CVE-2009-4775 in WS_FTP
Summary
by MITRE
Format string vulnerability in Ipswitch WS_FTP Professional 12 before 12.2 allows remote attackers to cause a denial of service (crash) via format string specifiers in the status code portion of an HTTP response.
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Analysis
by VulDB Data Team • 02/03/2025
The vulnerability identified as CVE-2009-4775 represents a critical format string flaw within Ipswitch WS_FTP Professional version 12.0 and earlier, specifically affecting the software's handling of HTTP response status codes. This vulnerability falls under the category of improper input validation and demonstrates how insufficient sanitization of user-supplied data can lead to severe operational disruptions. The flaw exists in the application's HTTP response processing mechanism where it fails to properly validate or escape format string specifiers that may be present in the status code portion of incoming HTTP responses. This weakness creates an exploitable condition that remote attackers can leverage to manipulate the application's behavior through carefully crafted malicious input.
The technical execution of this vulnerability involves the exploitation of format string vulnerabilities that occur when an application uses user-controllable input directly in formatting functions without proper validation or sanitization. In this specific case, the WS_FTP Professional client processes HTTP responses and passes status code information through formatting functions that do not properly handle format specifiers. When an attacker crafts an HTTP response containing malicious format string specifiers within the status code field, the application's parsing routine interprets these specifiers as formatting instructions rather than literal text. This misinterpretation causes the application to attempt to read from arbitrary memory locations or execute invalid operations, leading to application instability and eventual crash. The vulnerability is classified as a CWE-134, which specifically addresses the use of format strings with user-supplied data without proper validation, making it a direct implementation of the well-known format string attack pattern.
The operational impact of this vulnerability extends beyond simple denial of service conditions, as it can potentially lead to complete application termination and service disruption for legitimate users. When the application crashes due to malformed format string processing, it affects the FTP client's ability to establish or maintain connections, effectively preventing file transfer operations. This type of vulnerability is particularly dangerous in enterprise environments where automated FTP processes rely on stable client functionality, as it can cause cascading failures in data transfer workflows and system integration processes. The vulnerability also aligns with ATT&CK technique T1499.004, which involves network disruption through application or service denial of service, as the exploitation directly targets the application's core functionality to create operational disruptions.
Mitigation strategies for CVE-2009-4775 primarily focus on updating to the patched version of Ipswitch WS_FTP Professional 12.2 or later, which addresses the format string vulnerability through proper input validation and sanitization. Organizations should implement network-level controls to monitor and filter HTTP responses that may contain suspicious format string patterns, though this approach provides only partial protection. The vulnerability demonstrates the importance of input validation and proper error handling in client applications, particularly those that process network data from untrusted sources. Security teams should also consider implementing network segmentation and access controls to limit exposure to potentially malicious HTTP responses that could be used to exploit this vulnerability. Additionally, regular security assessments of client applications should include testing for format string vulnerabilities, as they represent a common class of flaws that can be exploited to cause significant operational impact. The remediation process should also involve comprehensive testing to ensure that the patched version maintains all necessary functionality while eliminating the vulnerability.