Re: heartbleed OpenSSL bug CVE-2014-0160

[Daniel Franke <dfoxfranke () gmail com>]

On 4/9/14, Fabien Bourdaire <lists () ecsc 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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