CVE-2021-3964Network attack vector

Unauthorized group membership changes via unchecked GUIDs

Published Dec 1, 2021 · Updated Aug 3, 2024

Authorization bypass in Elgg before 3.3.22 allows remote attackers to alter group membership through crafted membership actions. Four membership handlers trust request-supplied user and group GUIDs and perform join, leave, invitation, or request changes without checking edit rights. A reachable action endpoint and valid user and group GUIDs are required; the bounded consequence is unauthorized group-membership modification.

CVSS severity5.9
Medium
EPSS probability0.78%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authorization bypass in Elgg before 3.3.22 allows remote attackers to alter group membership through crafted membership actions. Four membership handlers trust request-supplied user and group GUIDs and perform join, leave, invitation, or request changes without checking edit rights. A reachable action endpoint and valid user and group GUIDs are required; the bounded consequence is unauthorized group-membership modification.

The record

CVE
CVE-2021-3964
Published
Dec 1, 2021
Updated
Aug 3, 2024
Vendor
Elgg Foundation
Product
Elgg
Classifications
CWE-639, T1098
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 1, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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?

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  1. Affected versionversion=unspecified <3.3.22

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Elgg Foundation · Elggversion=unspecified <3.3.22

Published CVSS scores

5.9GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/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.

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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

CWE-639Authorization Bypass Through User-Controlled Key
T1098Account Manipulation

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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