CVE-2021-40691Network attack vector

Session hijacking via failed logout invalidation

Published Jan 21, 2022 · Updated Aug 4, 2024

Improper authentication in Moodle LMS 3.11 through 3.11.2 allows remote attackers to reuse Shibboleth sessions after users log out. The Shibboleth plugin leaves Moodle sessions valid after logout instead of invalidating them, so a previously obtained session identifier remains accepted. Shibboleth authentication must be enabled, and the attacker must possess an authenticated user's session identifier; the plugin is disabled by default.

CVSS severity4.3
Medium
EPSS probability0.71%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper authentication in Moodle LMS 3.11 through 3.11.2 allows remote attackers to reuse Shibboleth sessions after users log out. The Shibboleth plugin leaves Moodle sessions valid after logout instead of invalidating them, so a previously obtained session identifier remains accepted. Shibboleth authentication must be enabled, and the attacker must possess an authenticated user's session identifier; the plugin is disabled by default.

The record

CVE
CVE-2021-40691
Published
Jan 21, 2022
Updated
Aug 4, 2024
Vendor
Moodle
Product
Moodle LMS
Classifications
T1539
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 21, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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=3.11 to 3.11.2, 3.10 to 3.10.6, 3.9 to 3.9.9 and earlier unsupported versions

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Moodle · Moodle LMSversion=3.11 to 3.11.2, 3.10 to 3.10.6, 3.9 to 3.9.9 and earlier unsupported versions

Published CVSS scores

4.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1539Steal Web Session Cookie

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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