CVE-2015-7665 in Talis
Summary
by MITRE
Tails before 1.7 includes the wget program but does not prevent automatic fallback from passive FTP to active FTP, which allows remote FTP servers to discover the Tor client IP address by reading a (1) PORT or (2) EPRT command. NOTE: within wget itself, the automatic fallback is not considered a vulnerability by CVE.
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Analysis
by VulDB Data Team • 07/01/2022
The vulnerability described in CVE-2015-7665 affects the Tails operating system version 1.7 and earlier, specifically addressing a security flaw in how the wget network utility handles FTP connections. This issue arises from wget's default behavior of automatically falling back from passive FTP mode to active FTP mode when passive mode fails or is not supported by the remote server. The Tails distribution, designed specifically for privacy and anonymity, includes wget as part of its standard toolset, but fails to properly configure or disable this automatic fallback mechanism that poses significant risks to user anonymity when connecting through the Tor network.
The technical flaw stems from the fundamental difference between passive and active FTP modes and how they handle IP address information. In passive FTP, the server provides a port number for the client to connect to, while active FTP requires the server to connect back to the client's IP address and port. When wget automatically switches from passive to active mode, it sends a PORT or EPRT command to the FTP server, which then uses the client's IP address as specified in these commands. This creates a direct information leak where remote FTP servers can discover the true IP address of the Tor client, effectively breaking the anonymity that Tails aims to provide. The vulnerability is particularly dangerous because it operates transparently without user intervention, making it difficult to detect or prevent.
The operational impact of this vulnerability is severe for users relying on Tails for anonymity and privacy protection. When users connect to FTP servers through Tails, their real IP address becomes discoverable by the FTP servers they interact with, potentially exposing their location and identity. This information leak undermines the entire purpose of using Tails with Tor, as it defeats the fundamental anonymity protections that users expect. The vulnerability affects all users of Tails versions prior to 1.7, making it a widespread issue that could compromise the security of individuals who depend on Tails for sensitive activities requiring anonymity. This flaw particularly impacts users who must access FTP servers or those who are unaware of the potential information leakage, creating an unexpected risk to their privacy.
The mitigation for this vulnerability involves configuring wget to disable automatic fallback to active FTP mode or upgrading to Tails version 1.7 or later where this issue has been addressed. System administrators and security professionals should ensure that wget is configured with appropriate FTP settings that prevent automatic mode switching, typically by setting specific parameters that force passive FTP usage exclusively. This aligns with the principle of least privilege and defense in depth as outlined in cybersecurity best practices. The vulnerability can be classified under CWE-200 (Information Exposure) and relates to the broader category of anonymity and privacy breaches in network communications. From an ATT&CK framework perspective, this vulnerability maps to T1071.004 (Application Layer Protocol: DNS) and T1566 (Phishing) as it enables adversaries to gain information about network infrastructure and user locations, potentially facilitating more sophisticated targeting attacks. Organizations should also consider implementing network monitoring to detect unusual FTP traffic patterns that might indicate this vulnerability being exploited, as well as ensuring that all network utilities are properly configured to maintain anonymity requirements.