file/show.cgi in Webmin 1.590 and earlier allows remote authenticated users to execute arbitrary commands via an invalid character in a pathname, as demonstrated by a | (pipe) character.
americaninfosec.com/research/index.html
www.americaninfosec.com/research/dossiers/AISG-12-001.pdf
www.kb.cert.org/vuls/id/788478
www.securitytracker.com/id?1027507
www.xerox.com/download/security/security-bulletin/16287-4d6b7b0c81f7b/cert_XRX13-003_v1.0.pdf
github.com/webmin/webmin/commit/1f1411fe7404ec3ac03e803cfa7e01515e71a213