/usr/share/bro/policy/misc/scan.bro is in bro-common 2.5-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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# ..Authors: Sheharbano Khattak
# Seth Hall
# All the authors of the old scan.bro
@load base/frameworks/notice
@load base/frameworks/sumstats
@load base/utils/time
module Scan;
export {
redef enum Notice::Type += {
## Address scans detect that a host appears to be scanning some
## number of destinations on a single port. This notice is
## generated when more than :bro:id:`Scan::addr_scan_threshold`
## unique hosts are seen over the previous
## :bro:id:`Scan::addr_scan_interval` time range.
Address_Scan,
## Port scans detect that an attacking host appears to be
## scanning a single victim host on several ports. This notice
## is generated when an attacking host attempts to connect to
## :bro:id:`Scan::port_scan_threshold`
## unique ports on a single host over the previous
## :bro:id:`Scan::port_scan_interval` time range.
Port_Scan,
};
## Failed connection attempts are tracked over this time interval for
## the address scan detection. A higher interval will detect slower
## scanners, but may also yield more false positives.
const addr_scan_interval = 5min &redef;
## Failed connection attempts are tracked over this time interval for
## the port scan detection. A higher interval will detect slower
## scanners, but may also yield more false positives.
const port_scan_interval = 5min &redef;
## The threshold of the unique number of hosts a scanning host has to
## have failed connections with on a single port.
const addr_scan_threshold = 25.0 &redef;
## The threshold of the number of unique ports a scanning host has to
## have failed connections with on a single victim host.
const port_scan_threshold = 15.0 &redef;
global Scan::addr_scan_policy: hook(scanner: addr, victim: addr, scanned_port: port);
global Scan::port_scan_policy: hook(scanner: addr, victim: addr, scanned_port: port);
}
event bro_init() &priority=5
{
local r1: SumStats::Reducer = [$stream="scan.addr.fail", $apply=set(SumStats::UNIQUE), $unique_max=double_to_count(addr_scan_threshold+2)];
SumStats::create([$name="addr-scan",
$epoch=addr_scan_interval,
$reducers=set(r1),
$threshold_val(key: SumStats::Key, result: SumStats::Result) =
{
return result["scan.addr.fail"]$unique+0.0;
},
#$threshold_func=check_addr_scan_threshold,
$threshold=addr_scan_threshold,
$threshold_crossed(key: SumStats::Key, result: SumStats::Result) =
{
local r = result["scan.addr.fail"];
local side = Site::is_local_addr(key$host) ? "local" : "remote";
local dur = duration_to_mins_secs(r$end-r$begin);
local message=fmt("%s scanned at least %d unique hosts on port %s in %s", key$host, r$unique, key$str, dur);
NOTICE([$note=Address_Scan,
$src=key$host,
$p=to_port(key$str),
$sub=side,
$msg=message,
$identifier=cat(key$host)]);
}]);
# Note: port scans are tracked similar to: table[src_ip, dst_ip] of set(port);
local r2: SumStats::Reducer = [$stream="scan.port.fail", $apply=set(SumStats::UNIQUE), $unique_max=double_to_count(port_scan_threshold+2)];
SumStats::create([$name="port-scan",
$epoch=port_scan_interval,
$reducers=set(r2),
$threshold_val(key: SumStats::Key, result: SumStats::Result) =
{
return result["scan.port.fail"]$unique+0.0;
},
$threshold=port_scan_threshold,
$threshold_crossed(key: SumStats::Key, result: SumStats::Result) =
{
local r = result["scan.port.fail"];
local side = Site::is_local_addr(key$host) ? "local" : "remote";
local dur = duration_to_mins_secs(r$end-r$begin);
local message = fmt("%s scanned at least %d unique ports of host %s in %s", key$host, r$unique, key$str, dur);
NOTICE([$note=Port_Scan,
$src=key$host,
$dst=to_addr(key$str),
$sub=side,
$msg=message,
$identifier=cat(key$host)]);
}]);
}
function add_sumstats(id: conn_id, reverse: bool)
{
local scanner = id$orig_h;
local victim = id$resp_h;
local scanned_port = id$resp_p;
if ( reverse )
{
scanner = id$resp_h;
victim = id$orig_h;
scanned_port = id$orig_p;
}
if ( hook Scan::addr_scan_policy(scanner, victim, scanned_port) )
SumStats::observe("scan.addr.fail", [$host=scanner, $str=cat(scanned_port)], [$str=cat(victim)]);
if ( hook Scan::port_scan_policy(scanner, victim, scanned_port) )
SumStats::observe("scan.port.fail", [$host=scanner, $str=cat(victim)], [$str=cat(scanned_port)]);
}
function is_failed_conn(c: connection): bool
{
# Sr || ( (hR || ShR) && (data not sent in any direction) )
if ( (c$orig$state == TCP_SYN_SENT && c$resp$state == TCP_RESET) ||
(((c$orig$state == TCP_RESET && c$resp$state == TCP_SYN_ACK_SENT) ||
(c$orig$state == TCP_RESET && c$resp$state == TCP_ESTABLISHED && "S" in c$history )
) && /[Dd]/ !in c$history )
)
return T;
return F;
}
function is_reverse_failed_conn(c: connection): bool
{
# reverse scan i.e. conn dest is the scanner
# sR || ( (Hr || sHr) && (data not sent in any direction) )
if ( (c$resp$state == TCP_SYN_SENT && c$orig$state == TCP_RESET) ||
(((c$resp$state == TCP_RESET && c$orig$state == TCP_SYN_ACK_SENT) ||
(c$resp$state == TCP_RESET && c$orig$state == TCP_ESTABLISHED && "s" in c$history )
) && /[Dd]/ !in c$history )
)
return T;
return F;
}
event connection_attempt(c: connection)
{
local is_reverse_scan = F;
if ( "H" in c$history )
is_reverse_scan = T;
add_sumstats(c$id, is_reverse_scan);
}
event connection_rejected(c: connection)
{
local is_reverse_scan = F;
if ( "s" in c$history )
is_reverse_scan = T;
add_sumstats(c$id, is_reverse_scan);
}
event connection_reset(c: connection)
{
if ( is_failed_conn(c) )
add_sumstats(c$id, F);
else if ( is_reverse_failed_conn(c) )
add_sumstats(c$id, T);
}
event connection_pending(c: connection)
{
if ( is_failed_conn(c) )
add_sumstats(c$id, F);
else if ( is_reverse_failed_conn(c) )
add_sumstats(c$id, T);
}
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