Denial of Service in Tor Network via Compression Bomb Bypass

Executive Summary

Tor before 0.4.9.9 is vulnerable to a compression bomb bypass. An attacker can bypass the compression bomb check by concatenating many gzip or zlib sub-streams, each just under the detection threshold. This allows the attacker to avoid triggering the compression bomb protection entirely.

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Detection Guidance

This vulnerability involves a compression bomb bypass in Tor versions before 0.4.9.9. Detection requires checking Tor version and monitoring for unusual network traffic patterns. Use 'tor --version' to verify the installed version. If the version is below 0.4.9.9, the system is vulnerable. Additionally, inspect network traffic for excessive gzip or zlib compression streams, which may indicate an attempt to exploit this issue.

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Impact Analysis

This vulnerability could allow an attacker to send large amounts of compressed data to a Tor relay or client without triggering the compression bomb protection. This may lead to denial-of-service conditions by consuming excessive memory or CPU resources on the affected system.

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Compliance Impact

This vulnerability does not directly affect compliance with GDPR or HIPAA as it relates to a compression bomb bypass in Tor software. However, if exploited, it could lead to denial-of-service conditions, potentially impacting availability of systems handling sensitive data, which may indirectly affect compliance with availability requirements in regulations like HIPAA.

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Mitigation Strategies

Update Tor to version 0.4.9.9 or later to address the compression bomb bypass vulnerability. Monitor network traffic for unusual patterns that may indicate attempts to exploit this issue.

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