mirror of https://github.com/OISF/suricata
You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
65 lines
2.5 KiB
ReStructuredText
65 lines
2.5 KiB
ReStructuredText
Base64 keywords
|
|
===============
|
|
|
|
Suricata supports decoding base64 encoded data from buffers and matching on the decoded data.
|
|
|
|
This is achieved by using two keywords, ``base64_decode`` and ``base64_data``. Both keywords must be used in order to generate an alert.
|
|
|
|
base64_decode
|
|
-------------
|
|
|
|
Decodes base64 data from a buffer and makes it available for the base64_data function.
|
|
|
|
Syntax::
|
|
|
|
base64_decode:bytes <value>, offset <value>, relative;
|
|
|
|
The ``bytes`` option specifies how many bytes Suricata should decode and make available for base64_data.
|
|
The decoding will stop at the end of the buffer.
|
|
|
|
The ``offset`` option specifies how many bytes Suricata should skip before decoding.
|
|
Bytes are skipped relative to the start of the payload buffer if the ``relative`` is not set.
|
|
|
|
The ``relative`` option makes the decoding start relative to the previous content match. Default behavior is to start at the beginning of the buffer.
|
|
This option makes ``offset`` skip bytes relative to the previous match.
|
|
|
|
.. note:: Regarding ``relative`` and ``base64_decode``:
|
|
|
|
The content match that you want to decode relative to must be the first match in the stream.
|
|
|
|
.. note:: ``base64_decode`` follows RFC 4648 by default i.e. encounter with any character that is not found in the base64 alphabet leads to rejection of that character and the rest of the string.
|
|
|
|
See Redmine Bug 5223: https://redmine.openinfosecfoundation.org/issues/5223 and RFC 4648: https://www.rfc-editor.org/rfc/rfc4648#section-3.3
|
|
|
|
base64_data
|
|
-----------
|
|
|
|
base64_data is a ``sticky buffer``.
|
|
|
|
Enables content matching on the data previously decoded by base64_decode.
|
|
|
|
Example
|
|
-------
|
|
|
|
Here is an example of a rule matching on the base64 encoded string "test" that is found inside the http_uri buffer.
|
|
|
|
It starts decoding relative to the known string "somestring" with the known offset of 1. This must be the first occurrence of "somestring" in the buffer.
|
|
|
|
Example::
|
|
|
|
Buffer content:
|
|
http_uri = "GET /en/somestring&dGVzdAo=¬_base64"
|
|
|
|
Rule:
|
|
alert http any any -> any any (msg:"Example"; http.uri; content:"somestring"; \
|
|
base64_decode:bytes 8, offset 1, relative; \
|
|
base64_data; content:"test"; sid:10001; rev:1;)
|
|
|
|
Buffer content:
|
|
http_uri = "GET /en/somestring&dGVzdAo=¬_base64"
|
|
|
|
Rule:
|
|
alert http any any -> any any (msg:"Example"; content:"somestring"; http_uri; \
|
|
base64_decode:bytes 8, offset 1, relative; \
|
|
base64_data; content:"test"; sid:10001; rev:1;)
|