CERT/CC Vulnerability Note VU#243585

Overview

Some implementations of SSL/TLS accept export-grade (512-bit or smaller) RSA keys even when not specifically requesting export grade ciphers. An attacker able to act as a Man-in-The-Middle (MiTM) could factor weak temporary RSA keys, obtain session keys, and decrypt SSL/TLS trafflc. This issue has been dubbed the "FREAK" (Factoring Attack on RSA-EXPORT Keys) attack.

Description

CWE-757: Selection of Less-Secure Algorithm During Negotiation ('Algorithm Downgrade')

CWE-326: Inadequate Encryption Strength

Some implementations of SSL/TLS accept export-grade (512-bit or smaller) RSA keys even when not specifically requesting export grade ciphers. This can occur when a MiTM attacker asks for export grade ciphers on behalf of a client, and the client insecurely accepts the export grade key. The attacker can then factor the weak RSA key and use this key to decrypt other data necessary to generate the session key. The attacker can then decrypt data in the session.

The researchers provide a more detailed explanation on their website.

Impact

The weak 512-bit "export grade" RSA keys can be factored to allow an attacker to decrypt information encrypted with these keys.

Solution

Update SSL/TLS libraries and applications

Vendors are currently working on patches to address this issue. Affected users are advised to check with the software vendor and update as soon as possible. The Vendor Status information below provides more information for each vendor.

Do not offer export grade ciphers

Configure server and client applications not to use export grade ciphers (EC).