Stunnel Local Arbitrary Command Execution Vulnerability
Stunnel is an SSL encryption wrapper by Michal Trojnara. It is available for a number of platforms including FreeBSD, Debian Linux and RedHat Linux.
Insecurely-structured calls to syslog() found in certain versions of Stunnel (prior to version 3.9) pass user-supplied data to the syslog() function in such a way that maliciously embedded format specifiers in this data can cause the process to overwrite sections of its own memory with arbitrary data.
This user-supplied data is obtained from an identd server of a connecting host. If an attacker controls an ident server, an arbitrary username value containing malicious format specifiers can be sent to Stunnel.
This string would then be passed as part of the format string for the syslog() function, where the format specifiers would be interpreted.
This can lead to remote access being gained by the attacker on the target host with privileges of Stunnel, which can be required to run as root.