Kingcope discovered that the mod_sftp and mod_sftp_pam modules of proftpd, a powerful modular FTP/SFTP/FTPS server, are not properly validating input, before making pool allocations. An attacker can use this flaw to conduct denial of service attacks against the system running proftpd (resource exhaustion).
For the oldstable distribution (squeeze), this problem has been fixed in version 1.3.3a-6squeeze7.
For the stable distribution (wheezy), this problem has been fixed in version 1.3.4a-5+deb7u1.
For the testing (jessie) and unstable (sid) distributions, this problem will be fixed soon.
We recommend that you upgrade your proftpd-dfsg packages.