CVE-2021-36403

Moodle has a Hidden Functionality vulnerability

5.3 MediumFix available

In Moodle, in some circumstances, email notifications of messages could have the link back to the original message hidden by HTML, which may pose a phishing risk.

Attack profile

How easy it is to exploit

Attack vector: Network
Complexity: Low
Privileges needed: None
User interaction: None

What an attacker can affect

Confidentiality: None
Integrity: Low
Availability: None

Exploit likelihood

0.53%Up 0.5 points since Mar 7, 2023

What each source reports

NVD Score used 5.3

In Moodle, in some circumstances, email notifications of messages could have the link back to the original message hidden by HTML, which may pose a phishing risk.

Record: CVE-2021-36403
CVSS 3.1: 5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Weakness: CWE-912
Updated: 2026-11-02

CVE List 5.3

In Moodle, in some circumstances, email notifications of messages could have the link back to the original message hidden by HTML, which may pose a phishing risk.

Record: CVE-2021-36403
CVSS 3.1: 5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Weakness: CWE-912
Updated: 2026-11-02

EUVDEUVD-2023-1048 5.3

In Moodle, in some circumstances, email notifications of messages could have the link back to the original message hidden by HTML, which may pose a phishing risk.

Record: EUVD-2023-1048
CVSS 3.1: 5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Updated: 2026-11-02

GitHub AdvisoriesGHSA-j9cw-5cpj-9qj5 5.3

Moodle has a Hidden Functionality vulnerability

In Moodle, in some circumstances, email notifications of messages could have the link back to the original message hidden by HTML, which may pose a phishing risk.

Record: GHSA-j9cw-5cpj-9qj5
CVSS 3.1: 5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Weakness: CWE-912
Updated: 2026-11-02

OSV 5.3

In Moodle, in some circumstances, email notifications of messages could have the link back to the original message hidden by HTML, which may pose a phishing risk.

Record: CVE-2021-36403
CVSS 3.1: 5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Updated: 2026-11-02

OSVGHSA-j9cw-5cpj-9qj5 5.3

Moodle has a Hidden Functionality vulnerability

In Moodle, in some circumstances, email notifications of messages could have the link back to the original message hidden by HTML, which may pose a phishing risk.

Record: GHSA-j9cw-5cpj-9qj5
CVSS 3.1: 5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Weakness: CWE-912
Updated: 2026-11-02

OSVUBUNTU-CVE-2021-36403 5.3

In Moodle, in some circumstances, email notifications of messages could have the link back to the original message hidden by HTML, which may pose a phishing risk.

Record: UBUNTU-CVE-2021-36403
CVSS 3.1: 5.3 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Updated: 2026-11-02

OSVBIT-moodle-2021-36403 No score

In Moodle, in some circumstances, email notifications of messages could have the link back to the original message hidden by HTML, which may pose a phishing risk.

Record: BIT-moodle-2021-36403
Updated: 2026-11-02

Affected products

moodle

Affected packages

Affected packages
Package	Affected	Fixed
`moodle/moodle` Packagist	3.11.0-beta up to 3.11.1	3.11.1
`moodle/moodle` Packagist	3.10.0-beta up to 3.10.5	3.10.5
`moodle/moodle` Packagist	before 3.9.8	3.9.8
`moodle` Bitnami	before 3.9.8, 3.10.0 up to 3.10.5, 3.11.0 up to 3.11.1	3.9.83.10.53.11.1
`moodle/moodle` Packagist	3.11.0-beta up to 3.11.1, plus listed versions v3.11.0v3.11.0-betav3.11.0-rc1v3.11.0-rc2	3.11.1
`moodle/moodle` Packagist	3.10.0-beta up to 3.10.5, plus listed versions v3.10.0v3.10.0-betav3.10.0-rc1v3.10.0-rc2v3.10.1v3.10.2v3.10.3v3.10.4	3.10.5
`moodle/moodle` Packagist	before 3.9.8, plus listed versions v2.3.10v2.3.11v2.3.4v2.3.5v2.3.6 Show 45 moreShow less v2.3.7v2.3.8v2.3.9v2.4.0v2.4.0-rc1v2.4.1v2.4.10v2.4.11v2.4.2v2.4.3v2.4.4v2.4.5v2.4.6v2.4.7v2.4.8v2.4.9v2.5.0v2.5.0-betav2.5.0-rc1v2.5.1v2.5.2v2.5.3v2.5.4v2.5.5v2.5.6v2.5.7v2.5.8v2.5.9v2.6.0v2.6.0-betav2.6.0-rc1v2.6.1v2.6.10v2.6.11v2.6.2v2.6.3v2.6.4v2.6.5v2.6.6v2.6.7v2.6.8v2.6.9v2.7.0v2.7.0-betav2.7.0-rc1	3.9.8
`moodle` Ubuntu:Pro:16.04:LTS	All versions, plus listed versions 2.7.9+dfsg-12.7.10+dfsg-12.7.11+dfsg-12.7.11+dfsg-22.7.12+dfsg-13.0.3+dfsg-0ubuntu13.0.3+dfsg-0ubuntu1+esm1	None known
`moodle` Ubuntu:Pro:18.04:LTS	All versions, plus listed versions 3.0.3+dfsg-0ubuntu13.0.3+dfsg-0ubuntu1+esm1	None known

History

History
Recorded	Changed	Sources
Nov 2, 2026	first indexed	CVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2021-36403 is a medium vulnerability (CVSS 5.3) in Moodle, published March 6, 2023. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.53%, the 45th percentile. Fixed in moodle/moodle 3.11.1.

References

This page doesn't list everything

Left out here: 205 versions. The JSON record has them.