Weak TLS_DHE_RSA_WITH_AES_256_CBC_SHA256
- IANA name:
- TLS_DHE_RSA_WITH_AES_256_CBC_SHA256
- OpenSSL name:
- DHE-RSA-AES256-SHA256
- GnuTLS name:
- TLS_DHE_RSA_AES_256_CBC_SHA256
- Hex code:
- 0x00, 0x6B
- TLS Version(s):
- TLS1.2, TLS1.3
- Protocol:
- Transport Layer Security (TLS)
- Key Exchange:
- PFS Diffie-Hellman Ephemeral (DHE)
- Authentication:
- Rivest Shamir Adleman algorithm (RSA)
- Encryption:
- Advanced Encryption Standard with 256bit key in Cipher Block Chaining mode (AES 256 CBC)
- Hash:
- HMAC Secure Hash Algorithm 256 (SHA256)
- Included in RFC:
- Machine-readable:
- application/json
The so-called DHEat Attack affects cryptographic protocols using the Diffie Hellman key exchange (incl. TLS). According to its authors, it exploits a protocol particularity that may allow attackers to perform a DoS attack "with a low-bandwidth network connection without authentication, privilege, or user interaction."
The so-called Raccoon Attack affects the specifications of TLS 1.2 and below when using a DH(E) key exchange. According to the researchers, while very hard to exploit, in rare circumstances this timing attack allows attackers to decrypt the connection between users and the server. A fix has been introduced in the TLS 1.3 specification.
There are reports that servers using the RSA authentication algorithm with keys longer than 3072-bit may experience heavy performance issues leading to connection timeouts and even service unavailability if many clients open simultaneous connections.
In 2013, researchers demonstrated a timing attack against several TLS implementations using the CBC encryption algorithm (see isg.rhul.ac.uk). Additionally, the CBC mode is vulnerable to plain-text attacks in TLS 1.0, SSL 3.0 and lower. A fix has been introduced with TLS 1.2 in form of the GCM mode which is not vulnerable to the BEAST attack. GCM should be preferred over CBC.