Moodle vulnerable to stored Cross-site Scripting

published 2023-05-16 3 y ago modified 2026-09-08 2 mo ago also BIT-moodle-2021-27131 , EUVD-2023-1633 , GHSA-w2pm-fr62-jgv4

cvss: 5.4; version 3.1, NVD
cisa kev: Not listed; not in CISA's catalog
epss: 0.7%; EPSS 0.7% chance of exploitation in 30 days, percentile 52%
public exploits: 0; none known

Moodle 3.10.1 is vulnerable to persistent/stored cross-site scripting (XSS) due to the improper input sanitization on the "Additional HTML Section" via "Header and Footer" parameter in /admin/settings.php. This vulnerability is leading an attacker to steal admin and all user account cookies by storing the malicious XSS payload in Header and Footer. NOTE: this is disputed by the vendor because the "Additional HTML Section" for "Header and Footer" can only be supplied by an administrator, who is intentionally allowed to enter unsanitized input (e.g., site-specific JavaScript).

Patch / fix

fixed in 1

bitnami moodle 3.10.2

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-27131 updated 2026-01-13

moodle: stored xss

Red Hat All currently supported Red Hat products
not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

0.69% chance of exploitation in the next 30 days, higher than 52% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

github.com https://github.com/p4nk4jv/CVEs-Assigned/blob/master/Moodle-3.10.1-CVE-2021-27131.md referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
GitHub	3.1	5.4	CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
NVD	3.1	5.4	CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
OSV	3.1	5.4	CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

Affected packages

ecosystem	package	affected	fixed in
packagist	moodle/moodle	<=3.10.1	no fix listed
bitnami	moodle	>=3.10.1, <3.10.2	3.10.2

Classification

Weakness

CWE-79 Improper Neutralization of Input During Web Page Generation

References

github.com /p4nk4jv/CVEs-Assigned/blob/master/Moodle-3.10.1-CVE-2021-27131.md
web, exploit, evidence
github.com /moodle/moodle
package, product, web
docs.moodle.org /402/en/Risks
web
nvd.nist.gov /vuln/detail/CVE-2021-27131
advisory, web

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary