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Sniffpass will alert on cleartext passwords discovered in HTTP POST requests.

By default it will not log passwords, but only log the username in a post_username field in http.log and create an entry in notice.log that a password was observed.


  • Install via Zeek package manager:

     $ zkg install zeek-sniffpass
     # or for legacy installs
     $ bro-pkg install zeek-sniffpass
  • Download the files to $PREFIX/bro/share/bro/site/sniffpass and add the following to your local.bro:
      @load ./sniffpass


  • You can enable different types of password logging. Add one (or more) of the following options to your local.bro file:
      redef SNIFFPASS::log_password_plaintext = T;
      redef SNIFFPASS::log_password_md5 = T;
      redef SNIFFPASS::log_password_sha1 = T;
      redef SNIFFPASS::log_password_sha256 = T;
  • You can disable logging to notice.log using this flag:

      redef SNIFFPASS::notice_log_enable = F;
  • By default, only the first 300 bytes of an HTTP POST request are parsed. This can be changed by adding the following to your local.bro file and setting your own value:

      redef SNIFFPASS::post_body_limit = 300

Broker Support

Zeek can use Broker to publish discovered username and passwords. This can be useful in cases where credentials shouldn't be saved to disk in a Zeek log file, but instead have them handled by a script. One use case of this is sending them to an API to retire valid credentials seen.

  • Broker publishing is disabled by default, but can be enabled using this flag:
      redef SNIFFPASS::broker_enable = T;
      redef SNIFFPASS::broker_host = 9999/tcp;
      redef SNIFFPASS::broker_port = "";
  • You can change the topic to something other than the default:

      redef SNIFFPASS::broker_topic = "/sniffpass/credentials_seen";

    Example Broker Python Script

    This example was borrowed from the Broker documentation

    import broker import sys

    # Setup endpoint and connect to Zeek. ep = broker.Endpoint() sub = ep.make_subscriber("/sniffpass/credentials_seen") ss = ep.make_status_subscriber(True); ep.peer("", 9999)

    # Wait until connection is established. st = ss.get()

    if not (type(st) == broker.Status and st.code() == broker.SC.PeerAdded):

      print("could not connect")

    while True:

      (t, d) = sub.get()
      event = broker.zeek.Event(d)
      print("received {}{}".format(event.name(), event.args()))

Will give output like this when plaintext credentials are seen:

$ python test_broker.py
received SNIFFPASS::credentials_seen[u'my_username', u'Thi1sI$myP@ssw0rd']

Detailed Broker Output

There is an option to also include Destination IP, Destination Port, and full URL in the Broker output.

You can enable a more detailed output in Broker:

redef SNIFFPASS::broker_detailed = T;

The output from the Example Python Script:

$ python test_broker.py
received SNIFFPASS::credentials_seen_detailed[(u'my_username', u'Thi1sI$myP@ssw)rd'), IPv4Address(u''), 80/tcp, u'localhost/']

Automated Testing

Automated tests are done against the http_post.trace file with Travis CI.


  • If you are having any issues, ensure that you have TCP Checksumming disabled in your local.bro file, as per Zeek Documentation

      redef ignore_checksums = T;

Created By

Andrew Klaus (Cybera)

This module was inspired by the University of Alberta's 2019 CUCCIO Innovation Award Plaintext Password Sniffing Project.

Package Version :