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Sentry: Bruteforce Attack Blocker

sentry - safe and effective protection against bruteforce attacks. It detects and prevents bruteforce attacks against sshd using minimal system resources.

SAFE

To prevent inadvertant lockouts, Sentry auto-whitelists IPs that have connected more than 3 times and succeeded at least once. Now that forgetful colleague behind the office NAT router won't get us locked out of our system. Again. Nor the admin whose script just failed to login 12 times in 2 seconds.

Sentry includes support for adding IPs to a firewall. Support for IPFW, PF, ipchains is included. Firewall support is disabled by default. Firewall rules may terminate existing session(s) to the host (attn. IPFW users). Get your IPs whitelisted (connect 3x or use --whitelist) before enabling the firewall option.

SIMPLE

Sentry is written in perl, which is installed nearly everywhere you find sshd. It has no dependencies. Installation and deployment is extremely simple.

FLEXIBLE

Sentry supports blocking connection attempts using tcpwrappers and several popular firewalls. It is easy to extend sentry to support additional blocking lists.

Sentry was written to protect the SSH daemon but also blocks on FTP and MUA logs. As this was written, the primary attack platform in use is bot nets comprised of exploited PCs on high-speed internet connections. These bots are used for carrying out SSH attacks as well as spam delivery. Blocking bots prevents multiple attack vectors.
The programming style of sentry makes it easy to insert code for additonal functionality.

EFFICIENT

The primary goal of Sentry is to minimize the resources an attacker can steal, while consuming minimal resources itself. Most bruteforce blocking apps (denyhosts, fail2ban, sshdfilter) expect to run as a daemon, tailing a log file. That requires a language interpreter to always be running, consuming at least 10MB of RAM. A single hardware node with dozens of virtual servers will lose hundreds of megs to daemon protection. Sentry uses resources only when connections are made.

Once an IP is blacklisted for abuse, whether by tcpd or a firewall, the resources it can consume are practically zero.


IP REPORT

$ /var/db/sentry/sentry.pl -r --ip=24.19.45.95
   9 connections from 24.19.45.95
       and it is whitelisted

HOME GATEWAY REPORT

$ /var/db/sentry/sentry.pl -r
  -------- summary ---------
  1614 unique IPs have connected 76525 times
  1044 IPs are blacklisted
    18 IPs are whitelisted

WEB SERVER REPORT

$ /var/db/sentry/sentry.pl -r
 -------- summary ---------
 1240 unique IPs have connected 285554 times
   40 IPs are blacklisted
    4 IPs are whitelisted

EUROPEAN DNS MIRROR

$ /var/db/sentry/sentry.pl -r
-------- summary ---------
3484 unique IPs have connected 15391 times
1127 IPs are blacklisted
   6 IPs are whitelisted

Download and read more at
Sentry: Bruteforce Attack Blocker Reviewed by Ethical Hacking on 8:42 AM Rating: 5

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