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Date: Wed, 12 May 2021 23:46:13 +0000
From: Qualys Security Advisory <>
To: harris.johnson.x <>
CC: "" <>
Subject: Re: [CVE-2020-28018] Use-After-Free on Exim Question


On Wed, May 12, 2021 at 02:46:31PM +0000, harris.johnson.x wrote:
> R u guys using any specific technique to groom the heap / get the
> chunk returned by store_get() on that struct?

We first send a large EHLO command to make sure that the next allocation
will overwrite the freed struct gstring, and then we send the MAIL FROM
command (with an AUTH parameter) to actually overwrite the freed struct
gstring (with arbitrary characters).

Hopefully this helps! With best regards,

the Qualys Security Advisory team


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