chfn (change finger information) is one of the utilities in
the util-linux package.
The BindView RAZOR Team has discovered a local root vulnerability
in chfn which is described in the Bindview Advisory.
Under certain conditions, "a
carefully crafted attack sequence can be performed to exploit a
complex file locking and modification race present in this utility,
and, as a result, alter /etc/passwd to escalate privileges in the
system." The conditions include a password file, /etc/passwd, over 4 kilobytes and locating the attacker's account record in any
but the last 4 kB chunk of the file.
CERT/CC Vulnerability Note VU#405955 util-linux package vulnerable to privilege escalation when "ptmptmp" file is not removed properly when using "chfn" utility
