GNU ed before 0.2-18.1 allows local users to overwrite the files of other users via a symlink attack.
https://exchange.xforce.ibmcloud.com/vulnerabilities/5723
http://www.redhat.com/support/errata/RHSA-2000-123.html
http://www.linux-mandrake.com/en/security/MDKSA-2000-076.php3
http://www.debian.org/security/2000/20001129
http://distro.conectiva.com.br/atualizacoes/?id=a&anuncio=000359