Cisco Type 4 Hash

What is Cisco Type 4?

Cisco Type 4 (also known as **MD5-Cisco** or **MD5 with Cisco-style hashing**) is a proprietary cryptographic hash format derived from the MD5 algorithm, originally introduced by Cisco Systems in the late 1990s to secure password storage in its IOS and Catalyst OS platforms. Structurally, it extends MD5 by prepending a 16-byte salt (derived from the username and a fixed Cisco-specific seed) and appending a 16-byte "magic" value (0x0000000000000000) before hashing the concatenated string. The resulting 128-bit hash is stored in a 32-character hexadecimal string, typically truncated to 16 characters in Cisco implementations. This format was primarily used to authenticate user access via the **enable** and **username** commands, though it was later deprecated in favor of stronger mechanisms like SHA-256 or AES encryption due to its cryptographic weaknesses.

The vulnerability of Cisco Type 4 stems from its reliance on a predictable salt derivation (lacking true randomness) and the inherent fragility of MD5 against brute-force attacks. Without a unique per-password salt, attackers can leverage **rainbow tables** or **precomputed hash databases** to reverse-engineer credentials efficiently. Additionally, the format’s reliance on CPU-bound MD5 operations makes it susceptible to **GPU/FPGA acceleration** via tools like Hashcat, which can crack millions of hashes per second. Collision resistance is further compromised by MD5’s known vulnerabilities, including the **Boomerang attack** and **length-extension exploits**, while the fixed structure enables **dictionary-based attacks** when combined with weak passwords. These flaws render Cisco Type 4 unsuitable for modern security standards, despite its historical role in legacy Cisco systems.

Identifying Cisco Type 4 Hashes

Identifying a hash blindly is often difficult because multiple algorithms can output strings of the exact same length. For example, a standard 32-character hexadecimal string could be MD5, NTLM, MD4, or LM. To definitively identify Cisco Type 4, security researchers analyze the hash against a strict regular expression (regex) signature (shown above) to find structural matches.

How to Crack Cisco Type 4

If you need to recover the plaintext password for a Cisco Type 4 hash during a penetration test or forensics investigation, you must supply the correct module ID to your cracking software. Use the exact commands provided at the top of this page to target the hash successfully.