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TLS Bleichenbacher Attack Vulnerability

An error in the way Transport Layer Security (TLS) implements RSA encryption may leave it vulnerable to a Bleichenbacher-style attack.
Threat ID:
CC-1856
Category:
Threat Severity:
Medium
Threat Vector:
Published:
14 December 2017 12:00 AM
Report a cyber attack: call 0300 303 5222 or email [email protected]

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This article no longer conforms to NHS Digital's standards for cyber alerts, and may contain outdated or inaccurate information. Use of this information contained in this page is at your own risk

Summary

An error in the way Transport Layer Security (TLS) implements RSA encryption may leave it vulnerable to a Bleichenbacher-style attack.

Threat details

Poor implementations of the RFC 5246 standard may leak information when handling PKCS#1 padding errors. These errors may allow an attack to discern between valid and invalid messages, and could be used to gain access to the pre-master private RSA key (i.e. TLS session key). This key could then be used by a remote, unauthenticated attacker to decrypt TLS traffic.

Remediation steps

Type Step
  • If possible, disable use of RSA with TLS.
  • Check for released vendor patches.
  • Specific advice on defending against Bleichenbacher-style attacks can be found here.

Last edited: 17 February 2020 11:40 am