CVE-2025-65849
Summary
CVE-2025-65849 describes a critical cryptanalytic break in the Altcha Proof-of-Work obfuscation mode, affecting versions 0.8.0 and later. This vulnerability allows remote attackers to recover the Proof-of-Work nonce in constant time through mathematical deduction, potentially bypassing the intended bot mitigation measures. While the vendor disputes the severity, emphasizing the design goal of discouraging rather than preventing determined attackers, the CVSS score indicates a significant risk.
Technical Details
The vulnerability stems from a weakness in the mathematical obfuscation used by Altcha's Proof-of-Work mechanism. Specifically, the obfuscation applied to the nonce allows for a relatively straightforward mathematical inversion. An attacker can analyze the obfuscated data and, through a series of calculations, efficiently derive the original nonce value. This bypasses the intended computational cost associated with solving the Proof-of-Work, rendering it ineffective. The core issue lies in the predictability of the obfuscation algorithm, which doesn't provide sufficient cryptographic strength to withstand even basic cryptanalytic techniques. The vulnerability is present in the `helpers.ts` file of the Altcha repository, specifically within the obfuscation logic. A proof-of-concept exploit demonstrates the ease with which the nonce can be recovered.
Affected Products and Versions
- Any product utilizing Altcha Proof-of-Work obfuscation mode version 0.8.0 and later.
Since Altcha is a library integrated into various applications, the specific affected products are diverse and depend on the adoption of Altcha. It is crucial to assess whether your applications are using Altcha and, if so, which version.
Impact Assessment
Successful exploitation of this vulnerability allows attackers to bypass the intended bot mitigation measures provided by Altcha. This can lead to various negative consequences, depending on the context in which Altcha is used.
- Automated scraping and data harvesting
- Account creation abuse
- Denial-of-service attacks through automated requests
- Spam submissions
Remediation
Immediate Actions
- Evaluate Altcha Usage: Determine if your applications are using Altcha Proof-of-Work obfuscation mode version 0.8.0 or later.
- Monitor for Suspicious Activity: Closely monitor your systems for unusual traffic patterns or bot-like behavior.
Long-term Solutions
- Disable Obfuscation: If possible, disable the obfuscation mode in Altcha. This may reduce the effectiveness of the Proof-of-Work but eliminates the vulnerability.
- Implement Stronger Bot Mitigation: Consider implementing alternative or complementary bot mitigation techniques, such as CAPTCHAs, rate limiting, or behavioral analysis.
- Upgrade Altcha (If Available): Check for newer versions of Altcha that address this vulnerability. However, given the vendor's stance, a fix may not be forthcoming.
Detection & Scanning
Detecting this vulnerability requires analyzing the Altcha implementation in your applications and verifying if the Proof-of-Work obfuscation mode is enabled. You can also monitor network traffic for patterns indicative of nonce recovery attempts. A dedicated security scanner capable of analyzing JavaScript code and identifying vulnerable cryptographic implementations would be ideal.
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