What is CVE-2021-3964?

CVE-2021-3964 is a medium-severity vulnerability in Elgg, classified under Authorization Bypass Through User-Controlled Key. CVSS score: 5.9/10. Published 2021-12-01.

How severe is CVE-2021-3964?

Medium severity. CVSS v3 base score is 5.9 out of 10.

Auth bypass in Elgg

CVE-2021-3964

elgg is vulnerable to Authorization Bypass Through User-Controlled Key

Vulnerability class: IDOR (Insecure Direct Object Reference)

Published 2021-12-01 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 5.9 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N.

EPSS exploit prediction

EPSS: 0.008 (55.0th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 55th percentile — 55.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.008 · newest: 0.008 · change: +0.000

Affected products

Elgg
Elgg Elgg/elgg — versions unspecified

Weakness classification (CWE)

CWE-639 — Authorization Bypass Through User-Controlled Key

References

huntr.dev/bounties/a4df45d6-b739-4299-967f-c960b569383a (Exploit, Patch, Third Party Advisory)
github.com/elgg/elgg/commit/d9fcad76ee380ea17edd61d13d0f87828ea3f744 (Patch, Third Party Advisory)

Frequently asked questions

What is CVE-2021-3964?: CVE-2021-3964 is a medium-severity vulnerability in Elgg, classified under Authorization Bypass Through User-Controlled Key. CVSS score: 5.9/10. Published 2021-12-01.
How severe is CVE-2021-3964?: Medium severity. CVSS v3 base score is 5.9 out of 10.