CVE-2008-4500 in Serv-U
Summary
by MITRE
Serv-U 7.0.0.1 through 7.3, including 7.2.0.1, allows remote authenticated users to cause a denial of service (CPU consumption) via a crafted stou command, probably related to MS-DOS device names, as demonstrated using "con:1".
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Analysis
by VulDB Data Team • 11/06/2024
The vulnerability identified as CVE-2008-4500 affects Serv-U FTP server versions 7.0.0.1 through 7.3, including the specific 7.2.0.1 release, presenting a significant denial of service risk that can be exploited by authenticated remote attackers. This flaw specifically targets the handling of the stou command within the FTP protocol implementation, where the server fails to properly validate or sanitize input parameters that reference MS-DOS device names. The vulnerability manifests when a crafted stou command is issued with parameters referencing special device names such as "con:1", which are part of the legacy MS-DOS filesystem naming conventions. These device names represent special system resources that should be handled with extreme care in file system operations.
The technical exploitation of this vulnerability occurs through the improper processing of device name references within the stou command, which is typically used for storing files with unique names. When the server encounters a malformed stou command containing MS-DOS device names, the internal processing logic becomes trapped in a loop or consumes excessive CPU resources attempting to resolve or validate these special device references. This behavior creates a condition where legitimate system resources are consumed disproportionately, effectively rendering the FTP service unavailable to other users while the malicious command is being processed. The vulnerability's root cause aligns with CWE-20, which describes improper input validation, and specifically relates to CWE-129, concerning the improper validation of input boundaries, as the system fails to properly validate the boundaries of device name references in file operations.
The operational impact of this vulnerability extends beyond simple service disruption as it can be leveraged by malicious actors to consume system resources and potentially cause cascading failures in environments where multiple services depend on the affected FTP server. The CPU consumption pattern suggests that the vulnerability may trigger infinite loops or recursive processing within the server's command handling mechanism, where the system continuously attempts to process the invalid device name reference without proper termination conditions. This type of denial of service attack can be particularly damaging in enterprise environments where FTP services are critical for data transfer operations and where the availability of these services directly impacts business operations and user productivity. The vulnerability's exploitation requires only authenticated access to the FTP service, making it accessible to users who have valid credentials, which increases the risk profile significantly.
Mitigation strategies for CVE-2008-4500 should focus on implementing proper input validation and sanitization mechanisms within the FTP server's command processing pipeline. Organizations should apply the vendor-provided patches or updates that address the specific handling of device names in the stou command, ensuring that all MS-DOS special device names are properly rejected or handled with appropriate validation. Network segmentation and access control measures can provide additional protection by limiting the scope of potential exploitation, while monitoring systems should be deployed to detect unusual CPU consumption patterns that may indicate exploitation attempts. The vulnerability demonstrates the importance of considering legacy system compatibility issues when implementing modern security controls, as the MS-DOS device name handling represents a historical artifact that should not be permitted in modern file system operations. From an ATT&CK framework perspective, this vulnerability aligns with the T1499.004 technique for network denial of service and the T1566.001 technique for social engineering through credential access, as it requires legitimate authentication to exploit effectively.