# CVE-2017-0881: Missing authorization in Zulip Server Versions 1.4.2 and below

> Authenticated users can bypass invitation requirements to subscribe to private streams, exposing private data.

- **Severity:** Medium 4.3 (`CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:L/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:** No
- **Published:** 28 Mar 2017
- **Updated:** 5 Aug 2024
- **Also known as:** GHSA-435h-5vch-xh86

## What is CVE-2017-0881?

CVE-2017-0881 is a medium-severity missing authorization vulnerability in Zulip Server Versions 1.4.2 and below, published on 28 Mar 2017. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

An error in the implementation of an autosubscribe feature in the check_stream_exists route of the Zulip group chat application server before 1.4.3 allowed an authenticated user to subscribe to a private stream that should have required an invitation from an existing member to join. The issue affects all previously released versions of the Zulip server.

Weakness: CWE-863 (Incorrect Authorization), CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor)

## Which versions are affected by CVE-2017-0881?

It affects 1 product.


Products: Zulip Zulip Server.

## How do I fix CVE-2017-0881?

No fix has been published for CVE-2017-0881 yet. Limit exposure of the affected software until one is available.

## Is CVE-2017-0881 being exploited?

There is no known exploitation of CVE-2017-0881 in the wild and no public exploit code.

## Other vulnerabilities in Zulip Server Versions 1.4.2 and below

- [CVE-2019-18933](https://insights.sbomify.com/CVE-2019-18933/): Information disclosure in n/a (critical 9.8)
- [CVE-2020-15070](https://insights.sbomify.com/CVE-2020-15070/): Code injection in n/a (high 8.8)
- [CVE-2017-0910](https://insights.sbomify.com/CVE-2017-0910/): Missing authorization in Zulip Server (high 8.8)
- [CVE-2025-31478](https://insights.sbomify.com/CVE-2025-31478/): Zulip Authentication Backend Configuration Bypass (high 8.2)
- [CVE-2023-33186](https://insights.sbomify.com/CVE-2023-33186/): Cross-site scripting vulnerability in Zulip Server development branch via topic tooltip (high 8.2)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2017-0881 and fix it if it is affected.

What it is: CVE-2017-0881 is a medium-severity missing authorization vulnerability in Zulip Server Versions 1.4.2 and below, published on 28 Mar 2017. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2017-0881 in the wild and no public exploit code.

Affected product: Zulip Server Versions 1.4.2 and below. 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-2017-0881/ (Markdown: https://insights.sbomify.com/CVE-2017-0881/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2017-0881
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2017-0881
- OSV: https://osv.dev/vulnerability/CVE-2017-0881

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From sbomify Insights: https://insights.sbomify.com/CVE-2017-0881/
Summaries are generated and may contain mistakes; the official description above is the record.