS rose +1.19% over the last day, indicating growing attacker interest. High exploitation likelihood—assess exposure and prioritize 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-2021-3943

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 1.20% 2.38% +1.19%
2 2025-12-28 1.15% 1.20% +0.05%
3 2025-12-27 — 1.15% —

Full EPSS history (24 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-3943

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.8 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
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:N)
No account or special rights needed—anonymous or random user is enough.
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.
 3.9 5.9 [email protected]
7.5 2.0 HIGH
AV:N/AC:L/Au:N/C:P/I:P/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:P)
Partial availability impact.
 10.0 6.4 [email protected]

Weakness enumeration for CVE-2021-3943

GitHub Security Advisory for CVE-2021-3943

GHSA-8jhp-2gcr-qw96 · Severity: critical · Ecosystem: composer — Moodle vulnerable to RCE via unsafe deserialization

OS Trackers for CVE-2021-3943

vendor priority summary link
ubuntu medium CVE-2021-3943 medium priority: Ubuntu including 1 source packages (moodle), 4 status rows across 4 suites (bionic, trusty, upstream, xenial): needs-triage 3, ignored 1. https://ubuntu.com/security/CVE-2021-3943

Affected software / configurations for CVE-2021-3943

Vendor Product Version Raw CPE
moodle moodle >= 3.9.0, <= 3.9.10 cpe:2.3:a:moodle:moodle:*:*:*:*:*:*:*:*
moodle moodle >= 3.10.0, <= 3.10.7 cpe:2.3:a:moodle:moodle:*:*:*:*:*:*:*:*
moodle moodle >= 3.11.0, <= 3.11.3 cpe:2.3:a:moodle:moodle:*:*:*:*:*:*:*:*

References for CVE-2021-3943

URL Tags
https://bugzilla.redhat.com/show_bug.cgi?id=2021963 Issue Tracking Third Party Advisory
https://moodle.org/mod/forum/discuss.php?d=429095 Patch Vendor Advisory
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