CVE-2021-32689 – This vulnerability in Nextcloud Talk allows use... (How to Fix)

Q: What is the severity of CVE-2021-32689?

CVE-2021-32689 has a CVSS score of 8.1 (HIGH). This vulnerability in Nextcloud Talk allows user impersonation through username reuse, enabling unauthorized access to chat messages. Attackers who can register with a previously used username can read all messages sent to the original user. This affects all Nextcloud Talk instances with versions before 11.2.2 where user-provided usernames are permitted.

📋 TL;DR

This vulnerability in Nextcloud Talk allows user impersonation through username reuse, enabling unauthorized access to chat messages. Attackers who can register with a previously used username can read all messages sent to the original user. This affects all Nextcloud Talk instances with versions before 11.2.2 where user-provided usernames are permitted.

💻 Affected Systems

Products:

Nextcloud Talk

Versions: All versions prior to 11.2.2

Operating Systems: All platforms running Nextcloud Talk

Default Config Vulnerable: ✅ No

Notes: Only vulnerable when user providers allow users to choose their own usernames, which is not the default Nextcloud behavior.

📦 What is this software?

Talk by Nextcloud

View all CVEs affecting Talk →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete compromise of private chat communications, including sensitive business discussions, personal conversations, and potentially credential disclosure.

🟠

Likely Case

Unauthorized access to chat histories, leading to information disclosure, privacy violations, and potential blackmail or social engineering opportunities.

🟢

If Mitigated

Minimal impact if username reuse is prevented and proper access controls are enforced.

🌐 Internet-Facing: HIGH - Any internet-facing Nextcloud Talk instance with vulnerable configuration is exposed to username enumeration and reuse attacks.

🏢 Internal Only: MEDIUM - Internal attackers with user registration capabilities could exploit this, but external attack surface is reduced.

🎯 Exploit Status

Public PoC: ⚠️ Yes

Weaponized: LIKELY

Unauthenticated Exploit: ✅ No

Complexity: LOW

Exploitation requires ability to register with a previously used username. The HackerOne report demonstrates the attack vector clearly.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: 11.2.2 or 11.3.0

Vendor Advisory: https://github.com/nextcloud/security-advisories/security/advisories/GHSA-xv6f-344w-895c

Restart Required: Yes

Instructions:

1. Backup your Nextcloud instance. 2. Update Nextcloud Talk to version 11.2.2 or higher via the Nextcloud app store or manual installation. 3. Restart the web server and any relevant services. 4. Verify the update was successful.

🔧 Temporary Workarounds

Disable user-chosen usernames

all

Prevent users from selecting their own usernames, forcing system-generated unique identifiers

Configure user provider to disallow custom usernames (implementation varies by provider)

🧯 If You Can't Patch

Disable user registration entirely if not required
Implement monitoring for username reuse attempts and investigate any occurrences

🔍 How to Verify

Check if Vulnerable:

Check Nextcloud Talk version via Nextcloud admin interface or by examining the app directory version file

Check Version:

Check Nextcloud admin panel -> Apps -> Installed apps -> Nextcloud Talk version

Verify Fix Applied:

Confirm version is 11.2.2 or higher and test that username reuse no longer grants access to previous user's messages

📡 Detection & Monitoring

Log Indicators:

Multiple user registrations with similar usernames
Failed login attempts followed by successful registration with similar username
Unusual access patterns to chat history

Network Indicators:

Rapid user registration attempts
Patterns of username enumeration

SIEM Query:

source="nextcloud.log" AND ("user registration" OR "username") AND ("duplicate" OR "reuse" OR "already exists")

📊 Metadata

CVE ID: CVE-2021-32689

CVSS v3 Score: 8.1 (HIGH)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

CWE: CWE-200

Published: July 12, 2021

Last Updated: November 21, 2024

🔗 References

https://github.com/nextcloud/security-advisories/security/advisories/GHSA-xv6f-344w-895c Third Party Advisory
https://github.com/nextcloud/spreed/pull/5633 Patch,Third Party Advisory
https://github.com/nextcloud/spreed/releases/tag/v11.2.2 Release Notes,Third Party Advisory
https://github.com/nextcloud/spreed/releases/tag/v11.3.0 Release Notes,Third Party Advisory
https://hackerone.com/reports/1200700 Permissions Required
https://github.com/nextcloud/security-advisories/security/advisories/GHSA-xv6f-344w-895c Third Party Advisory
https://github.com/nextcloud/spreed/pull/5633 Patch,Third Party Advisory
https://github.com/nextcloud/spreed/releases/tag/v11.2.2 Release Notes,Third Party Advisory
https://github.com/nextcloud/spreed/releases/tag/v11.3.0 Release Notes,Third Party Advisory
https://hackerone.com/reports/1200700 Permissions Required

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