CVE-2023-23921Network attack vector

Victim-session script execution via unsanitized returnurl

Published Feb 17, 2023 · Updated Aug 2, 2024

Reflected XSS in affected Moodle LMS releases allows remote attackers to execute script in a victim's browser through crafted returnurl parameters. Affected request handlers return insufficiently sanitized returnurl values in generated pages, allowing supplied HTML and script to run in the site's origin. Exploitation requires a victim to follow a crafted link; successful script execution can read or alter browser-accessible data in that victim's Moodle session.

CVSS severity6.1
Medium
EPSS probability0.81%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Reflected XSS in affected Moodle LMS releases allows remote attackers to execute script in a victim's browser through crafted returnurl parameters. Affected request handlers return insufficiently sanitized returnurl values in generated pages, allowing supplied HTML and script to run in the site's origin. Exploitation requires a victim to follow a crafted link; successful script execution can read or alter browser-accessible data in that victim's Moodle session.

The record

CVE
CVE-2023-23921
Published
Feb 17, 2023
Updated
Aug 2, 2024
Vendor
Moodle
Product
Moodle LMS
Classifications
CWE-79, T1204.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 17, 2023CVE publishedPublication date reported by the CVE source.
  2. Aug 2, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <3.9.19
  2. Affected versionversion=3.11.0 <3.11.12
  3. Affected versionversion=4.0.0 <4.0.6
  4. Affected versionversion=4.1.0 <4.1.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Moodle · Moodle LMSversion=0 <3.9.19; version=3.11.0 <3.11.12; version=4.0.0 <4.0.6; version=4.1.0 <4.1.1

Published CVSS scores

6.1GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
6.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1204.001User Execution: Malicious Link

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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