# CVE-2021-43820: Permissions check bypass in Seafile

> Attackers with a valid sync token can access data from any known library by bypassing library-specific authorization checks in Seafile server.

- **Severity:** High 7.4 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 14 Dec 2021
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-m3wc-jv6r-hvv8

## What is CVE-2021-43820?

CVE-2021-43820 is a high-severity missing authorization vulnerability in haiwen seafile-server, published on 14 Dec 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Seafile is an open source cloud storage system. A sync token is used in Seafile file syncing protocol to authorize access to library data. To improve performance, the token is cached in memory in seaf-server. Upon receiving a token from sync client or SeaDrive client, the server checks whether the token exist in the cache. However, if the token exists in cache, the server doesn't check whether it's associated with the specific library in the URL. This vulnerability makes it possible to use any valid sync token to access data from any **known** library. Note that the attacker has to first find out the ID of a library which it has no access to. The library ID is a random UUID, which is not possible to be guessed. There are no workarounds for this issue.

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

## Which versions are affected by CVE-2021-43820?

It affects 1 product.


Products: Seafile Seafile Server.

## How do I fix CVE-2021-43820?

No fix has been published for CVE-2021-43820 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-43820 being exploited?

There is no known exploitation of CVE-2021-43820 in the wild and no public exploit code.

## Other vulnerabilities in haiwen seafile-server

- [CVE-2014-5443](https://insights.sbomify.com/CVE-2014-5443/): Privilege escalation in n/a (high 7.8)
- [CVE-2025-65516](https://insights.sbomify.com/CVE-2025-65516/): Cross-site scripting in n/a (medium 6.1)
- [CVE-2026-30587](https://insights.sbomify.com/CVE-2026-30587/): Seafile Server has multiple stored XSS vulnerabilities (medium 5.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-43820 and fix it if it is affected.

What it is: CVE-2021-43820 is a high-severity missing authorization vulnerability in haiwen seafile-server, published on 14 Dec 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-43820 in the wild and no public exploit code.

Affected product: haiwen seafile-server. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2021-43820/ (Markdown: https://insights.sbomify.com/CVE-2021-43820/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-43820
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-43820
- OSV: https://osv.dev/vulnerability/CVE-2021-43820

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-43820/
Summaries are generated and may contain mistakes; the official description above is the record.