CVE-2021-20183: Moodle/moodle Cross-Site Scripting Vulnerability

MODERATE
Advisory Identifier: GHSA-xhfx-rm8q-c3xv
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CVSS 5.4
CWE-79
Published
Advisory Summary

CVE-2021-20183 is a MODERATE (CVSS 5.4) cross-site scripting vulnerability (CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')) affecting Moodle/moodle libraries in the Packagist ecosystem. The issue involves moodle vulnerable to reflected cross-site scripting. Remediation is available by upgrading affected packages to version 4.0.0-beta.

CVE-2021-20183 at a Glance

CVE Identifier CVE-2021-20183
GHSA Identifier GHSA-xhfx-rm8q-c3xv
Severity MODERATE
CVSS v3.1 Base Score 5.4
CWE Classification CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Affected Product Moodle/moodle
Package Ecosystem Packagist
Published Date
Last Updated

Security Impact

CVSS: 5.4

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction Required (UI:R)
Scope Unchanged (S:U)
Confidentiality Low (C:L)
Integrity Low (I:L)
Availability None (A:N)

How to Fix CVE-2021-20183

To remediate this vulnerability, upgrade all affected Moodle/moodle dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

moodle/moodle fixed: 4.0.0-beta 
Upgrade moodle/moodle to 4.0.0-beta
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for moodle/moodle

How to Check if You Are Affected

To determine whether your application is affected by CVE-2021-20183, inspect your project dependencies for Moodle/moodle:

inspect dependencies for moodle/moodle

Analyze the terminal output to locate any version of Moodle/moodle in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.0.0-beta), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'), where the product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. In Moodle/moodle, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

It was found in Moodle before version 4.0.0-beta that some search inputs were vulnerable to reflected Cross-site Scripting (XSS) due to insufficient escaping of search queries.

CVE-2021-20183 Affected Moodle/moodle Versions

1 component(s)
Fixed Versions:
4.0.0-beta
Product / Package Ecosystem Affected Versions Fixed Version
moodle/moodle
 Packagist
≥ 3.10
< 4.0.0-beta
4.0.0-beta

References

NVD — CVE-2021-20183 NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-20183
Security Fix Commit FIX COMMIT
https://github.com/moodle/moodle/commit/dc9de7b0d487b73c23c221dc0b8b6e01654921f3
moodle.org/mod/forum/discuss.p... WEB
https://moodle.org/mod/forum/discuss.php?d=417166

Frequently Asked Questions

What is CVE-2021-20183?
CVE-2021-20183 is a security vulnerability in Moodle/moodle involving Moodle Vulnerable to Reflected Cross-site Scripting under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting').
Which Moodle/moodle versions are affected?
Affected versions include releases prior to 4.0.0-beta across affected packages: moodle/moodle.
What version fixes CVE-2021-20183?
Upgrading to 4.0.0-beta (or the latest patched release for your respective branch) resolves the vulnerability.
Is moodle/moodle affected?
Yes, moodle/moodle is affected in releases prior to 4.0.0-beta. Upgrade your dependency to 4.0.0-beta or later.
What is the CVSS score of CVE-2021-20183?
CVE-2021-20183 has a CVSS v3.1 base score of 5.4 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N.
What CWE is associated with CVE-2021-20183?
CVE-2021-20183 is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.).
How can I check Packagist dependencies for CVE-2021-20183?
Run the dependency tree command: 'inspect dependencies for moodle/moodle'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-xhfx-rm8q-c3xv",
  "modified" : "2023-09-12T13:17:21Z",
  "published" : "2022-05-24T17:40:31Z",
  "aliases" : [ "CVE-2021-20183" ],
  "summary" : "Moodle Vulnerable to Reflected Cross-site Scripting",
  "details" : "It was found in Moodle before version 4.0.0-beta that some search inputs were vulnerable to reflected Cross-site Scripting (XSS) due to insufficient escaping of search queries.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "moodle/moodle"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "3.10"
      }, {
        "fixed" : "4.0.0-beta"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2021-20183"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/moodle/moodle/commit/dc9de7b0d487b73c23c221dc0b8b6e01654921f3"
  }, {
    "type" : "WEB",
    "url" : "https://moodle.org/mod/forum/discuss.php?d=417166"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-79" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2023-07-10T22:23:56Z",
    "nvd_published_at" : "2021-01-28T19:15:00Z"
  }
}