What is CVE-2021-36539?

CVE-2021-36539 is a medium-severity vulnerability in Instructure Canvas Learning Management Service, classified under Authorization Bypass Through User-Controlled Key. CVSS score: 6.5/10. Published 2023-01-26.

How severe is CVE-2021-36539?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Auth bypass in Instructure Canvas Learning Management Service

CVE-2021-36539

Instructure Canvas LMS didn't properly deny access to locked/unpublished files when the unprivileged user access the DocViewer based file preview URL (canvadoc_session_url).

Vulnerability class: IDOR (Insecure Direct Object Reference)

Published 2023-01-26 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N.

EPSS exploit prediction

EPSS: 0.009 (57.5th percentile), scored 2026-10-04.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 58th percentile — 57.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.009 · newest: 0.009 · change: 0.000

Affected products

Instructure Canvas Learning Management Service

Weakness classification (CWE)

CWE-639 — Authorization Bypass Through User-Controlled Key

References

github.com/instructure/canvas-lms/issues/1905 (Exploit, Third Party Advisory)
github.com/gaukas/instructure-canvas-file-oracle (Exploit, Third Party Advisory)

Frequently asked questions

What is CVE-2021-36539?: CVE-2021-36539 is a medium-severity vulnerability in Instructure Canvas Learning Management Service, classified under Authorization Bypass Through User-Controlled Key. CVSS score: 6.5/10. Published 2023-01-26.
How severe is CVE-2021-36539?: Medium severity. CVSS v3 base score is 6.5 out of 10.