Medium [CVE-2026-58469] Memory corruption via crafted Metalink URL

GNU Wget through 1.25.0, fixed in commit 37a40fc, contains a heap buffer underread vulnerability in the clean_metalink_string() function within src/metalink.c that allows a malicious server to trigger memory corruption by serving a Metalink document containing a whitespace-only URL.

Attackers can cause the function to decrement a pointer past the start of the buffer when processing an all-whitespace Metalink URL, potentially leading to abnormal program behavior. This could lead to memory corruption and abnormal program behavior, potentially causing a denial of service.

Moderate: A heap-buffer-underread in GNU Wget's clean_metalink_string() function, affecting Red Hat Enterprise Linux 8, can be triggered when wget processes a specially crafted Metalink document containing a resource URL consisting only of whitespace characters.

This code path is only reachable when Wget's Metalink support is explicitly requested via --input-metalink or --metalink-over-http; it is not exercised during ordinary downloads. Successful exploitation requires a user to invoke Wget's Metalink handling against an attacker-controlled or compromised server.

The out-of-bounds byte is read only to decide whether to continue a trim loop and is never returned, logged, or written -- the practical impact is limited to a crash of the wget process (denial of service), not memory corruption or code execution.