full-disclosure - OpenBSD Security Advisory: Select Boundary Condition

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Message-ID: <20020811210903.GM22399@citi.citi.umich.edu>
From: provos at citi.umich.edu (Niels Provos)
Subject: OpenBSD Security Advisory: Select Boundary Condition

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OpenBSD Security Advisory (adv.select)
Original Release Date: 2002-08-11

1. Systems affected:

        All versions of OpenBSD.

2. Overview:

	Insufficient boundary checks in the select call allow an
	attacker to overwrite kernel memory and execute arbitrary code
	in kernel context.

	Traditionally, the size parameter for the select system call
	is a signed integer.  As a result, the kernel evaluates the
	upper boundary checks in a signed context, so that an attacker
	can circumvent when using certain negative values.

	When the kernel copies the data for the select system call
	from userland the size is used as an unsigned integer which
	causes kernel memory to be overwritten with arbitrary data.

2. Impact:

        Local users can obtain complete system privileges and
        circumvent the extra security measures provided by the
        securelevel system.

3. Solution:

        Apply one of the supplied kernel patches or update to
        3.0-stable or 3.1-stable from 2002-08-11 17:00 EDT or later.

4. Patch:

	ftp://ftp.openbsd.org/pub/OpenBSD/patches/3.1/common/014_scarg.patch

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