CVE-2025-26690

Executive Summary

CVE-2025-26690 is a denial-of-service (DoS) vulnerability in OpenHarmony, an open-source operating system for IoT and edge devices. The flaw resides in a NULL pointer dereference that can be triggered by a local attacker with low privileges. Successful exploitation causes the system to crash, leading to a temporary denial of service. The vulnerability affects OpenHarmony v5.0.3 and all prior versions. No public exploit code or proof-of-concept is currently available, and no official patch has been released. The CVSS score is 3.3 (Low), reflecting the requirement for local access and the limited impact (availability only). The EPSS score is 0.0%, indicating a very low probability of exploitation in the wild at this time.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
• Base Score: 3.3 (Low)
• Attack Vector: Local (AV:L) – The attacker must have local access to the device.
• Attack Complexity: Low (AC:L) – No special conditions are required.
• Privileges Required: Low (PR:L) – The attacker needs basic user-level privileges.
• User Interaction: None (UI:N) – No user action is needed.
• Scope: Unchanged (S:U) – The impact is confined to the vulnerable component.
• Confidentiality Impact: None (C:N)
• Integrity Impact: None (I:N)
• Availability Impact: Low (A:L) – The system becomes temporarily unavailable due to a crash.

Threat Level: Low. The vulnerability requires local access and low privileges, limiting the attack surface. The impact is limited to availability, and no public exploit exists. However, in IoT/edge environments where uptime is critical, even a low-severity DoS can be disruptive.

Deep Dive & Mechanics

The vulnerability is a classic NULL pointer dereference (CWE-476). In OpenHarmony, a system service or kernel component fails to properly validate a pointer before dereferencing it. A local attacker can craft a specific input or system call that causes the pointer to be NULL, leading to a crash.

Root Cause Analysis:

• The vulnerable code path likely involves a function that receives a pointer from user space or from an internal data structure.
• The pointer is used without a NULL check, assuming it is always valid.
• An attacker can manipulate the input to make the pointer NULL, triggering a segmentation fault or kernel panic.

Attack Scenario:

1. The attacker gains local access to an OpenHarmony device (e.g., via a compromised app or SSH).
2. The attacker executes a crafted system call or writes to a specific file descriptor.
3. The vulnerable function dereferences a NULL pointer.
4. The operating system crashes, causing a denial of service.

Affected Component: The exact component is not disclosed, but based on the nature of the vulnerability, it is likely a kernel module or a system service that handles user input.

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code pattern is described generically.

Vulnerable Code (C-like pseudocode):

void vulnerable_function(void *ptr) {
    // No NULL check
    int value = *(int *)ptr;  // Dereference without validation
    // ... use value
}

Patched Code (Hypothetical):

void patched_function(void *ptr) {
    if (ptr == NULL) {
        // Handle error gracefully
        return -EINVAL;
    }
    int value = *(int *)ptr;
    // ... use value
}

The fix involves adding a NULL pointer check before dereferencing. The function should return an error code or handle the NULL case without crashing.

Exploitation & Lab Setup

Red Team

Prerequisites:

• Local access to an OpenHarmony device (v5.0.3 or earlier).
• Low-privilege user account.

Exploitation Steps:

1. Identify the vulnerable system call or file descriptor. (This requires reverse engineering or fuzzing.)
2. Craft a payload that triggers the NULL pointer dereference. For example, if the vulnerability is in a write() handler, send a buffer with a specific structure that causes a pointer to be NULL.
3. Execute the payload:

   echo -n -e '\x00\x00\x00\x00' > /proc/vulnerable_file
   

   or

   // Example C code
   int fd = open("/dev/vulnerable_device", O_RDWR);
   write(fd, NULL, 0);  // Trigger NULL pointer
   

4. Observe the system crash (kernel panic or service termination).

Note: No public exploit exists. The above is a generic example.

Blue Team

Detection:

• Monitor for unexpected crashes or kernel panics in system logs.
• Look for repeated attempts to access specific device files or system calls with unusual parameters.
• Use the detection rules provided in the Detection Engineering section.

Mitigation:

• Restrict local access to trusted users only.
• Apply the principle of least privilege.
• Monitor for anomalous system behavior.

Indicators of Compromise (IOCs)

• System Logs: Kernel panic messages or segmentation faults in /var/log/messages or dmesg.
• Crash Dumps: Core dumps or crash logs in /var/crash/.
• Process Behavior: A process repeatedly opening and writing to /dev/vulnerable_device or similar.
• Network: No network-based IOCs, as the attack is local.

Example Log Entry:

[ 1234.5678] Unable to handle kernel NULL pointer dereference at virtual address 00000000
[ 1234.5679] Internal error: Oops: 5 [#1] SMP ARM

Detection Engineering

YARA Rule

rule CVE_2025_26690_NULL_PTR_DEREF {
    meta:
        description = "Detects potential NULL pointer dereference in OpenHarmony crash logs"
        author = "Valters IT"
        date = "2025-04-10"
        cve = "CVE-2025-26690"
    strings:
        $kernel_panic = "Unable to handle kernel NULL pointer dereference"
        $segfault = "segfault at"
        $null_ptr = "NULL pointer dereference"
    condition:
        any of them
}

Sigma Rule

title: OpenHarmony NULL Pointer Dereference Crash
id: 8c7a3b2e-1f4d-4a9e-8c6b-5d3e2f1a0b9c
status: experimental
description: Detects kernel panics or crashes indicative of CVE-2025-26690 exploitation
author: Valters IT
date: 2025-04-10
logsource:
    product: linux
    service: kernel
detection:
    selection:
        - EventID: 1  # Kernel panic
        - Message|contains: 'NULL pointer dereference'
        - Message|contains: 'Unable to handle kernel'
    condition: selection
falsepositives:
    - Genuine kernel bugs
level: medium

Suricata Rule

alert tcp any any -> any any (msg:"CVE-2025-26690 OpenHarmony NULL Pointer Dereference Attempt"; content:"|00 00 00 00|"; depth:4; sid:1000001; rev:1;)

Note: This Suricata rule is a placeholder. Since the attack is local, network-based detection is not directly applicable. The rule above would only detect if the exploit payload is sent over the network, which is unlikely.

Remediation & Mitigation

Immediate Actions:

1. Restrict Local Access: Limit user accounts and enforce strong authentication.
2. Monitor Logs: Watch for kernel panics or segmentation faults.
3. Apply Workarounds: If the vulnerable component is identified, disable it or restrict access via permissions.

Long-Term Fix:

• Apply the official patch when released by OpenHarmony.
• Update to a patched version (none available at this time).
• Implement input validation and NULL pointer checks in custom code.

Vendor Contact: OpenHarmony community (https://gitee.com/openharmony).

Valters IT