mirror of
https://github.com/valitydev/SigmaHQ.git
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226 lines
7.9 KiB
Python
Executable File
226 lines
7.9 KiB
Python
Executable File
#!/usr/bin/env python3
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# Convert Sigma rules with EventIDs to rules with generic log sources
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from argparse import ArgumentParser
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import yaml
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import sys
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from pathlib import Path
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from sigma.output import SigmaYAMLDumper
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class Output(object):
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"""Output base class"""
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def write(self, *args, **kwargs):
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self.f.write(*args, **kwargs)
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class SingleFileOutput(Output):
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"""Output into single file with multiple YAML documents. Each input file is announced with comment."""
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def __init__(self, name):
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self.f = open(name, "x")
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self.path = None
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self.first = True
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def new_output(self, path):
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"""Announce new Sigma rule as input and start new YAML document."""
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if self.path is None or self.path != path:
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if self.first:
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self.first = False
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else:
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self.f.write("---\n")
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self.path = path
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self.f.write("# Sigma rule: {}\n".format(path))
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def finish(self):
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self.f.close()
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class StdoutOutput(SingleFileOutput):
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"""Like SingleFileOutput, just for standard output"""
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def __init__(self):
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self.f = sys.stdout
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self.path = None
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self.first = True
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def finish(self):
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pass
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class DirectoryOutput(Output):
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"""Output each input file into a corresponding output file in target directory."""
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def __init__(self, dirpath):
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self.d = dirpath
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self.f = None
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self.path = None
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self.opened = None
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def new_output(self, path):
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if self.path is None or self.path != path:
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if self.f is not None:
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self.f.close()
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self.path = path
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self.opened = False # opening file is deferred to first write
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def write(self, *args, **kwargs):
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if not self.opened:
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self.f = (self.d / self.path.name).open("x")
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super().write(*args, **kwargs)
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def finish(self):
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if self.f is not None:
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self.f.close()
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def get_output(output):
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if output is None:
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return StdoutOutput()
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path = Path(output)
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if path.is_dir():
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return DirectoryOutput(path)
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else:
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return SingleFileOutput(output)
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class AmbiguousRuleException(TypeError):
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def __init__(self, ids):
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super().__init__()
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self.ids = ids
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def __str__(self):
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return(", ".join([str(eid) for eid in self.ids]))
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def convert_to_generic(yamldoc):
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changed = False
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try:
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product = yamldoc["logsource"]["product"]
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service = yamldoc["logsource"]["service"]
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except KeyError:
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return False
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if product == "windows" and service in ("sysmon", "security"):
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# Currently, only Windows Security or Sysmon are relevant
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eventids = set()
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for name, detection in yamldoc["detection"].items(): # first collect all event ids
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if name == "condition" or type(detection) is not dict:
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continue
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try:
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eventid = detection["EventID"]
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try: # expect that EventID attribute contains a list
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eventids.update(eventid)
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except TypeError: # if this fails, it's a plain value
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eventids.add(eventid)
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except KeyError: # No EventID attribute
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pass
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if 1 in eventids and service == "sysmon" or \
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4688 in eventids and service == "security":
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if len(eventids) == 1: # only convert if one EventID collected, else it gets complicated
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# remove all EventID definitions
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empty_name = list()
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for name, detection in yamldoc["detection"].items():
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if name == "condition" or type(detection) is not dict:
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continue
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try:
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del detection["EventID"]
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except KeyError:
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pass
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if detection == {}: # detection was reduced to nothing - remove it later
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empty_name.append(name)
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for name in empty_name: # delete empty detections
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del yamldoc["detection"][name]
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if yamldoc["detection"] == {}: # delete detection section if empty
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del yamldoc["detection"]
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# rewrite log source
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yamldoc["logsource"] = {
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"category": "process_creation",
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"product": "windows"
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}
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changed = True
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else: # raise an exception to print a warning message to make user aware about the issue
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raise AmbiguousRuleException(eventids)
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return changed
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def get_input_paths(args):
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if args.recursive:
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return [ p for pathname in args.sigma for p in Path(pathname).glob("**/*") if p.is_file() ]
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else:
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return [ Path(sigma) for sigma in args.sigma ]
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argparser = ArgumentParser(description="Convert between classical and generic log source Sigma rules.")
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argparser.add_argument("--output", "-o", help="Output file or directory. Default: standard output.")
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argparser.add_argument("--recursive", "-r", action="store_true", help="Recursive traversal of directory")
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argparser.add_argument("--converted-list", "-c", help="Write list of rule files that were successfully converted (default: stdout)")
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argparser.add_argument("sigma", nargs="+", help="Sigma rule file(s) that should be converted")
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args = argparser.parse_args()
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# Define order-preserving representer from dicts/maps
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def yaml_preserve_order(self, dict_data):
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return self.represent_mapping("tag:yaml.org,2002:map", dict_data.items())
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yaml.add_representer(dict, yaml_preserve_order)
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input_paths = get_input_paths(args)
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output = get_output(args.output)
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if args.converted_list:
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fconv = open(args.converted_list, "w")
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else:
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fconv = sys.stdout
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for path in input_paths:
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try:
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f = path.open("r")
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except OSError as e:
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print("Error while reading Sigma rule {}: {}".format(path, str(e)), file=sys.stderr)
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sys.exit(1)
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try:
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yamldocs = list(yaml.safe_load_all(f))
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except yaml.YAMLError as e:
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print("YAML parse error while parsing Sigma rule {}: {}".format(path, str(e)), file=sys.stderr)
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sys.exit(2)
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yamldoc_num = 0
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changed = False
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for yamldoc in yamldocs:
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yamldoc_num += 1
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output.new_output(path)
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try:
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changed |= convert_to_generic(yamldoc)
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except AmbiguousRuleException as e:
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changed = False
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print("Rule {} in file {} contains multiple EventIDs: {}".format(yamldoc_num, str(path), str(e)), file=sys.stderr)
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yamldocs_idx = list(zip(range(len(yamldocs)), yamldocs))
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delete = set()
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for i, yamldoc_a in yamldocs_idx: # iterate over all yaml document pairs
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for j, yamldoc_b in yamldocs_idx:
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if j <= i: # symmetric relation, skip same comparisons
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continue
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if yamldoc_a == yamldoc_b:
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delete.add(j)
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for i in reversed(sorted(delete)): # delete double yaml documents
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del yamldocs[i]
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# Common special case: two yaml docs, one global and one remainder of multiple following docs - merge them
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try:
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if len(yamldocs) == 2 and \
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yamldocs[0]["action"] == "global" and \
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"action" not in yamldocs[1] and \
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set(yamldocs[0].keys()) & set(yamldocs[1].keys()) == set(): # last condition: no common keys
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yamldocs[0].update(yamldocs[1])
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del yamldocs[1]
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except KeyError:
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pass
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if changed: # only write output if changed
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try:
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output.write(yaml.dump_all(yamldocs, Dumper=SigmaYAMLDumper, indent=4, width=160, default_flow_style=False))
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print(path, file=fconv)
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except OSError as e:
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print("Error while writing result: {}".format(str(e)), file=sys.stderr)
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sys.exit(2)
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output.finish()
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