CVE-2024-52805
📋 TL;DR
Synapse Matrix homeserver versions before 1.120.1 have a vulnerability where multipart/form-data requests can cause excessive memory consumption in certain configurations. This can be exploited to amplify denial of service attacks against the server. All Synapse instances with default or custom configurations accepting multipart/form-data are affected.
💻 Affected Systems
- Synapse (Matrix homeserver)
📦 What is this software?
Synapse by Matrix
⚠️ Risk & Real-World Impact
Worst Case
Complete service outage due to memory exhaustion, causing the Synapse server to crash or become unresponsive, potentially affecting all Matrix users on that homeserver.
Likely Case
Degraded performance and intermittent service disruptions as memory consumption spikes during request processing, impacting user experience and server reliability.
If Mitigated
Minimal impact with proper rate limiting, memory monitoring, and request filtering in place, though some performance degradation may still occur during attack attempts.
🎯 Exploit Status
Exploitation requires sending specially crafted multipart/form-data requests. No authentication needed, making it accessible to any network-accessible attacker.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 1.120.1
Vendor Advisory: https://github.com/element-hq/synapse/security/advisories/GHSA-rfq8-j7rh-8hf2
Restart Required: Yes
Instructions:
1. Backup your Synapse configuration and database. 2. Update Synapse using pip: 'pip install --upgrade matrix-synapse==1.120.1'. 3. Restart the Synapse service: 'systemctl restart synapse.service' or equivalent. 4. Verify the update with 'synapse --version'.
🔧 Temporary Workarounds
Block multipart/form-data requests
allConfigure reverse proxy or firewall to reject requests with Content-Type: multipart/form-data before they reach Synapse.
# Example nginx configuration:
location / {
if ($http_content_type ~* "multipart/form-data") {
return 444;
}
proxy_pass http://synapse:8008;
}
Implement rate limiting
allConfigure aggressive rate limiting on multipart/form-data endpoints to reduce attack impact.
# Example using nginx limit_req:
limit_req_zone $binary_remote_addr zone=multipart:10m rate=1r/s;
location /_matrix/client/r0/upload {
limit_req zone=multipart burst=5 nodelay;
proxy_pass http://synapse:8008;
}
🧯 If You Can't Patch
- Deploy a WAF or reverse proxy with strict request size limits and multipart/form-data filtering
- Implement comprehensive monitoring and alerting for memory usage spikes with automated restart procedures
🔍 How to Verify
Check if Vulnerable:
Check Synapse version with 'synapse --version' or examine package version. If version is below 1.120.1, system is vulnerable.Check Version:
synapse --versionVerify Fix Applied:
After updating, verify with 'synapse --version' shows 1.120.1 or higher. Test by sending a multipart/form-data request - it should be rejected with appropriate error.📡 Detection & Monitoring
Log Indicators:
- Spike in memory usage logs
- Multiple requests with Content-Type: multipart/form-data in access logs
- Error logs showing multipart processing failures or memory allocation errors
Network Indicators:
- Unusually large number of POST requests with multipart/form-data content type
- Requests with abnormally large Content-Length headers
- Traffic patterns showing repeated upload attempts
SIEM Query:
source="synapse.log" AND ("multipart/form-data" OR "memory allocation" OR "out of memory") | stats count by src_ip