CVE-2025-65849
📋 TL;DR
A cryptanalytic vulnerability in Altcha's Proof-of-Work obfuscation mode allows attackers to recover the nonce in constant time, bypassing the intended bot/scraping protection. This affects websites using Altcha version 0.8.0+ with obfuscation mode enabled. The vendor disputes this as a vulnerability since the mechanism is designed for discouraging bots, not resisting determined attackers.
💻 Affected Systems
- Altcha Proof-of-Work obfuscation mode
⚠️ Manual Verification Required
This CVE does not have specific version information in our database, so automatic vulnerability detection cannot determine if your system is affected.
Why? The CVE database entry doesn't specify which versions are vulnerable (no version ranges provided by the vendor/NVD).
🔒 Custom verification scripts are available for registered users. Sign up free to download automated test scripts.
- Review the CVE details at NVD
- Check vendor security advisories for your specific version
- Test if the vulnerability is exploitable in your environment
- Consider updating to the latest version as a precaution
⚠️ Risk & Real-World Impact
Worst Case
Attackers bypass all bot/scraping protection, allowing automated data extraction at scale without computational cost.
Likely Case
Automated bots bypass the Proof-of-Work mechanism, defeating the primary anti-scraping protection.
If Mitigated
Limited impact if alternative bot detection methods are in place, but the specific Proof-of-Work protection is ineffective.
🎯 Exploit Status
Public proof-of-concept code exists (altcha-deobfs repository), making exploitation straightforward for attackers with basic programming skills.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: N/A
Vendor Advisory: N/A
Restart Required: No
Instructions:
No official patch available as vendor disputes this as a vulnerability. Consider alternative bot protection mechanisms.
🔧 Temporary Workarounds
Disable Obfuscation Mode
allSwitch from obfuscation mode to standard Altcha mode which doesn't use the vulnerable Proof-of-Work implementation.
Modify Altcha configuration to remove obfuscation mode settings
🧯 If You Can't Patch
- Implement additional bot detection layers (rate limiting, behavioral analysis, CAPTCHA)
- Monitor for unusual scraping patterns and implement WAF rules to block suspicious traffic
🔍 How to Verify
Check if Vulnerable:
Check if using Altcha version 0.8.0+ with obfuscation mode enabled in configuration.Check Version:
Check package.json or Altcha configuration for version numberVerify Fix Applied:
Verify obfuscation mode is disabled or alternative bot protection is implemented.📡 Detection & Monitoring
Log Indicators:
- Unusual volume of successful form submissions bypassing Proof-of-Work
- Consistent pattern of requests completing Proof-of-Work in constant time
Network Indicators:
- High volume of automated requests from single IPs
- Requests completing Proof-of-Work challenges suspiciously quickly
SIEM Query:
source="web_logs" AND (message="Altcha verification" OR message="Proof-of-Work") AND status="success" | stats count by ip | where count > threshold