nfqsed is a command line utility that transparently modifies network traffic using a predefined set of substitution rules. It runs on Linux and uses the netfilter_queue library. It is similar to netsed but it also allows modifying the network traffic passing through an ethernet bridge. This is especially useful in situations where the source MAC address needs to stay unchanged.

Usage

Usage: nfqsed -s /val1/val2 [-s /val1/val2] [-f file] [-v] [-q num]
  -s /val1/val2    - replaces occurences of val1 with val2 in the packet payload
                     except the '?' character in val1 matches any byte
  -f file          - read replacement rules from the specified file
  -q num           - bind to queue with number 'num' (default 0)
  -v               - be verbose, can be specified up to 4 times for extra info

Example

Replace occurrences of foo with bar and occurrences of good with evil in all forwarded packets that have destination port 554:

# iptables -A FORWARD -p tcp --destination-port 554 -j NFQUEUE --queue-num 0
# nfqsed -s /foo/bar -s /good/evil

TODO

• different lengths of val1 and val2
• binary rules