CVE-2017-15270 in PSFTPd
Summary
by MITRE
The PSFTPd 10.0.4 Build 729 server does not properly escape data before writing it into a Comma Separated Values (CSV) file. This can be used by attackers to hide data in the Graphical User Interface (GUI) view and create arbitrary entries to a certain extent. Special characters such as '"' and ',' and '\r' are not escaped and can be used to add new entries to the log.
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Analysis
by VulDB Data Team • 01/10/2023
The vulnerability identified as CVE-2017-15270 affects PSFTPd version 10.0.4 Build 729, a file transfer protocol server implementation that generates CSV log files for tracking user activities and system operations. This security flaw represents a classic data injection vulnerability that occurs when the application fails to properly sanitize user input before incorporating it into structured data formats. The issue stems from inadequate input validation and output escaping mechanisms within the CSV file generation process, creating a vector for malicious data insertion that can compromise the integrity of the logging system.
The technical flaw manifests specifically in the CSV file writing functionality where special characters including double quotes, commas, and carriage return characters are not properly escaped or encoded before being written to log files. This omission allows attackers to manipulate the CSV structure by injecting these special characters in crafted user inputs or file names. When the CSV parser encounters these unescaped characters, it interprets them as structural elements rather than data content, enabling attackers to inject additional rows or columns into the log files. The vulnerability operates at the application layer and can be classified under CWE-15 as "External Control of System or Configuration Setting" and CWE-77 as "Command Injection" when considering the broader implications of data manipulation.
The operational impact of this vulnerability extends beyond simple data corruption, as it provides attackers with the ability to manipulate the GUI interface that displays these log files. By carefully crafting input data that contains unescaped CSV special characters, an attacker can create arbitrary entries in the log files that appear as legitimate system entries in the graphical interface. This manipulation can be used to hide malicious activities, create false audit trails, or potentially inject additional data that could confuse system administrators during forensic analysis. The vulnerability essentially allows for log poisoning attacks where the integrity of the audit trail is compromised, making it difficult to distinguish between legitimate and malicious activities within the system.
This vulnerability aligns with several ATT&CK techniques including T1070.004 "Indicator Removal on Host: File Deletion" through the potential for log manipulation and T1562.001 "Impair Defenses: Disable or Modify Tools" by compromising the logging infrastructure that security tools depend upon for monitoring. The vulnerability also represents a data integrity issue that can be exploited to undermine the trustworthiness of system logs, which are critical for security monitoring and incident response operations. Organizations relying on PSFTPd for file transfer operations face significant risk as this vulnerability can be exploited to create false records of user activities, potentially masking unauthorized access attempts or malicious file transfers.
Mitigation strategies should focus on implementing proper input sanitization and output escaping mechanisms within the CSV generation process. The application should escape special characters by wrapping fields containing commas or quotes with double quotes and by doubling any existing double quotes within the data. Additionally, implementing proper data validation at the point of input and ensuring that all user-supplied data is properly encoded before being written to structured files would prevent this vulnerability. Organizations should also consider implementing log file integrity monitoring solutions that can detect anomalies in CSV log structures and alert administrators to potential data manipulation attempts. Regular security updates and patches should be applied to ensure that the PSFTPd implementation remains protected against known vulnerabilities, and input validation should be strengthened to prevent similar issues in other data export functionalities.