Analyzing Active Directory Acl Abuse

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#!/usr/bin/env python3
"""Active Directory ACL abuse detection using ldap3 to find dangerous permissions."""

import argparse
import json
import struct

from ldap3 import Server, Connection, ALL, NTLM, SUBTREE


DANGEROUS_MASKS = {
    "GenericAll": 0x10000000,
    "GenericWrite": 0x40000000,
    "WriteDACL": 0x00040000,
    "WriteOwner": 0x00080000,
    "WriteProperty": 0x00000020,
    "Self": 0x00000008,
    "ExtendedRight": 0x00000100,
    "DeleteChild": 0x00000002,
    "Delete": 0x00010000,
}

ADMIN_SIDS = {
    "S-1-5-18",
    "S-1-5-32-544",
    "S-1-5-9",
}

ADMIN_RID_SUFFIXES = {
    "-500",
    "-512",
    "-516",
    "-518",
    "-519",
    "-498",
}

ATTACK_PATHS = {
    "GenericAll": {
        "user": "Full control allows password reset, Kerberoasting via SPN, or shadow credential attack",
        "group": "Full control allows adding arbitrary members to the group",
        "computer": "Full control allows resource-based constrained delegation attack",
        "organizationalUnit": "Full control allows linking malicious GPO or moving objects",
    },
    "WriteDACL": {
        "user": "Can modify DACL to grant self GenericAll, then reset password",
        "group": "Can modify DACL to grant self write membership, then add self",
        "computer": "Can modify DACL to grant self full control on machine account",
        "organizationalUnit": "Can modify DACL to gain control over OU child objects",
    },
    "WriteOwner": {
        "user": "Can take ownership then modify DACL to escalate privileges",
        "group": "Can take ownership of group then modify membership",
        "computer": "Can take ownership then configure delegation abuse",
        "organizationalUnit": "Can take ownership then control OU policies",
    },
    "GenericWrite": {
        "user": "Can write scriptPath for logon script execution or modify SPN for Kerberoasting",
        "group": "Can modify group attributes including membership",
        "computer": "Can write msDS-AllowedToActOnBehalfOfOtherIdentity for RBCD attack",
        "organizationalUnit": "Can modify OU attributes and link GPO",
    },
}


def is_admin_sid(sid: str, domain_sid: str) -> bool:
    if sid in ADMIN_SIDS:
        return True
    for suffix in ADMIN_RID_SUFFIXES:
        if sid == domain_sid + suffix:
            return True
    return False


def parse_sid(raw: bytes) -> str:
    if len(raw) < 8:
        return ""
    revision = raw[0]
    sub_auth_count = raw[1]
    authority = int.from_bytes(raw[2:8], byteorder="big")
    subs = []
    for i in range(sub_auth_count):
        offset = 8 + i * 4
        if offset + 4 > len(raw):
            break
        subs.append(struct.unpack("<I", raw[offset:offset + 4])[0])
    return f"S-{revision}-{authority}-" + "-".join(str(s) for s in subs)


def parse_acl(descriptor_bytes: bytes) -> list:
    aces = []
    if len(descriptor_bytes) < 20:
        return aces
    revision = descriptor_bytes[0]
    control = struct.unpack("<H", descriptor_bytes[2:4])[0]
    dacl_offset = struct.unpack("<I", descriptor_bytes[16:20])[0]
    if dacl_offset == 0 or dacl_offset >= len(descriptor_bytes):
        return aces
    dacl = descriptor_bytes[dacl_offset:]
    if len(dacl) < 8:
        return aces
    acl_size = struct.unpack("<H", dacl[2:4])[0]
    ace_count = struct.unpack("<H", dacl[4:6])[0]
    offset = 8
    for _ in range(ace_count):
        if offset + 4 > len(dacl):
            break
        ace_type = dacl[offset]
        ace_flags = dacl[offset + 1]
        ace_size = struct.unpack("<H", dacl[offset + 2:offset + 4])[0]
        if ace_size < 4 or offset + ace_size > len(dacl):
            break
        if ace_type in (0x00, 0x05):
            if offset + 8 <= len(dacl):
                access_mask = struct.unpack("<I", dacl[offset + 4:offset + 8])[0]
                sid_offset = offset + 8
                if ace_type == 0x05:
                    sid_offset = offset + 8 + 32
                if sid_offset < offset + ace_size:
                    sid_bytes = dacl[sid_offset:offset + ace_size]
                    sid_str = parse_sid(sid_bytes)
                    matched_perms = []
                    for perm_name, mask_val in DANGEROUS_MASKS.items():
                        if access_mask & mask_val:
                            matched_perms.append(perm_name)
                    if matched_perms:
                        aces.append({
                            "ace_type": "ACCESS_ALLOWED" if ace_type in (0x00, 0x05) else "OTHER",
                            "access_mask": f"0x{access_mask:08x}",
                            "trustee_sid": sid_str,
                            "permissions": matched_perms,
                        })
        offset += ace_size
    return aces


def resolve_sid(conn: Connection, base_dn: str, sid: str) -> str:
    try:
        conn.search(base_dn, f"(objectSid={sid})", attributes=["sAMAccountName", "cn"])
        if conn.entries:
            entry = conn.entries[0]
            return str(entry.sAMAccountName) if hasattr(entry, "sAMAccountName") else str(entry.cn)
    except Exception:
        pass
    return sid


def get_domain_sid(conn: Connection, base_dn: str) -> str:
    conn.search(base_dn, "(objectClass=domain)", attributes=["objectSid"])
    if conn.entries:
        raw = conn.entries[0].objectSid.raw_values[0]
        return parse_sid(raw)
    return ""


def analyze_acls(dc_ip: str, domain: str, username: str, password: str,
                 target_ou: str) -> dict:
    server = Server(dc_ip, get_info=ALL, use_ssl=False)
    domain_parts = domain.split(".")
    base_dn = ",".join(f"DC={p}" for p in domain_parts)
    search_base = target_ou if target_ou else base_dn
    ntlm_user = f"{domain}\\{username}"

    conn = Connection(server, user=ntlm_user, password=password,
                      authentication=NTLM, auto_bind=True)
    domain_sid = get_domain_sid(conn, base_dn)

    conn.search(
        search_base,
        "(|(objectClass=user)(objectClass=group)(objectClass=computer)(objectClass=organizationalUnit))",
        search_scope=SUBTREE,
        attributes=["distinguishedName", "sAMAccountName", "objectClass", "nTSecurityDescriptor"],
    )

    findings = []
    objects_scanned = 0
    sid_cache = {}

    for entry in conn.entries:
        objects_scanned += 1
        dn = str(entry.distinguishedName)
        obj_classes = [str(c) for c in entry.objectClass.values] if hasattr(entry, "objectClass") else []
        obj_type = "unknown"
        for oc in obj_classes:
            if oc.lower() in ("user", "group", "computer", "organizationalunit"):
                obj_type = oc.lower()
                break

        if not hasattr(entry, "nTSecurityDescriptor"):
            continue
        raw_sd = entry.nTSecurityDescriptor.raw_values
        if not raw_sd:
            continue
        sd_bytes = raw_sd[0]
        aces = parse_acl(sd_bytes)

        for ace in aces:
            trustee_sid = ace["trustee_sid"]
            if is_admin_sid(trustee_sid, domain_sid):
                continue
            if trustee_sid not in sid_cache:
                sid_cache[trustee_sid] = resolve_sid(conn, base_dn, trustee_sid)
            trustee_name = sid_cache[trustee_sid]

            for perm in ace["permissions"]:
                if perm in ("Delete", "DeleteChild", "Self", "WriteProperty", "ExtendedRight"):
                    severity = "medium"
                else:
                    severity = "critical"
                attack = ATTACK_PATHS.get(perm, {}).get(obj_type,
                         f"{perm} on {obj_type} may allow privilege escalation")
                findings.append({
                    "severity": severity,
                    "target_object": dn,
                    "target_type": obj_type,
                    "trustee": trustee_name,
                    "trustee_sid": trustee_sid,
                    "permission": perm,
                    "access_mask": ace["access_mask"],
                    "ace_type": ace["ace_type"],
                    "attack_path": attack,
                    "remediation": f"Remove {perm} ACE for {trustee_name} on {dn}",
                })

    conn.unbind()
    findings.sort(key=lambda f: 0 if f["severity"] == "critical" else 1)
    return {
        "domain": domain,
        "domain_sid": domain_sid,
        "search_base": search_base,
        "objects_scanned": objects_scanned,
        "dangerous_aces_found": len(findings),
        "findings": findings,
    }


def main():
    parser = argparse.ArgumentParser(description="Active Directory ACL Abuse Analyzer")
    parser.add_argument("--dc-ip", required=True, help="Domain Controller IP address")
    parser.add_argument("--domain", required=True, help="AD domain name (e.g., corp.example.com)")
    parser.add_argument("--username", required=True, help="Domain username for LDAP bind")
    parser.add_argument("--password", required=True, help="Domain user password")
    parser.add_argument("--target-ou", default=None,
                        help="Target OU distinguished name to scope the search")
    parser.add_argument("--output", default=None, help="Output JSON file path")
    args = parser.parse_args()

    result = analyze_acls(args.dc_ip, args.domain, args.username,
                          args.password, args.target_ou)
    report = json.dumps(result, indent=2)
    if args.output:
        with open(args.output, "w") as f:
            f.write(report)
    print(report)


if __name__ == "__main__":
    main()