full-disclosure - Re: [FD] heartbleed OpenSSL bug CVE-2014-0160

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Date: Wed, 9 Apr 2014 17:04:49 -0400
From: Daniel Franke <dfoxfranke@...il.com>
To: Fabien Bourdaire <lists@...c.co.uk>
Cc: fulldisclosure@...lists.org
Subject: Re: [FD] heartbleed OpenSSL bug CVE-2014-0160

On 4/9/14, Fabien Bourdaire <lists@...c.co.uk> wrote:
> We've created some iptables rules to block all heartbeat queries using
> the very powerful u32 module.
>
> # Block rules
> iptables -t filter -A INPUT  -p tcp --dport 443  -m u32 --u32 \
> "52=0x18030000:0x1803FFFF" -j DROP

It appears to me that this rule assumes that TLS records align with
TCP packet boundaries. Attackers can circumvent it by manipulating
said boundaries. This is, in general, an inherent limitation of trying
to use U32 to filter TCP-based application protocols.

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