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How to Prevent SSL CRIME

The CRIME (Compression Ratio Info-leak Made Easy) attack is a vulnerability in the SSL compression. The attack against secret web cookies sent over compressed HTTPS or SPDY connections, leaves cookie data vulnerable to session hijacking.

Security Assessment

Security_Assessment_PreventSSLCRIME

CVSS Vector: AV:N/AC:H/AU:N/C:P/I:N/A:N

CRIME Vulnerability Information

As noted, the CRIME attack can be executed against SSL/TLS protocols and the SPDY protocol to hijack a user’s session cookies while they’re still authenticated to a website. 

This can be possible only if the protocols have enabled certain types of data compression methods. While compression can be quite handy in general, it poses the risk of unintentionally revealing clues about the content of the encryption. In particular, the TLS DEFLATE compression scheme was found to be problematic. Its compression algorithm eliminates duplicate strings. 

The CRIME technique was categorized as CVE-2012-4929 by MITRE.

How to prevent the SSL CRIME attack?

To prevent the CRIME vulnerability, disable SSL compression.

Apache

Using the standard settings, CRIME is only a problem for Apache version 2.4.3. To disable SSL compression, define the following directive in your SSL settings (usually /etc/apache2/mods-enabled/ssl.confor /etc/letsencrypt/options-ssl-apache.conf when using Let's Encrypt). Also strongly think of upgrading Apache to the latest version.

SSLCompression off

Nginx

Nginx is vulnerable for CRIME in older versions, which have SSL compression enabled. Please update to a recent version of nginx and OpenSSL. The following versions are known to prevent the vulnerability:

  • 1.0.9 (if OpenSSL 1.0.0+ used)
  • 1.1.6 (if OpenSSL 1.0.0+ used)
  • 1.2.2
  • 1.3.2
apt-get update; apt-get upgrade # Debian / Ubuntu
yum update # RHeL / CentOS
pacman -Syu # Arch Linux

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