CVE-2020-36946: SyncBreeze DoS Vulnerability

CVE-2020-36946 Overview

CVE-2020-36946 is a denial of service vulnerability affecting SyncBreeze version 10.0.28. The vulnerability exists in the login endpoint and allows remote attackers to crash the service by sending an oversized payload in the login request. This resource exhaustion attack can overwhelm the application and disrupt service availability for legitimate users.

Critical Impact

Remote unauthenticated attackers can crash the SyncBreeze service, causing complete denial of service and potential business disruption for organizations relying on file synchronization capabilities.

Affected Products

• SyncBreeze version 10.0.28
• SyncBreeze Enterprise (affected versions)
• SyncBreeze Pro (affected versions)

Discovery Timeline

• 2026-01-27 - CVE-2020-36946 published to NVD
• 2026-01-29 - Last updated in NVD database

Technical Details for CVE-2020-36946

Vulnerability Analysis

This vulnerability is classified under CWE-770 (Allocation of Resources Without Limits or Throttling). The root cause lies in the application's failure to properly validate and limit the size of input data received through the login endpoint. When an attacker sends an excessively large payload to the authentication mechanism, the application attempts to process it without adequate bounds checking, leading to resource exhaustion and service crash.

The network-based attack vector allows remote exploitation without requiring authentication or user interaction, making this vulnerability particularly dangerous for internet-exposed SyncBreeze installations. The impact is limited to availability, with no direct effect on confidentiality or integrity of data.

Root Cause

The vulnerability stems from improper input validation in the login request handler. The application fails to implement adequate resource allocation limits when processing authentication requests, allowing attackers to submit payloads that exceed expected boundaries. This lack of input size validation and resource throttling enables the denial of service condition.

Attack Vector

The attack exploits the network-accessible login endpoint of SyncBreeze. An attacker can craft a malicious HTTP request containing an oversized payload directed at the authentication mechanism. When the application attempts to process this abnormally large request, it exhausts available resources and crashes, denying service to legitimate users.

The attack requires no authentication and can be executed remotely over the network. Technical details and proof-of-concept information are available through the Exploit-DB #49291 entry.

Detection Methods for CVE-2020-36946

Indicators of Compromise

• Abnormally large HTTP POST requests targeting the SyncBreeze login endpoint
• Sudden service crashes or restarts of the SyncBreeze process
• Network traffic patterns showing repeated large payload submissions to authentication URLs
• System logs indicating resource exhaustion or memory allocation failures

Detection Strategies

• Monitor HTTP request sizes to the SyncBreeze web interface for anomalous payload lengths
• Implement network-level intrusion detection rules to flag oversized authentication requests
• Configure application-level logging to capture and alert on login endpoint anomalies
• Deploy SentinelOne Singularity to detect and prevent exploitation attempts targeting the SyncBreeze service

Monitoring Recommendations

• Enable detailed logging for the SyncBreeze web server component
• Set up alerts for service availability and unexpected process terminations
• Monitor network traffic for patterns consistent with DoS attack attempts
• Implement baseline monitoring for normal request sizes to the login endpoint

How to Mitigate CVE-2020-36946

Immediate Actions Required

• Restrict network access to the SyncBreeze web interface using firewall rules
• Implement web application firewall (WAF) rules to limit request payload sizes
• Consider disabling the web interface if not required for operations
• Monitor for exploitation attempts using available detection strategies

Patch Information

Consult the SyncBreeze Official Site for the latest version and security updates. Organizations should upgrade to a patched version as soon as one becomes available. Review the VulnCheck Advisory for additional remediation guidance.

Workarounds

• Implement request size limits at the network perimeter or reverse proxy level
• Restrict access to the SyncBreeze web interface to trusted IP addresses only
• Deploy a reverse proxy with request body size limits in front of the SyncBreeze service
• Consider isolating the SyncBreeze service on a segmented network to limit exposure

# Example: Configure nginx as reverse proxy with request size limits
# Add to nginx server configuration for SyncBreeze
client_max_body_size 1m;
client_body_buffer_size 16k;
limit_req_zone $binary_remote_addr zone=login:10m rate=10r/s;

# Apply rate limiting to login endpoint
location /login {
    limit_req zone=login burst=5 nodelay;
    proxy_pass http://syncbreeze-backend;
}