# CVE-2021-36539: Missing authorization in n/a

> Unprivileged users can access locked or unpublished files via DocViewer preview URLs, exposing sensitive content.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 26 Jan 2023
- **Updated:** 4 Aug 2024
- **Also known as:** BIT-canvaslms-2021-36539, GHSA-pw89-gxgv-mjvm

## What is CVE-2021-36539?

CVE-2021-36539 is a medium-severity missing authorization vulnerability in n/a, published on 26 Jan 2023. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Instructure Canvas LMS didn't properly deny access to locked/unpublished files when the unprivileged user access the DocViewer based file preview URL (canvadoc_session_url).

Weakness: CWE-639 (Authorization Bypass Through User-Controlled Key)

## Which versions are affected by CVE-2021-36539?

1 open source package ship an affected version, including canvaslms. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `canvaslms` | Bitnami | All versions | 2022-10-15.0.0 |

Products: Instructure Canvas Learning Management Service.

## How do I fix CVE-2021-36539?

Upgrade canvaslms to 2022-10-15.0.0 or later.

## Is CVE-2021-36539 being exploited?

There is no known exploitation of CVE-2021-36539 in the wild and no public exploit code.

## Other vulnerabilities in n/a

- [CVE-2020-5775](https://insights.sbomify.com/CVE-2020-5775/): Server-side request forgery in Instructure Canvas Learning Management System (LMS) (medium 5.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-36539 and fix it if it is affected.

What it is: CVE-2021-36539 is a medium-severity missing authorization vulnerability in n/a, published on 26 Jan 2023. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-36539 in the wild and no public exploit code.

Affected packages and fixed versions:
- canvaslms (Bitnami): affected all versions; fixed in 2022-10-15.0.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-36539/ (Markdown: https://insights.sbomify.com/CVE-2021-36539/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-36539
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-36539
- OSV: https://osv.dev/vulnerability/CVE-2021-36539

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-36539/
Summaries are generated and may contain mistakes; the official description above is the record.