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# -*- coding: binary -*-
require 'msf/core/payload/uuid'
module Rex
module Payloads
module Meterpreter
module UriChecksum
#
# Define 8-bit checksums for matching URLs
# These are based on charset frequency
#
URI_CHECKSUM_INITW = 92 # Windows
URI_CHECKSUM_INITN = 92 # Native (same as Windows)
URI_CHECKSUM_INITP = 80 # Python
URI_CHECKSUM_INITJ = 88 # Java
URI_CHECKSUM_CONN = 98 # Existing session
URI_CHECKSUM_INIT_CONN = 95 # New stageless session
# Mapping between checksums and modes
URI_CHECKSUM_MODES = Hash[
URI_CHECKSUM_INITN, :init_native,
URI_CHECKSUM_INITP, :init_python,
URI_CHECKSUM_INITJ, :init_java,
URI_CHECKSUM_INIT_CONN, :init_connect,
URI_CHECKSUM_CONN, :connect
]
URI_CHECKSUM_MIN_LEN = 5
# Limit how long :connect URLs are to stay within 256 bytes when including
# the hostname, colon, port, and leading slash
URI_CHECKSUM_CONN_MAX_LEN = 128
URI_CHECKSUM_UUID_MIN_LEN = URI_CHECKSUM_MIN_LEN + Msf::Payload::UUID::UriLength
# Map "random" URIs to static strings, allowing us to randomize
# the URI sent in the first request.
#
# @param uri [String] The URI string from the HTTP request
# @return [Hash] The attributes extracted from the URI
def process_uri_resource(uri)
# Ignore non-base64url characters in the URL
uri_bare = uri.gsub(/[^a-zA-Z0-9_\-]/, '')
# Figure out the mode based on the checksum
uri_csum = Rex::Text.checksum8(uri_bare)
# Extract the UUID if the URI is long enough
uri_uuid = nil
if uri_bare.length >= URI_CHECKSUM_UUID_MIN_LEN
uri_uuid = Msf::Payload::UUID.new(uri: uri_bare)
end
uri_mode = URI_CHECKSUM_MODES[uri_csum]
# Return a hash of URI attributes
{ uri: uri_bare, sum: uri_csum, uuid: uri_uuid, mode: uri_mode }
end
# Create a URI that matches the specified checksum and payload uuid
#
# @param sum [Integer] A checksum mode value to use for the generated url
# @param uuid [Msf::Payload::UUID] A valid UUID object
# @param len [Integer] An optional URI length value, including the leading slash
# @return [String] The URI string for connections
def generate_uri_uuid(sum, uuid, len=nil)
curl_uri_len = URI_CHECKSUM_UUID_MIN_LEN + rand(URI_CHECKSUM_CONN_MAX_LEN - URI_CHECKSUM_UUID_MIN_LEN)
curl_prefix = uuid.to_uri
if len
# Subtract a byte to take into account the leading /
curl_uri_len = len - 1
end
if curl_uri_len < URI_CHECKSUM_UUID_MIN_LEN
raise ArgumentError, "Length must be #{URI_CHECKSUM_UUID_MIN_LEN+1} bytes or greater"
end
# Pad out the URI and make the checksum match the specified sum
"/" + generate_uri_checksum(sum, curl_uri_len, curl_prefix)
end
# Create an arbitrary length URI that matches a given checksum
#
# @param sum [Integer] The checksum value that the generated URI should match
# @param len [Integer] The length of the URI to generate
# @param prefix [String] The optional prefix to use to build the URI
# @return [String] The URI string that checksums to the given value
def generate_uri_checksum(sum, len=5, prefix="")
# Lengths shorter than 4 bytes are unable to match all possible checksums
# Lengths of exactly 4 are relatively slow to find for high checksum values
# Lengths of 5 or more bytes find a matching checksum fairly quickly (~80ms)
if len < URI_CHECKSUM_MIN_LEN
raise ArgumentError, "Length must be #{URI_CHECKSUM_MIN_LEN} bytes or greater"
end
gen_len = len-prefix.length
if gen_len < URI_CHECKSUM_MIN_LEN
raise ArgumentError, "Prefix must be at least {URI_CHECKSUM_MIN_LEN} bytes smaller than total length"
end
# Brute force a matching checksum for shorter URIs
if gen_len < 40
loop do
uri = prefix + Rex::Text.rand_text_base64url(gen_len)
return uri if Rex::Text.checksum8(uri) == sum
end
end
# The rand_text_base64url() method becomes a bottleneck at around 40 bytes
# Calculating a static prefix flattens out the average runtime for longer URIs
prefix << Rex::Text.rand_text_base64url(gen_len-20)
loop do
uri = prefix + Rex::Text.rand_text_base64url(20)
return uri if Rex::Text.checksum8(uri) == sum
end
end
# Return the numerical checksum for a given mode symbol
#
# @param mode [Symbol] The mode symbol to lookup (:connect, :init_native, :init_python, :init_java)
# @return [Integer] The URI checksum value corresponding with the mode
def uri_checksum_lookup(mode)
sum = URI_CHECKSUM_MODES.keys.select{|ksum| URI_CHECKSUM_MODES[ksum] == mode}.first
unless sum
raise ArgumentError, "Unknown checksum mode: #{mode}"
end
sum
end
end
end
end
end
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