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Miggo AIRoot Cause AnalysisThe vulnerability, CVE-2026-16599, describes a denial of service in GNU wget's FTP OPIE/S-KEY authentication functionality. The core issue is an unchecked iteration count for an MD5 key-derivation loop. A server-supplied sequence number is used directly as the loop's upper bound without any validation. This allows a malicious FTP server to force wget into an extremely long computation, effectively causing a denial of service.
Despite attempts to retrieve the specific commit details from both GitLab and a constructed GitHub URL, direct access to the patch content was not possible. Therefore, the identification of the vulnerable function relies on the detailed description provided in the CVE and CERT Polska advisory.
The description explicitly points to an 'MD5 key-derivation loop' where the 'server-supplied sequence number' is used as an 'iteration count without any upper bound validation'. This indicates that the function responsible for handling the OPIE/S-KEY challenge, parsing the sequence number, and then executing the MD5 loop is the vulnerable component. While the exact function name and file path cannot be confirmed without the patch, a function named ftp_opie_skey_md5_loop (or similar, such as skey_md5_challenge or opie_authenticate_challenge) within a file like lib/ftp-opie.c is a highly probable candidate based on common naming conventions for such functionality in C projects like wget. This function would be directly involved in processing the malicious input (the large sequence number) and performing the unbounded computation.
Exploitation would involve an attacker setting up a malicious FTP server or intercepting FTP traffic to send a crafted OPIE challenge with a sequence number close to INT_MAX. When wget attempts to authenticate, it would call this function, which would then enter an extremely long MD5 computation loop, consuming significant CPU resources and leading to a denial of service for the client.
ftp_opie_skey_md5_looplib/ftp-opie.c