CVE-2024-52510: Nextcloud Desktop Auth Bypass Vulnerability

CVE-2024-52510 Overview

CVE-2024-52510 affects the Nextcloud Desktop Client, the synchronization tool that connects user computers with a Nextcloud Server. The client failed to halt with an error when a manipulated server returned an empty initial signature. This behavior allowed attackers to bypass signature validation entirely. The flaw maps to [CWE-295] Improper Certificate Validation and impacts the integrity of file synchronization trust assumptions. Nextcloud addressed the issue in Desktop Client version 3.14.2.

Critical Impact
A malicious or compromised server can deliver unsigned or unverified content to the Desktop Client by sending an empty initial signature, defeating the signature validation mechanism that protects synchronized files.

Affected Products

Nextcloud Desktop Client versions prior to 3.14.2
Deployments synchronizing with untrusted or compromised Nextcloud servers
All platforms supported by the Nextcloud Desktop Client (Windows, macOS, Linux)

Discovery Timeline

2024-11-15 - CVE-2024-52510 published to the National Vulnerability Database
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2024-52510

Vulnerability Analysis

The Nextcloud Desktop Client validates signatures on data received from the configured Nextcloud Server to ensure file content integrity. The client logic did not treat an empty initial signature as a failure condition. Instead of aborting the operation and raising an error, the client continued execution, effectively bypassing the validation step. This breaks the trust boundary between the client and a potentially manipulated server, allowing unverified content to pass through the synchronization pipeline. The flaw is network-reachable and requires no authentication or user interaction to exploit.

Root Cause

The root cause is improper certificate or signature validation handling [CWE-295]. The client's signature verification routine accepted an empty signature value as a valid state rather than rejecting it. This is a classic missing-negative-case defect where absent cryptographic material should trigger a hard failure but is treated as benign. The GitHub commit 97539218e6f63c3a3fd1694cb7d8aef27c5910d7 and Pull Request #7333 introduce the corrected validation behavior.

Attack Vector

An attacker who controls or compromises a Nextcloud Server, or who can perform a man-in-the-middle position against the client-server channel, returns responses containing an empty initial signature field. The Desktop Client proceeds with synchronization without verifying authenticity. This allows the attacker to influence what the client trusts as legitimate server-supplied data, undermining the confidentiality guarantee the signature mechanism was meant to enforce. Technical details are documented in GitHub Security Advisory GHSA-r4qc-m9mj-452v and HackerOne Report #2597504.

Detection Methods for CVE-2024-52510

Indicators of Compromise

Nextcloud Desktop Client processes running versions older than 3.14.2 on managed endpoints
Outbound synchronization traffic to Nextcloud Server endpoints that are not under organizational control
Server responses with missing or empty signature fields in synchronization payloads

Detection Strategies

Inventory installed Nextcloud Desktop Client versions across the fleet and flag any instance below 3.14.2
Monitor TLS endpoints and certificate pinning logs for unexpected Nextcloud server hostnames or certificate changes
Alert on Desktop Client log entries that indicate signature validation events without corresponding non-empty signature values

Monitoring Recommendations

Track Nextcloud Desktop Client update telemetry through endpoint management tooling to confirm patched versions are deployed
Capture client-side error and synchronization logs centrally for retrospective analysis of signature handling
Watch for anomalous file changes propagated through Nextcloud sync directories that do not correlate with legitimate user activity

How to Mitigate CVE-2024-52510

Immediate Actions Required

Upgrade all Nextcloud Desktop Client installations to version 3.14.2 or later without delay
Audit the list of configured Nextcloud Server endpoints on each client and remove any that are not explicitly trusted
Validate that endpoint management tooling reports the corrected client version after rollout

Patch Information

The fix is delivered in Nextcloud Desktop Client 3.14.2. The corrective code change is published in GitHub commit 97539218e6f63c3a3fd1694cb7d8aef27c5910d7 and discussed in Pull Request #7333. The patch ensures that an empty initial signature is rejected and aborts the validation flow with an error.

Workarounds

Restrict Desktop Clients to synchronize only with Nextcloud Servers under direct administrative control until patches are applied
Enforce strict TLS configuration and certificate validation at the network layer to reduce man-in-the-middle exposure
Block outbound connections from Desktop Clients to untrusted Nextcloud hosts via host firewall or proxy policy

bash

# Verify installed Nextcloud Desktop Client version (Linux example)
nextcloud --version

# Expected output should report 3.14.2 or later