CVE-2021-36539Public exploitNetwork attack vector

File disclosure via unchecked DocViewer session URLs

Published Jan 26, 2023 · Updated Aug 4, 2024

Authorization bypass in Instructure Canvas LMS before 2022-10-15 allows remote authenticated users to read locked course files. The course-files API returns a valid canvadoc_session_url for any file ID in an enrolled course without enforcing the file's publication or lock state, and that URL redirects to DocViewer content. Student-level course enrollment and API access are required; guessed or known file IDs expose file contents but do not permit modification.

CVSS severity6.5
Medium
EPSS probability0.87%
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 Instructure Canvas LMS before 2022-10-15 allows remote authenticated users to read locked course files. The course-files API returns a valid canvadoc_session_url for any file ID in an enrolled course without enforcing the file's publication or lock state, and that URL redirects to DocViewer content. Student-level course enrollment and API access are required; guessed or known file IDs expose file contents but do not permit modification.

The record

CVE
CVE-2021-36539
Published
Jan 26, 2023
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-639, T1213
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jan 26, 2023CVE 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-639Authorization Bypass Through User-Controlled Key
T1213Data from Information Repositories

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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