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Date: Tue, 11 May 2021 20:55:17 +0000
From: Qualys Security Advisory <qsa@...lys.com>
To: null p0int3r <nullp0int3rx@...il.com>
CC: "oss-security@...ts.openwall.com" <oss-security@...ts.openwall.com>
Subject: Re: [CVE-2020-28018] Use-After-Free on Exim Question
Hi,
On Tue, May 11, 2021 at 01:23:43PM +0200, null p0int3r wrote:
> So I suppose that command is the first you send after the second
> "STARTTLS" command being sent right?
Yes! After the second STARTTLS we send an invalid MAIL FROM command (for
example, "MAIL FROM:(\"${run{...}}\")\n"). Exim then responds with a 501
error message that includes our "${run{...}}" string, and since corked
in tls_write() is still non-NULL, this string is written to where the
used-after-free corked points to.
Hopefully this helps!
> PD: Congrats for those nice bugs discovered.
Thank you very much for your mail!
With best regards,
--
the Qualys Security Advisory team
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