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The vulnerability (CVE-2025-XXXX) in Meteor (up to v3.2.1) arises from inefficient regular expression (regex) complexity in the `Object.assign` function within packages/ddp-server/livedata_server.js. The issue occurs when processing the `forwardedFor` argument, leading to potential ReDoS (Regular Expression Denial of Service) attacks. Attackers can exploit this by crafting a malicious `forwardedFor` header with a specially designed string that triggers catastrophic backtracking in the regex engine. This causes excessive CPU consumption, degrading server performance or causing denial of service.
The attack is remote but complex, requiring precise input manipulation. Meteor patched this in v3.2.2 by optimizing the regex pattern to avoid exponential time complexity.
DailyCVE Form:
Platform: Meteor
Version: <= 3.2.1
Vulnerability: ReDoS
Severity: Moderate
Date: May 16, 2025
What Undercode Say:
Exploitation:
- Craft a malicious HTTP request with a `forwardedFor` header containing a regex-heavy string:
GET / HTTP/1.1 Host: target.com X-Forwarded-For: aaaaaaaaaaaaaaaaaaaaaaaaaaaa!
- Use automated tools (e.g.,
curl, Burp Suite) to send repeated requests:while true; do curl -H "X-Forwarded-For: aaaaaaaaaaa!" http://target.com; done
Protection:
1. Patch Immediately:
meteor update --release 3.2.2
2. Input Sanitization:
function sanitizeForwardedFor(header) {
return header.replace(/[^\d.,\s]/g, '');
}
3. Rate Limiting:
import { DDPRateLimiter } from 'meteor/ddp-rate-limiter';
DDPRateLimiter.addRule({ type: 'method' }, 5, 1000);
Detection:
1. Check server logs for abnormal CPU spikes:
grep -i "X-Forwarded-For" /var/log/meteor.log | awk '{print $1}' | uniq -c
2. Monitor regex execution time:
console.time("regexTest");
/^(?:[0-9]{1,3}.){3}[0-9]{1,3}$/.test(maliciousInput);
console.timeEnd("regexTest");
Mitigation Workarounds:
- Use a reverse proxy (Nginx) to filter malicious headers:
location / { if ($http_x_forwarded_for ~ "(\s|\,|$)") { return 403; } } - Implement WAF rules to block suspicious patterns.
References:
Sources:
Reported By: github.com
Extra Source Hub:
Undercode
