Creation or Modification of Pluggable Authentication Module or Configuration

 1[metadata]
 2creation_date = "2024/03/06"
 3integration = ["endpoint"]
 4maturity = "production"
 5updated_date = "2024/07/18"
 6
 7[rule]
 8author = ["Elastic"]
 9description = """
10This rule monitors for the creation or modification of Pluggable Authentication Module (PAM) shared object files or
11configuration files. Attackers may create or modify these files to maintain persistence on a compromised system, or 
12harvest account credentials.
13"""
14false_positives = [
15    "Trusted system module updates or allowed Pluggable Authentication Module (PAM) daemon configuration changes.",
16]
17from = "now-9m"
18index = ["logs-endpoint.events.file*"]
19language = "eql"
20license = "Elastic License v2"
21name = "Creation or Modification of Pluggable Authentication Module or Configuration"
22references = [
23    "https://github.com/zephrax/linux-pam-backdoor",
24    "https://github.com/eurialo/pambd",
25    "http://0x90909090.blogspot.com/2016/06/creating-backdoor-in-pam-in-5-line-of.html",
26    "https://www.trendmicro.com/en_us/research/19/i/skidmap-linux-malware-uses-rootkit-capabilities-to-hide-cryptocurrency-mining-payload.html",
27]
28risk_score = 47
29rule_id = "f48ecc44-7d02-437d-9562-b838d2c41987"
30severity = "medium"
31tags = [
32    "Domain: Endpoint",
33    "OS: Linux",
34    "Use Case: Threat Detection",
35    "Tactic: Credential Access",
36    "Tactic: Persistence",
37    "Data Source: Elastic Defend",
38]
39timestamp_override = "event.ingested"
40type = "eql"
41query = '''
42file where host.os.type == "linux" and event.action in ("rename", "creation") and 
43process.executable != null and (
44  (file.path : ("/lib/security/*", "/lib64/security/*", "/usr/lib/security/*", "/usr/lib64/security/*",
45  "/usr/lib/x86_64-linux-gnu/security/*") and file.extension == "so") or
46  (file.path : "/etc/pam.d/*" and file.extension == null) or 
47  (file.path : "/etc/security/pam_*" or file.path == "/etc/pam.conf")
48) and not (
49  process.executable in (
50    "/bin/dpkg", "/usr/bin/dpkg", "/bin/dockerd", "/usr/bin/dockerd", "/usr/sbin/dockerd", "/bin/microdnf",
51    "/usr/bin/microdnf", "/bin/rpm", "/usr/bin/rpm", "/bin/snapd", "/usr/bin/snapd", "/bin/yum", "/usr/bin/yum",
52    "/bin/dnf", "/usr/bin/dnf", "/bin/podman", "/usr/bin/podman", "/bin/dnf-automatic", "/usr/bin/dnf-automatic",
53    "/bin/pacman", "/usr/bin/pacman", "/usr/bin/dpkg-divert", "/bin/dpkg-divert", "/sbin/apk", "/usr/sbin/apk",
54    "/usr/local/sbin/apk", "/usr/bin/apt", "/usr/sbin/pacman", "/bin/podman", "/usr/bin/podman", "/usr/bin/puppet",
55    "/bin/puppet", "/opt/puppetlabs/puppet/bin/puppet", "/usr/bin/chef-client", "/bin/chef-client",
56    "/bin/autossl_check", "/usr/bin/autossl_check", "/proc/self/exe", "/dev/fd/*",  "/usr/bin/pamac-daemon",
57    "/bin/pamac-daemon", "/usr/lib/snapd/snapd", "/usr/local/bin/dockerd", "/usr/sbin/pam-auth-update",
58    "/usr/lib/systemd/systemd", "/usr/libexec/packagekitd", "/usr/bin/bsdtar", "/sbin/pam-auth-update"
59  ) or
60  file.path : (
61    "/tmp/snap.rootfs_*/pam_*.so", "/tmp/newroot/lib/*/pam_*.so", "/tmp/newroot/usr/lib64/security/pam_*.so"
62  ) or
63  file.extension in ("swp", "swpx", "swx", "dpkg-remove") or
64  file.Ext.original.extension == "dpkg-new" or
65  process.executable : (
66    "/nix/store/*", "/var/lib/dpkg/*", "/snap/*", "/dev/fd/*", "/usr/lib/virtualbox/*"
67  ) or
68  (process.name == "sed" and file.name : "sed*") or
69  (process.name == "perl" and file.name : "e2scrub_all.tmp*") 
70)
71'''
72
73[[rule.threat]]
74framework = "MITRE ATT&CK"
75
76[[rule.threat.technique]]
77id = "T1543"
78name = "Create or Modify System Process"
79reference = "https://attack.mitre.org/techniques/T1543/"
80
81[rule.threat.tactic]
82id = "TA0003"
83name = "Persistence"
84reference = "https://attack.mitre.org/tactics/TA0003/"
85
86[[rule.threat]]
87framework = "MITRE ATT&CK"
88
89[[rule.threat.technique]]
90id = "T1556"
91name = "Modify Authentication Process"
92reference = "https://attack.mitre.org/techniques/T1556/"
93
94[rule.threat.tactic]
95id = "TA0006"
96name = "Credential Access"
97reference = "https://attack.mitre.org/tactics/TA0006/"