CVE-2024-52510

What it actually does

The client accepts an empty initial signature from a manipulated server instead of terminating the connection, allowing the signature validation step to be skipped entirely.

Why it matters to the business

Organizations using the affected client risk silent acceptance of tampered file metadata or content during synchronization, undermining data integrity and potentially enabling supply-chain style attacks on shared files.

How an attack unfolds

An attacker positions a malicious or compromised Nextcloud server instance that responds to the desktop client's initial signature request with an empty value; the client proceeds without error instead of aborting, permitting subsequent unsigned or forged responses to be processed.

How to fix it

Upgrade Nextcloud Desktop client to version 3.14.2 or later; the fix is present in commit 5b9cebb4aba3548101cace9080ea1f98d244d0b3. Verify installed version and enforce client updates via organizational distribution mechanisms.

How to confirm the fix worked

Confirm client version is 3.14.2 or newer; test by pointing a client at a server that deliberately returns an empty signature and verify the connection is rejected.

Typical attack path

1. Attacker deploys or compromises a server that mimics a legitimate Nextcloud instance
2. Victim desktop client connects and requests signature material
3. Server returns an empty initial signature
4. Client bypasses validation and continues the sync session
5. Attacker supplies altered file lists, metadata, or content that the client accepts

How to detect it

Inspect desktop client logs for signature validation entries that lack an error when the server supplied no signature; correlate with connections to non-standard server addresses or unexpected sync activity.

What your security team should do

• Prioritize upgrade of all Nextcloud Desktop clients to 3.14.2+ within the next patch cycle
• Monitor vendor release channels for backported fixes in supported older branches
• Review synchronization logs for connections to unexpected server endpoints
• Educate users on verifying server certificates and avoiding untrusted instances