16.2. Lua functions¶
16.2.1. Differences between output and detect:¶
Currently, the needs key initialization varies, depending on what is the goal of the script: output or detection.
If the script is for detection, the needs initialization should be as seen in the example below (see Lua Scripting for Detection for a complete example of a detection script):
function init (args)
local needs = {}
needs["packet"] = tostring(true)
return needs
end
For output logs, follow the pattern below. (The complete script structure can be seen at Lua Output:)
function init (args)
local needs = {}
needs["protocol"] = "http"
return needs
end
Do notice that the functions and protocols available for log and match may also vary. DNP3, for instance, is not
available for logging.
16.2.2. packet¶
Initialize with:
function init (args)
local needs = {}
needs["type"] = "packet"
return needs
end
16.2.2.1. 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
16.2.2.2. SCPacketTimeString¶
Use SCPacketTimeString to get the packet's time string in the format:
11/24/2009-18:57:25.179869
function log(args)
ts = SCPacketTimeString()
16.2.2.3. SCPacketTuple¶
ipver, srcip, dstip, proto, sp, dp = SCPacketTuple()
16.2.2.4. SCPacketPayload¶
p = SCPacketPayload()
16.2.3. flow¶
function init (args)
local needs = {}
needs["type"] = "flow"
return needs
end
16.2.3.1. 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()
16.2.3.2. SCFlowTimeString¶
startts = SCFlowTimeString()
16.2.3.3. SCFlowTuple¶
ipver, srcip, dstip, proto, sp, dp = SCFlowTuple()
16.2.3.4. SCFlowAppLayerProto¶
Get alproto as a 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".
16.2.3.5. SCFlowHasAlerts¶
Returns true if flow has alerts.
Example:
function log(args)
has_alerts = SCFlowHasAlerts()
if has_alerts then
-- do something
end
end
16.2.3.6. SCFlowStats¶
Gets the packet and byte counts per flow.
tscnt, tsbytes, tccnt, tcbytes = SCFlowStats()
16.2.3.7. 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")
16.2.4. http¶
For output, init with:
function init (args)
local needs = {}
needs["protocol"] = "http"
return needs
end
For detection, use the specific buffer (cf Lua Scripting for Detection for a complete list), as with:
function init (args)
local needs = {}
needs["http.uri"] = tostring(true)
return needs
end
16.2.4.1. 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 available.
Example:
function log(args)
a, o, e = HttpGetResponseBody();
--print("offset " .. o .. " end " .. e)
for n, v in ipairs(a) do
print(v)
end
end
16.2.4.2. 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
16.2.4.3. HttpGetRequestHeader¶
http_ua = HttpGetRequestHeader("User-Agent")
if http_ua == nil then
http_ua = "<useragent unknown>"
end
16.2.4.4. HttpGetResponseHeader¶
server = HttpGetResponseHeader("Server");
print ("Server: " .. server);
16.2.4.5. HttpGetRequestLine¶
rl = HttpGetRequestLine();
print ("Request Line: " .. rl);
16.2.4.6. HttpGetResponseLine¶
rsl = HttpGetResponseLine();
print ("Response Line: " .. rsl);
16.2.4.7. HttpGetRawRequestHeaders¶
rh = HttpGetRawRequestHeaders();
print ("Raw Request Headers: " .. rh);
16.2.4.8. HttpGetRawResponseHeaders¶
rh = HttpGetRawResponseHeaders();
print ("Raw Response Headers: " .. rh);
16.2.4.9. HttpGetRequestUriRaw¶
http_uri = HttpGetRequestUriRaw()
if http_uri == nil then
http_uri = "<unknown>"
end
16.2.4.10. HttpGetRequestUriNormalized¶
http_uri = HttpGetRequestUriNormalized()
if http_uri == nil then
http_uri = "<unknown>"
end
16.2.4.11. HttpGetRequestHeaders¶
a = HttpGetRequestHeaders();
for n, v in pairs(a) do
print(n,v)
end
16.2.4.12. HttpGetResponseHeaders¶
a = HttpGetResponseHeaders();
for n, v in pairs(a) do
print(n,v)
end
16.2.5. DNS¶
If your purpose is to create a logging script, initialize the buffer as:
function init (args)
local needs = {}
needs["protocol"] = "dns"
return needs
end
If you are going to use the script for rule matching, choose one of the available DNS buffers listed in Lua Scripting for Detection and follow the pattern:
function init (args)
local needs = {}
needs["dns.rrname"] = tostring(true)
return needs
end
16.2.5.1. 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
16.2.5.2. 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
16.2.5.3. 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
16.2.5.4. DnsGetRcode¶
rcode = DnsGetRcode();
if rcode == nil then
return 0
end
print (rcode)
returns a lua string with the error message, or nil
16.2.5.5. DnsGetRecursionDesired¶
if DnsGetRecursionDesired() == true then
print ("RECURSION DESIRED")
end
returns a bool
16.2.6. TLS¶
For log output, initialize with:
function init (args)
local needs = {}
needs["protocol"] = "tls"
return needs
end
For detection, initialization is as follows:
function init (args)
local needs = {}
needs["tls"] = tostring(true)
return needs
end
16.2.6.1. TlsGetVersion¶
Get the negotiated version in a TLS session as a string through TlsGetVersion.
Example:
function log (args)
version = TlsGetVersion()
if version then
-- do something
end
end
16.2.6.2. 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
16.2.6.3. 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
16.2.6.4. 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
16.2.6.5. 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
16.2.6.6. TlsGetCertSerial¶
Get TLS certificate serial number through TlsGetCertSerial.
Example:
function log (args)
serial = TlsGetCertSerial()
if serial then
-- do something
end
end
16.2.6.7. 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 something
end
end
16.2.7. JA3¶
JA3 must be enabled in the Suricata config file (set 'app-layer.protocols.tls.ja3-fingerprints' to 'yes').
For log output, initialize with:
function init (args)
local needs = {}
needs["protocol"] = "tls"
return needs
end
For detection, initialization is as follows:
function init (args)
local needs = {}
needs["tls"] = tostring(true)
return needs
end
16.2.7.1. Ja3GetHash¶
Get the JA3 hash (md5sum of JA3 string) through Ja3GetHash.
Example:
function log (args)
hash = Ja3GetHash()
if hash == nil then
return
end
end
16.2.7.2. Ja3GetString¶
Get the JA3 string through Ja3GetString.
Example:
function log (args)
str = Ja3GetString()
if str == nil then
return
end
end
16.2.7.3. Ja3SGetHash¶
Get the JA3S hash (md5sum of JA3S string) through JA3SGetHash.
Examples:
function log (args)
hash = Ja3SGetHash()
if hash == nil then
return
end
end
Or, for detection:
function match (args)
hash = Ja3SGetHash()
if hash == nil then
return 0
end
// matching code
return 0
end
16.2.7.4. JA3SGetString¶
Get the JA3S string through Ja3SGetString.
Examples:
function log (args)
str = Ja3SGetString()
if str == nil then
return
end
end
Or, for detection:
function match (args)
str = Ja3SGetString()
if str == nil then
return 0
end
// matching code
return 0
end
16.2.8. SSH¶
Initialize with:
function init (args)
local needs = {}
needs["protocol"] = "ssh"
return needs
end
16.2.8.1. 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
16.2.8.2. SshGetServerSoftwareVersion¶
Get SSH software used by the server through SshGetServerSoftwareVersion.
Example:
function log (args)
software = SshGetServerSoftwareVersion()
if software == nil then
return 0
end
end
16.2.8.3. 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
16.2.8.4. SshGetClientSoftwareVersion¶
Get SSH software used by the client through SshGetClientSoftwareVersion.
Example:
function log (args)
software = SshGetClientSoftwareVersion()
if software == nil then
return 0
end
end
16.2.8.5. HasshGet¶
Get MD5 of hassh algorithms used by the client through HasshGet.
Example:
function log (args)
hassh = HasshGet()
if hassh == nil then
return 0
end
end
16.2.8.6. HasshGetString¶
Get hassh algorithms used by the client through HasshGetString.
Example:
function log (args)
hassh_string = HasshGetString()
if hassh == nil then
return 0
end
end
16.2.8.7. HasshServerGet¶
Get MD5 of hassh algorithms used by the server through HasshServerGet.
Example:
function log (args)
hassh_string = HasshServerGet()
if hassh == nil then
return 0
end
end
16.2.8.8. HasshServerGetString¶
Get hassh algorithms used by the server through HasshServerGetString.
Example:
function log (args)
hassh_string = HasshServerGetString()
if hassh == nil then
return 0
end
end
16.2.9. 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
16.2.9.1. SCFileInfo¶
fileid, txid, name, size, magic, md5, sha1, sha256 = SCFileInfo()
returns fileid (number), txid (number), name (string), size (number), magic (string), md5 in hex (string), sha1 (string), sha256 (string)
16.2.10. Alerts¶
Alerts are a subset of the 'packet' logger:
function init (args)
local needs = {}
needs["type"] = "packet"
needs["filter"] = "alerts"
return needs
end
16.2.10.1. SCRuleIds¶
sid, rev, gid = SCRuleIds()
16.2.10.3. SCRuleMsg¶
msg = SCRuleMsg()
16.2.10.4. SCRuleClass¶
class, prio = SCRuleClass()
16.2.11. 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
16.2.11.1. SCStreamingBuffer¶
function log(args)
data = SCStreamingBuffer()
hex_dump(data)
end
16.2.12. 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 dedicated 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
16.2.12.1. SCFlowintGet¶
Get the Flowint at index given by the parameter.
16.2.12.2. SCFlowintSet¶
Set the Flowint at index given by the first parameter. The second parameter is the value.
16.2.12.3. SCFlowintIncr¶
Increment Flowint at index given by the first parameter.
16.2.12.4. SCFlowintDecr¶
Decrement Flowint at index given by the first parameter.
16.2.12.5. SCFlowvarGet¶
Get the Flowvar at index given by the parameter.
16.2.12.6. 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
16.2.13. Misc¶
16.2.13.1. SCThreadInfo¶
tid, tname, tgroup = SCThreadInfo()
It gives: tid (integer), tname (string), tgroup (string)
16.2.13.2. 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")
16.2.13.3. SCLogPath¶
Expose the log path.
name = "fast_lua.log"
function setup (args)
filename = SCLogPath() .. "/" .. name
file = assert(io.open(filename, "a"))
end
16.2.13.4. SCByteVarGet¶
Get the ByteVar at index given by the parameter. These variables are defined by byte_extract or byte_math in Suricata rules. Only callable from match scripts.
function init(args)
local needs = {}
needs["bytevar"] = {"var1", "var2"}
return needs
end
Here we define a register that we will be using variables var1 and var2. The access to the Byte variables is done by index.
function match(args)
var1 = SCByteVarGet(0)
var2 = SCByteVarGet(1)