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iocitrix.py
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iocitrix.py
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#!/usr/bin/env python3
#
# file: iocitrix.py
#
# $ python3 iocitrix.py netscaler-image.vmx
#
# author: Fox-IT Security Research Team <[email protected]>
#
import argparse
import re
from typing import Iterator
try:
from tabulate import tabulate
except ImportError:
raise ImportError("tabulate missing, please use `pip install tabulate`")
try:
from dissect.target import Target
from dissect.target.tools.info import print_target_info
from dissect.util.ts import from_unix
from flow.record import RecordDescriptor
except ImportError:
raise ImportError("dissect missing, please use `pip install dissect`")
EXPECTED_PHP_FILE_PERMISSION = 0o444
SUSPICIOUS_PHP_CONTENTS = {"eval($_", "base64_decode(", "http_status_code(", "http_status_code(", "array_filter("}
MAXIMUM_BYTE_SIZE_PHP_TO_CHECK_CONTENTS = 2048
# Difference of two weeks between modification time and changed time
TIMESTOMP_THRESHOLD_SECONDS = (60 * 60) * 24 * 7 * 2
WEBSHELL_PATHS = [
"/var/netscaler/logon/",
"/var/vpn/",
"/var/netscaler/ns_gui/",
]
TIMESTOMP_DIRS = WEBSHELL_PATHS + ["/var/tmp"]
KNOWN_SUID_BINARIES = [
"/netscaler/ping",
"/netscaler/ping6",
"/netscaler/traceroute",
"/netscaler/traceroute6",
"/sbin/mksnap_ffs",
"/sbin/shutdown",
"/sbin/poweroff",
"/usr/bin/crontab",
"/usr/bin/lock",
"/usr/bin/login",
"/usr/bin/passwd",
"/usr/bin/yppasswd",
"/usr/bin/su",
"/usr/libexec/ssh-keysign",
"/bin/umount",
"/bin/ping",
"/bin/mount",
"/bin/su",
"/bin/ping6",
"/lib64/dbus-1/dbus-daemon-launch-helper",
"/usr/bin/atq",
"/usr/bin/at",
"/usr/bin/sudo",
"/usr/bin/newgrp",
"/usr/bin/chsh",
"/usr/bin/sg",
"/usr/bin/gpasswd",
"/usr/bin/chfn",
"/usr/bin/sudoedit",
"/usr/bin/staprun",
"/usr/bin/atrm",
"/usr/bin/chage",
"/usr/libexec/openssh/ssh-keysign",
"/usr/sbin/userhelper",
"/usr/sbin/usernetctl",
"/usr/sbin/ping6",
"/opt/likewise/bin/ksu",
"/sbin/umount.nfs",
"/sbin/pam_timestamp_check",
"/sbin/unix_chkpwd",
"/sbin/mount.nfs",
"/sbin/mount.nfs4",
"/sbin/umount.nfs4",
]
EVIL_CRONTAB_CONTENTS = [
("ip address ", re.compile(r"([0-9]{1,3}\.){3}[0-9]{1,3}")),
("/var/tmp", re.compile("/var/tmp")),
("nobody user", re.compile("nobody")),
]
FindingRecord = RecordDescriptor(
"ioc/hit",
[
("string", "type"),
("string", "alert"),
("string", "confidence"),
("string", "path"),
],
)
def check_suspicious_php_files(target: Target, start_path) -> Iterator[FindingRecord]:
if not target.fs.exists(start_path):
return
for path in target.fs.path(start_path).rglob("*.php"):
stat = path.stat()
mode = stat.st_mode & 0o777
if mode != EXPECTED_PHP_FILE_PERMISSION:
permission_printable = oct(mode)
yield FindingRecord(
alert=f"Suspicious php permission {permission_printable}",
confidence="high",
path=path,
type="php-file-permission",
)
if stat.st_size > MAXIMUM_BYTE_SIZE_PHP_TO_CHECK_CONTENTS:
continue
with path.open("rt") as php_file:
for line in php_file:
for evil in SUSPICIOUS_PHP_CONTENTS:
if evil.lower() in line.lower():
yield FindingRecord(
type="php-file-contents",
path=path,
confidence="high",
alert=f"Suspicious PHP code '{evil}'",
)
def check_suid_binaries(target: Target) -> Iterator[tuple[str, str]]:
for suid_binary_record in target.suid_binaries():
if suid_binary_record.path in KNOWN_SUID_BINARIES:
continue
yield FindingRecord(
type="binary/suid",
alert="Binary with SUID bit set Observed",
confidence="medium",
path=suid_binary_record.path,
)
def check_crontabs(target: Target):
for cronjob_record in target.cronjobs():
if cronjob_record._desc.name == "linux/environmentvariable":
continue
if cronjob_record.user in ["nobody"]:
yield FindingRecord(
type="cronjob/user",
alert="Crontab by nobody user observed",
confidence="high",
path=cronjob_record.path,
)
for evil_check in EVIL_CRONTAB_CONTENTS:
name, pattern = evil_check
if match := pattern.match(cronjob_record.command):
yield FindingRecord(
type="cronjob/command",
alert=f"{name} find in crontab comand ({match.group(0)})",
confidence="medium",
path=cronjob_record.path,
)
def check_timestomps(target: Target):
for timestomp_dir in TIMESTOMP_DIRS:
for entry in target.fs.path(timestomp_dir).rglob("*"):
if not entry.exists():
continue
stat = entry.lstat()
modification_time = from_unix(stat.st_mtime)
changed_time = from_unix(stat.st_ctime)
difference = changed_time - modification_time
if difference.seconds > TIMESTOMP_THRESHOLD_SECONDS:
yield FindingRecord(
type="file/timestomp",
alert=f"Possibly Timestomped File Observed ({difference.seconds} seconds)",
confidence="medium",
path=entry.path,
)
def ioc_check_target(target: Target) -> list[FindingRecord]:
findings = []
print("\n*** Checking for webshells ***\n")
for path in WEBSHELL_PATHS:
for finding in check_suspicious_php_files(target, path):
print(finding)
findings.append(finding)
print("\n*** Checking for timestomped files ***\n")
for finding in check_timestomps(target):
print(finding)
findings.append(finding)
print("\n*** Checking for suspicious cronjobs ***\n")
for finding in check_crontabs(target):
print(finding)
findings.append(finding)
print("\n*** Checking for SUID Binaries (this takes a while) ***\n")
for finding in check_suid_binaries(target):
print(finding)
findings.append(finding)
return findings
def check_targets(target_paths: list[str]) -> None:
for path in target_paths:
target = Target.open(path)
if target.os != "citrix-netscaler":
raise ValueError(f"Target not recognized as a citrix-netscaler: {target.path}: {target.os}")
print_target_info(target)
print("")
target_findings = ioc_check_target(target)
if len(target_findings) == 0:
print("[*] No hits found for IOC checks.")
else:
print("")
print("********************************************************************************")
print("*** ***")
print("*** There were findings for Indicators of Compromise. ***")
print("*** Please consider performing further forensic investigation of the system. ***")
print("*** ***")
print("********************************************************************************")
print("")
# Display in table format
table_entries = []
for finding in target_findings:
table_entries.append(
{
"Confidence": finding.confidence,
"Type": finding.type,
"Alert": finding.alert,
"Artefact Location": finding.path,
}
)
print(tabulate(table_entries, headers="keys"))
print("\n\n")
print("All targets analyzed.")
def main() -> None:
parser = argparse.ArgumentParser(description="Analyze forensic images of Citrix Netscalers for IOCs")
parser.add_argument("targets", metavar="TARGETS", nargs="+", help="Target(s) to load")
args = parser.parse_args()
check_targets(args.targets)
if __name__ == "__main__":
main()