stunnel 4.21 through 4.54, when CONNECT protocol negotiation and NTLM authentication are enabled, does not correctly perform integer conversion, which allows remote proxy servers to execute arbitrary code via a crafted request that triggers a buffer overflow.
https://www.stunnel.org/CVE-2013-1762.html
https://wiki.mageia.org/en/Support/Advisories/MGASA-2013-0097
http://www.mandriva.com/security/advisories?name=MDVSA-2013:130