Exam CAS-004 topic 1 question 545 discussion

Given that the server uses obsolete CBC ciphers without strong encryption and lacks forward secrecy, it is susceptible to padding oracle attacks. Allows attackers to decrypt sensitive data or manipulate encrypted messages without knowing the encryption key. - TLS 1.0 is considered insecure due to vulnerabilities. - Obsolete CBC Ciphers (AES, ARIA, etc.) Offered: Cipher Block Chaining (CBC) modes are susceptible to padding oracle attack

This has nothing to do with Padding oracle attack. Example of a padding oracle attack would be: 2025-06-03 22:15:30 [WARN] Decryption Error: Invalid padding detected 2025-06-03 22:15:32 [WARN] TLS_ERROR: Block cipher padding validation failed 2025-06-03 22:15:34 [INFO] Client IP 192.168.1.55 attempted decryption 2025-06-03 22:15:36 [WARN] SIGUSR1 [soft, padding_error] received, restarting session 2025-06-03 22:15:38 [WARN] Decryption Error: Invalid padding detected 2025-06-03 22:15:40 [INFO] Client IP 192.168.1.55 changed encrypted payload 2025-06-03 22:15:42 [WARN] Decryption Error: Invalid padding detected

Given the output from the web application security assessment, the most likely attack to succeed is: A. NULL and unauthenticated cipher downgrade attack.

D While a padding oracle attack is a potential threat, the provided output doesn't directly indicate its susceptibility. The server's support for older, less secure cipher suites, such as RC4 and 3DES, is a more immediate concern. The most likely successful attack in this scenario is a forced downgrade attack. The attacker could exploit the server's support for weaker cipher suites to force the client to negotiate a less secure connection. This could lead to data confidentiality and integrity issues. Therefore, D. On-path forced renegotiation to insecure ciphers remains the most likely attack.

Padding oracle attack: This attack takes advantage of improper validation of padding in cryptographic operations, particularly in block ciphers. If the application provides feedback based on padding errors, this attack could succeed. Based on common vulnerabilities in web applications, if the output suggests any specific issues with padding or cipher handling, C. Padding oracle attack could be the most likely to succeed, especially if the application reveals errors or feedback on cryptographic operations..

Changing answer to C

Since TLS 1.0 is still being offered and more secure protocols are not available, it is likely that a downgrade attack could be used to force the communication to fall back to a weaker, deprecated protocol. Downgrade attacks, including those that lead to NULL ciphers, allow attackers to force weak encryption or no encryption, which aligns with the weaknesses highlighted in this scan. Although NULL ciphers aren't explicitly offered, the downgrade to weak protocols like TLS 1.0 opens the door to various downgrade attacks.