kcope has reported a vulnerability in Linux-ftpd-ssl, which can be exploited by malicious users to compromise a vulnerable system.
The vulnerability is caused due to the unsafe use of the "vsprintf()" function in the FTP server to generate replies in response to commands received from the FTP client. This causes a stack-based buffer overflow when the output of a command exceeds 2048 bytes. The vulnerability can be exploited by creating multiple levels of sub-directories with long names, and then issuing the "XPWD" command when at the lowest level sub-directory. The resulting path name that is generated in response the "XPWD" will exceed 2048 bytes, overflowing the stack-buffer.
Successful exploitation requires that the user is able to create directories on the FTP server, or perform some actions that will cause the FTP server to generate an overly long reply.
The vulnerability affects NetKit Linux-ftpd version 0.17 with the Linux-ftpd-ssl patch version 0.3. Other versions may also be vulnerable.
NOTE: The vulnerability was introduced due to the Linux-ftpd-ssl patch. An exploit for this vulnerability is publicly available.
Solution: Grant only trusted users access to the FTP server.
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Subject: Linux-ftpd-ssl FTP Server Response Buffer Overflow Vulnerability
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