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Date: Tue, 14 Nov 2023 20:07:13 +0100
From: Solar Designer <>
To: Antonio Gomez Iglesias <>
Cc:, Tavis Ormandy <>
Subject: Re: CVE-2023-23583: Intel - Denial of Service - Privilege Escalation (Reptar)

On Tue, Nov 14, 2023 at 10:31:51AM -0800, Antonio Gomez Iglesias wrote:
> Name of the issue: Redundant Prefix Issue
> Description of the issue
> Under certain microarchitectural conditions, Intel has identified cases
> where execution of an instruction (REP MOVSB) encoded with a redundant
> REX prefix may result in unpredictable system behavior resulting in a
> system crash/hang, or, in some limited scenarios, may allow escalation
> of privilege from CPL3 to CPL0.
> This Redundant Prefix Issue is assigned CVE-2023-23583 with a CVSS Base
> Score of 8.8 High CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H.
> Mitigation
> Intel is providing a microcode update to mitigate this issue:

Thank you, Antonio!

Here's a writeup and reproducer tool by Tavis Ormandy:

The GitHub release page above links to Intel security advisory:

which specifies what CPU generations are affected (from 10th generation
Intel Core or 3rd generation Xeon Scalable to current), and links to a
table with "an exhaustive list of processors" matched against this issue
and previously disclosed issues:

It also says "Please refer to the technical paper here for additional
information", where "here" is a link supposedly to "the technical
paper", but it's a non-existent page currently, so I'm not posting the
URL yet (not sure if it'll stay the same when the page is published).

Meanwhile, Tavis' writeup is great!


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