TLS implementations may disclose side channel information via discrepancies between valid and invalid PKCS#1 padding, and may therefore be vulnerable to Bleichenbacher-style attacks. This attack is known as a "ROBOT attack".
CWE-203: Information Exposure Through Discrepancy
Transport Layer Security (TLS) is a mechanism for a security transport over network connections, and is defined in RFC 5246. TLS may utilize RSA cryptography to secure the connection, and section 7.4.7 describes how client and server may exchange keys. Implementations that don't closely follow the descriptions in RFC 5246 may leak information to an attacker when they handle PKCS #1 v1.5 padding errors in ways that lets the attacker distinguish between valid and invalid messages. An attacker may utilize discrepancies in TLS error messages to obtain the pre-master secret key private RSA key used by TLS to decrypt sensitive data. This type of attack has become known as a Bleichenbacher attack. CERT/CC previously published CERT Advisory CA-1998-07 for this type of attack.
Some modern cryptographic implementations are vulnerable to Bleichenbacher-style attacks on TLS. While RFC 5246 Section 18.104.22.168 provides advice in order to eliminate discrepancies and defend against Bleichenbacher attacks, implementation-specific error and exception handling may nevertheless re-introduce message discrepancies that act as a cryptographic oracle for a Bleichenbacher-style attack.
More information about the research and affected vendors is available from the researcher's website.
A remote, unauthenticated attacker may be able to obtain the TLS pre-master secret (TLS session key) and decrypt TLS traffic.
Disable TLS RSA
The Vendor Information section below lists implementations and vendors that have been identified as vulnerable TLS implementations. Separate CVE IDs for each vendor have been assigned due to the implementation-specific nature of the vulnerability.
F5 Networks, Inc. Affected
Legion of the Bouncy Castle Affected
Micro Focus Affected
Botan Not Affected
Check Point Software Technologies Not Affected
Dell EMC Not Affected
Fortinet, Inc. Not Affected
GnuTLS Not Affected
IAIK Java Group Not Affected
Microsoft Corporation Not Affected
OpenSSL Not Affected
RSA Security LLC Not Affected
VMware Not Affected
s2n Not Affected
ARM mbed TLS Unknown
Apache HTTP Server Project Unknown
CREDANT Technologies, Inc. Unknown
Crypto++ Library Unknown
Go Programming Language Unknown
IBM, INC. Unknown
Oracle Corporation Unknown
PGP Corporation Unknown
Palo Alto Networks Unknown
aep NETWORKS Unknown
Thanks to Hanno Boeck, Juraj Somorovsky of Ruhr-Universität Bochum / Hackmanit GmbH, and Craig Young of Tripwire VERT for reporting this vulnerability.
This document was written by Garret Wassermann.