wget OPIE Auth DoS via Unbounded MD5 Loop
CVE-2026-16599 Published on August 25, 2026
Denial of Service in GNU wget
GNU wget is vulnerable to denial of service in its FTP OPIE/S-KEY authentication functionality. The server-supplied sequence number from the FTP challenge line is used as an iteration count for an MD5 key-derivation loop without any upper bound validation. A malicious FTP server or a network attacker positioned to intercept FTP traffic can send a crafted OPIE challenge with a sequence number near INT_MAX, causing wget to perform up to approximately 2.1 billion MD5 computations and suspend for some time. The --timeout option does not mitigate this because it applies only to network I/O, not CPU computation.
This issue was fixed in commit e9697d98e7249b0f68a6be040a4f3dcc5bc101fa
Vulnerability Analysis
CVE-2026-16599 can be exploited with network access. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity and availability.
Weakness Type
Unchecked Input for Loop Condition
The product does not properly check inputs that are used for loop conditions, potentially leading to a denial of service or other consequences because of excessive looping.
Products Associated with CVE-2026-16599
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Affected Versions
GNU wget:- Before and including 1.25.0 is affected.