Cyber Resilience

CVE-2021-36539

MediumPublic PoC

Published: 26 January 2023

Published
26 January 2023
Modified
21 November 2024
KEV Added
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Patch
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CVSS Score v3.1 6.5 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
EPSS Score 0.0027 50.3th percentile
Risk Priority 13 60% EPSS · 20% KEV · 20% CVSS

Summary

CVE-2021-36539 is a medium-severity Authorization Bypass Through User-Controlled Key (CWE-639) vulnerability in Instructure Canvas Learning Management Service. Its CVSS base score is 6.5 (Medium).

Operationally, ranked in the top 49.7% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

EU & UK References

Vulnerability details

Instructure Canvas LMS didn't properly deny access to locked/unpublished files when the unprivileged user access the DocViewer based file preview URL (canvadoc_session_url).

CWE(s)
CWE-639

Related Threats

No named actor attribution yet. ATT&CK technique mapping in progress for this CVE.

Affected Assets

instructure
canvas learning management service
≤ 2022-10-15

Mitigating Controls

Likely Mitigating Controls AI

Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.

AC-24 Access Control Decisions
addresses: CWE-639

Per-request decision making makes it harder to bypass authorization using user-controlled keys without proper validation in the decision process.

AC-3 Access Enforcement
addresses: CWE-639

Consistent enforcement of approved authorizations makes bypassing via user-controlled keys ineffective.

References