The RPC module in Webmin 0.21 through 0.99, when installed without root or admin privileges, allows remote attackers to read and write to arbitrary files and execute arbitrary commands via remote_foreign_require and remote_foreign_call requests.
Webmin before 0.5 does not restrict the number of invalid passwords that are entered for a valid username, which could allow remote attackers to gain privileges via brute force password cracking.