A stack-based buffer overflow vulnerability exists in the md4sum() function of libsoup’s NTLM authentication module (SoupAuthNTLM). When NTLM authentication is enabled, insufficient bounds checking on stack-allocated buffers can allow a local attacker to overwrite adjacent memory. This may result in arbitrary code execution with the privileges of the affected application. Multiple widely deployed components, including WebKit, Evolution, GVfs, and gnome-online-accounts, enable NTLM by default, increasing exposure.