14.2. Lua functions

14.2.1. packet

Initialize with:

function init (args)
    local needs = {}
    needs["type"] = "packet"
    return needs
end

14.2.1.1. SCPacketTimestamp

Get packets timestamp as 2 numbers: seconds & microseconds elapsed since 1970-01-01 00:00:00 UTC.

function log(args)
    local sec, usec = SCPacketTimestamp()
end

14.2.1.2. SCPacketTimeString

Add SCPacketTimeString to get the packets time string in the format: 11/24/2009-18:57:25.179869

function log(args)
    ts = SCPacketTimeString()

14.2.1.3. SCPacketTuple

ipver, srcip, dstip, proto, sp, dp = SCPacketTuple()

14.2.1.4. SCPacketPayload

p = SCPacketPayload()

14.2.2. flow

function init (args)
    local needs = {}
    needs["type"] = "flow"
    return needs
end

14.2.2.1. SCFlowTimestamps

Get timestamps (seconds and microseconds) of the first and the last packet from the flow.

startts, lastts = SCFlowTimestamps()
startts_s, lastts_s, startts_us, lastts_us = SCFlowTimestamps()

14.2.2.2. SCFlowTimeString

startts = SCFlowTimeString()

14.2.2.3. SCFlowTuple

ipver, srcip, dstip, proto, sp, dp = SCFlowTuple()

14.2.2.4. SCFlowAppLayerProto

Get alprotos as string from the flow. If a alproto is not (yet) known, it returns “unknown”.

Example:

function log(args)
    alproto = SCFlowAppLayerProto()
    if alproto ~= nil then
        print (alproto)
    end
end

Returns 5 values: <alproto> <alproto_ts> <alproto_tc> <alproto_orig> <alproto_expect>

Orig and expect are used when changing and upgrading protocols. In a SMTP STARTTLS case, orig would normally be set to “smtp” and expect to “tls”.

14.2.2.5. SCFlowHasAlerts

Returns true if flow has alerts.

Example:

function log(args)
    has_alerts = SCFlowHasAlerts()
    if has_alerts then
        -- do something
    end
end

14.2.2.6. SCFlowStats

Gets the packet and byte counts per flow.

tscnt, tsbytes, tccnt, tcbytes = SCFlowStats()

14.2.2.7. SCFlowId

Gets the flow id.

id = SCFlowId()

Note that simply printing ‘id’ will likely result in printing a scientific notation. To avoid that, simply do:

id = SCFlowId()
idstr = string.format("%.0f",id)
print ("Flow ID: " .. idstr .. "\n")

14.2.3. http

Init with:

function init (args)
    local needs = {}
    needs["protocol"] = "http"
    return needs
end

14.2.3.1. HttpGetRequestBody and HttpGetResponseBody.

Make normalized body data available to the script through HttpGetRequestBody and HttpGetResponseBody.

There no guarantees that all of the body will be availble.

Example:

function log(args)
    a, o, e = HttpGetResponseBody();
    --print("offset " .. o .. " end " .. e)
    for n, v in ipairs(a) do
        print(v)
    end
end

14.2.3.2. HttpGetRequestHost

Get the host from libhtp’s tx->request_hostname, which can either be the host portion of the url or the host portion of the Host header.

Example:

http_host = HttpGetRequestHost()
if http_host == nil then
    http_host = "<hostname unknown>"
end

14.2.3.3. HttpGetRequestHeader

http_ua = HttpGetRequestHeader("User-Agent")
if http_ua == nil then
    http_ua = "<useragent unknown>"
end

14.2.3.4. HttpGetResponseHeader

server = HttpGetResponseHeader("Server");
print ("Server: " .. server);

14.2.3.5. HttpGetRequestLine

rl = HttpGetRequestLine();
print ("Request Line: " .. rl);

14.2.3.6. HttpGetResponseLine

rsl = HttpGetResponseLine();
print ("Response Line: " .. rsl);

14.2.3.7. HttpGetRawRequestHeaders

rh = HttpGetRawRequestHeaders();
print ("Raw Request Headers: " .. rh);

14.2.3.8. HttpGetRawResponseHeaders

rh = HttpGetRawResponseHeaders();
print ("Raw Response Headers: " .. rh);

14.2.3.9. HttpGetRequestUriRaw

http_uri = HttpGetRequestUriRaw()
if http_uri == nil then
    http_uri = "<unknown>"
end

14.2.3.10. HttpGetRequestUriNormalized

http_uri = HttpGetRequestUriNormalized()
if http_uri == nil then
    http_uri = "<unknown>"
end

14.2.3.11. HttpGetRequestHeaders

a = HttpGetRequestHeaders();
for n, v in pairs(a) do
    print(n,v)
end

14.2.3.12. HttpGetResponseHeaders

a = HttpGetResponseHeaders();
for n, v in pairs(a) do
    print(n,v)
end

14.2.4. DNS

14.2.4.1. DnsGetQueries

dns_query = DnsGetQueries();
if dns_query ~= nil then
    for n, t in pairs(dns_query) do
        rrname = t["rrname"]
        rrtype = t["type"]

        print ("QUERY: " .. ts .. " " .. rrname .. " [**] " .. rrtype .. " [**] " ..
               "TODO" .. " [**] " .. srcip .. ":" .. sp .. " -> " ..
               dstip .. ":" .. dp)
    end
end

returns a table of tables

14.2.4.2. DnsGetAnswers

dns_answers = DnsGetAnswers();
if dns_answers ~= nil then
    for n, t in pairs(dns_answers) do
        rrname = t["rrname"]
        rrtype = t["type"]
        ttl = t["ttl"]

        print ("ANSWER: " .. ts .. " " .. rrname .. " [**] " .. rrtype .. " [**] " ..
               ttl .. " [**] " .. srcip .. ":" .. sp .. " -> " ..
               dstip .. ":" .. dp)
    end
end

returns a table of tables

14.2.4.3. DnsGetAuthorities

dns_auth = DnsGetAuthorities();
if dns_auth ~= nil then
    for n, t in pairs(dns_auth) do
        rrname = t["rrname"]
        rrtype = t["type"]
        ttl = t["ttl"]

        print ("AUTHORITY: " .. ts .. " " .. rrname .. " [**] " .. rrtype .. " [**] " ..
               ttl .. " [**] " .. srcip .. ":" .. sp .. " -> " ..
               dstip .. ":" .. dp)
    end
end

returns a table of tables

14.2.4.4. DnsGetRcode

rcode = DnsGetRcode();
if rcode == nil then
    return 0
end
print (rcode)

returns a lua string with the error message, or nil

14.2.4.5. DnsGetRecursionDesired

if DnsGetRecursionDesired() == true then
    print ("RECURSION DESIRED")
end

returns a bool

14.2.5. TLS

Initialize with:

function init (args)
    local needs = {}
    needs["protocol"] = "tls"
    return needs
end

14.2.5.1. TlsGetCertInfo

Make certificate information available to the script through TlsGetCertInfo.

Example:

function log (args)
    version, subject, issuer, fingerprint = TlsGetCertInfo()
    if version == nil then
        return 0
    end
end

14.2.5.2. TlsGetCertChain

Make certificate chain available to the script through TlsGetCertChain.

The output is an array of certificate with each certificate being an hash with data and length keys.

Example:

-- Use debian lua-luaossl coming from https://github.com/wahern/luaossl
local x509 = require"openssl.x509"

   chain = TlsGetCertChain()
   for k, v in pairs(chain) do
      -- v.length is length of data
      -- v.data is raw binary data of certificate
      cert = x509.new(v["data"], "DER")
      print(cert:text() .. "\n")
   end

14.2.5.3. TlsGetCertNotAfter

Get the Unix timestamp of end of validity of certificate.

Example:

function log (args)
    notafter = TlsGetCertNotAfter()
    if notafter < os.time() then
        -- expired certificate
    end
end

14.2.5.4. TlsGetCertNotBefore

Get the Unix timestamp of beginning of validity of certificate.

Example:

function log (args)
    notbefore = TlsGetCertNotBefore()
    if notbefore > os.time() then
        -- not yet valid certificate
    end
end

14.2.5.5. TlsGetCertSerial

Get TLS certificate serial number through TlsGetCertSerial.

Example:

function log (args)
    serial = TlsGetCertSerial()
    if serial then
        -- do something
    end
end

14.2.5.6. TlsGetSNI

Get the Server name Indication from a TLS connection.

Example:

function log (args)
    asked_domain = TlsGetSNI()
    if string.find(asked_domain, "badguys") then
        -- ok connection to bad guys let's do someting
    end
end

14.2.6. JA3

JA3 must be enabled in the Suricata config file (set ‘app-layer.protocols.tls.ja3-fingerprints’ to ‘yes’).

Initialize with:

function init (args)
    local needs = {}
    needs["protocol"] = "tls"
    return needs
end

14.2.6.1. Ja3GetHash

Get the JA3 hash (md5sum of JA3 string) through Ja3GetHash.

Example:

function log (args)
    hash = Ja3GetHash()
    if hash == nil then
        return
    end
end

14.2.6.2. Ja3GetString

Get the JA3 string through Ja3GetString.

Example:

function log (args)
    str = Ja3GetString()
    if str == nil then
        return
    end
end

14.2.7. SSH

Initialize with:

function init (args)
    local needs = {}
    needs["protocol"] = "ssh"
    return needs
end

14.2.7.1. SshGetServerProtoVersion

Get SSH protocol version used by the server through SshGetServerProtoVersion.

Example:

function log (args)
    version = SshGetServerProtoVersion()
    if version == nil then
        return 0
    end
end

14.2.7.2. SshGetServerSoftwareVersion

Get SSH software used by the server through SshGetServerSoftwareVersion.

Example:

function log (args)
    software = SshGetServerSoftwareVersion()
    if software == nil then
        return 0
    end
end

14.2.7.3. SshGetClientProtoVersion

Get SSH protocol version used by the client through SshGetClientProtoVersion.

Example:

function log (args)
    version = SshGetClientProtoVersion()
    if version == nil then
        return 0
    end
end

14.2.7.4. SshGetClientSoftwareVersion

Get SSH software used by the client through SshGetClientSoftwareVersion.

Example:

function log (args)
    software = SshGetClientSoftwareVersion()
    if software == nil then
        return 0
    end
end

14.2.8. Files

To use the file logging API, the script’s init() function needs to look like:

function init (args)
    local needs = {}
    needs['type'] = 'file'
    return needs
end

14.2.8.1. SCFileInfo

fileid, txid, name, size, magic, md5 = SCFileInfo()

returns fileid (number), txid (number), name (string), size (number), magic (string), md5 in hex (string)

14.2.8.2. SCFileState

state, stored = SCFileState()

returns state (string), stored (bool)

14.2.9. Alerts

Alerts are a subset of the ‘packet’ logger:

function init (args)
    local needs = {}
    needs["type"] = "packet"
    needs["filter"] = "alerts"
    return needs
end

14.2.9.1. SCRuleIds

sid, rev, gid = SCRuleIds()

14.2.9.2. SCRuleMsg

msg = SCRuleMsg()

14.2.9.3. SCRuleClass

class, prio = SCRuleClass()

14.2.10. Streaming Data

Streaming data can currently log out reassembled TCP data and normalized HTTP data. The script will be invoked for each consecutive data chunk.

In case of TCP reassembled data, all possible overlaps are removed according to the host OS settings.

function init (args)
    local needs = {}
    needs["type"] = "streaming"
    needs["filter"] = "tcp"
    return needs
end

In case of HTTP body data, the bodies are unzipped and dechunked if applicable.

function init (args)
    local needs = {}
    needs["type"] = "streaming"
    needs["protocol"] = "http"
    return needs
end

14.2.10.1. SCStreamingBuffer

function log(args)
    data = SCStreamingBuffer()
    hex_dump(data)
end

14.2.11. Flow variables

It is possible to access, define and modify Flow variables from Lua. To do so, you must use the functions described in this section and declare the counter in init function:

function init(args)
    local needs = {}
    needs["tls"] tostring(true)
    needs["flowint"] = {"tls-cnt"}
    return needs
end

Here we define a tls-cnt Flowint that can now be used in output or in a signature via dedicted functions. The access to the Flow variable is done by index so in our case we need to use 0.

function match(args)
    a = ScFlowintGet(0);
    if a then
        ScFlowintSet(0, a + 1)
    else
        ScFlowintSet(0, 1)
    end

14.2.11.1. ScFlowintGet

Get the Flowint at index given by the parameter.

14.2.11.2. ScFlowintSet

Set the Flowint at index given by the first parameter. The second parameter is the value.

14.2.11.3. ScFlowintIncr

Increment Flowint at index given by the first parameter.

14.2.11.4. ScFlowintDecr

Decrement Flowint at index given by the first parameter.

14.2.11.5. ScFlowvarGet

Get the Flowvar at index given by the parameter.

14.2.11.6. ScFlowvarSet

Set a Flowvar. First parameter is the index, second is the data and third is the length of data.

You can use it to set string

function init (args)
    local needs = {}
    needs["http.request_headers"] = tostring(true)
    needs["flowvar"] = {"cnt"}
    return needs
end

function match(args)
    a = ScFlowvarGet(0);
    if a then
        a = tostring(tonumber(a)+1)
        ScFlowvarSet(0, a, #a)
    else
        a = tostring(1)
        ScFlowvarSet(0, a, #a)
    end

14.2.12. Misc

14.2.12.1. SCThreadInfo

tid, tname, tgroup = SCThreadInfo()

It gives: tid (integer), tname (string), tgroup (string)

14.2.12.2. SCLogError, SCLogWarning, SCLogNotice, SCLogInfo, SCLogDebug

Print a message. It will go into the outputs defined in the yaml. Whether it will be printed depends on the log level.

Example:

SCLogError("some error message")

14.2.12.3. SCLogPath

Expose the log path.

name = "fast_lua.log"
function setup (args)
    filename = SCLogPath() .. "/" .. name
    file = assert(io.open(filename, "a"))
end