CVE-2022-39329 - Sensitive Information Disclosure in Nextcloud Server

Nextcloud is one of the most popular open-source self-hosted file servers in the world. If you use Nextcloud to sync files, collaborate with your team, or simply back up your data at home, you probably rely on its promise to keep your private documents secure. However, in 2022, a critical vulnerability—CVE-2022-39329—was discovered that put confidential data at risk.

Let's break down this vulnerability in everyday language, look at how it works, review some example code, and discuss what you should do to protect yourself.

What is CVE-2022-39329?

CVE-2022-39329 is a security vulnerability found in Nextcloud Server and Nextcloud Enterprise Server versions prior to 23..9 and 24..5. This flaw allowed certain types of information to be exposed, and crucially, administrators had no way to control or fix this risk unless they had direct database access. In simple terms: data could leak even if you locked down your server.

Where’s the official info?

- Github Security Advisory
- Nextcloud Security Advisory
- NVD Entry

Who is Vulnerable?

Anyone running Nextcloud Server or Enterprise Server before 23..9 or 24..5. This affects home users, self-hosted setups, and large organizations.

If you haven’t updated at least to 23..9 or 24..5, you are at risk.

- Normally, administrators can set permissions, users can control their files, and the server software keeps private things private.
- In vulnerable versions, certain sensitive information (for example, the ID or “token” of a file share) could be exposed by mistake, even when it should not be accessible—and the admin panel could not fix it!

No patch, config tweak, or workaround was available for old versions.

- Attackers might use this flaw to learn about shared link tokens or access mappings in the system, potentially leading to further attacks.

A “share token” is like a secret code you give to someone to access a private file. Normally, only the right people should know this code!

In vulnerable Nextcloud versions, a regular user (or attacker with partial access) could run a request or database query and reveal information about shares or users that they shouldn’t be able to see.

// Example: Fetch all file share tokens from the database
// Only admins or owners should see these, but in the vulnerable version
// someone with enough access could dump them

$db = new \OC\DB\Connection($connectionParams);
// This is DANGEROUS and should not be possible for regular users
$query = 'SELECT id, token, uid_owner FROM oc_share';
$shares = $db->executeQuery($query);

foreach ($shares as $share) {
    echo "Share ID: " . $share['id'] . " Token: " . $share['token'] . " Owner: " . $share['uid_owner'] . "\n";
}

This is purely for illustration—Nextcloud doesn’t run exactly like this, but it gives you an idea: if you can get access to this info, you can steal or misuse private links.

Exploit Scenario

Say you’re a regular user on a shared Nextcloud instance. You should not be able to see other users’ secret tokens or share links. But in the affected versions, if you could run queries or trigger certain bugs, you might dump these values. With these tokens, you could access or download files meant to be private.

No complex skills needed! If someone can access the API or parts of the database, they can dump sensitive data.

Why Can’t Admins Just Fix It?

Unfortunately, even the Nextcloud admin panel could not solve the problem. Only direct changes to the database (risking data loss or corruption) might work. That’s why the official advice is: Upgrade Nextcloud!

1. Update Nextcloud

Upgrade to at least 23..9 or 24..5 (or any newer release). This fully patches the vulnerability.

- Nextcloud 23..9 Release Notes
- Nextcloud 24..5 Release Notes

Most hosting providers or community installers support one-click upgrades. If you self-host, follow the official update guide.

2. Monitor Server Logs

Look for unexplained data access, especially queries or logs involving the oc_share table or similar structures.

3. Revoke Old Shares

If you are worried that share tokens may have been leaked, revoke all old shared links. You can do this from the Nextcloud web UI or by asking users to re-share important files.

4. Regular Security Updates

Make it a habit to check for updates monthly or subscribe to Nextcloud’s security announcements.

Conclusion

CVE-2022-39329 highlighted that even mature projects like Nextcloud can suffer from tough, hard-to-patch vulnerabilities. If in doubt, always keep your software up-to-date—and if you’re a Nextcloud admin, double-check those version numbers!

Stay secure, and don’t let your cloud rain on your secrets.

References

- Official Advisory: nextcloud.com/security/advisory/?id=NC-SA-2022-034
- CVE Entry: nvd.nist.gov/vuln/detail/CVE-2022-39329
- GitHub Security Advisory: github.com/advisories/GHSA-v2w3-4g77-73h2
- Nextcloud Update Guide: docs.nextcloud.com

If you ever need help patching Nextcloud, reach out to the vibrant Nextcloud community!

Timeline

Published on: 10/27/2022 14:15:00 UTC
Last modified on: 10/31/2022 17:37:00 UTC