3proxy Stack Memory Disclosure via SOCKS4 Reply

Executive Summary

This vulnerability is an uninitialized stack memory disclosure flaw in 3proxy versions 0.9.7 through 1.0.1. When the external-NAT option (-Ne) is enabled, unauthenticated attackers can send a SOCKS4 probe that fails the version check. This triggers a reply containing uninitialized bytes from the sin structure, exposing high bytes of a userspace pointer and weakening ASLR protections.

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Detection Guidance

To detect this vulnerability, check if 3proxy is running with the external-NAT option (-Ne) enabled. Inspect logs for SOCKS4 protocol errors or unusual memory disclosures. Use network scanning tools to identify 3proxy instances and verify their versions against the affected range (0.9.7 to 1.0.1).

Commands: grep for '-Ne' in 3proxy config files, check version with '3proxy -v', and monitor for SOCKS4 reply anomalies in network traffic.

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Impact Analysis

An attacker could exploit this to leak sensitive memory addresses, reducing the effectiveness of ASLR which is a key security mechanism. This could aid in bypassing memory protections and facilitate further attacks like code execution or privilege escalation.

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Compliance Impact

This vulnerability exposes uninitialized stack memory, including high bytes of userspace pointers, which weakens ASLR protections. While not directly violating GDPR or HIPAA, such memory disclosure could potentially lead to information leaks that may compromise data confidentiality, a key requirement under both regulations.

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Mitigation Strategies

Immediately update 3proxy to a version beyond 1.0.1 or apply the fix from commit 206c923. Disable the external-NAT option (-Ne) if not required. Restrict access to SOCKS4 ports via firewall rules to limit exposure.

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