Redundant Prefix Issue

ID 793262
Updated 11/15/2023
Version 1.0
Public

Key Takeaways

  • Intel is providing a microcode update to mitigate this issue. No performance impact has been observed nor is expected from this updated microcode. Intel does not expect this issue to be encountered by any non-malicious real-world software.

  • End users do not have to take any special actions to apply these mitigations other than ensuring that their BIOS, system OS, and drivers are up to date. Contact your OEM or OS vendor (OSV) for information on which updates incorporate the latest microcode.

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Disclosure date: 
2023-11-14
Published date: 
2023-11-14
Severity rating: 8.8 High		 Industry-wide severity ratings can be found in the National Vulnerability Database

 

Related Content

Aliases

  • Reptar

Overview

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 (EoP) from CPL3 to CPL0. Intel is providing a microcode update (MCU) to mitigate this issue.

Intel does not expect this issue to be encountered by any non-malicious real-world software. Redundant REX prefixes are not expected to be present in code nor generated by compilers. Malicious exploitation of this issue requires execution of arbitrary code. Intel identified the potential for escalation of privilege in limited scenarios as part of our internal security validation in a controlled Intel lab environment.

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.

For more information, refer to INTEL-SA-00950 and the Chips and Salsa blog at publication time. 

Mitigation

Intel is providing a microcode update to mitigate this issue. No performance impact has been observed nor is expected from this updated microcode.

Some affected processors (including Alder Lake, Raptor Lake and Sapphire Rapids) already received updated microcode prior to November 2023. Refer to the Affected Processors with Microcode Update Versions section below for the specific microcode versions required to mitigate this issue.

Microcode updates are typically included with updates from your original equipment manufacturer (OEM), operating system vendor (OSV), and/or hypervisor vendor. End users do not have to take any special actions to apply these mitigations other than ensuring that their BIOS, system OS, and drivers are up to date. Contact your OEM or OSV for information on which updates incorporate the latest microcode. 

Intel will publish this microcode in Intel’s microcode repository, from which system administrators can download and update the microcode themselves. In situations where a microcode update can be applied at runtime, no reboot is required for this mitigation to be fully effective.

Intel recommends updating affected processors to the microcode version listed in the affected processor table below as soon as possible to mitigate this redundant prefix issue. OSVs may also provide updates containing this new microcode as soon as possible. 

It is also possible for system software to apply a workaround to mitigate this issue by disabling fast strings using the IA32_MISC_ENABLE MSR. Intel does not recommend this approach and has observed that this workaround can incur performance impact of 50% or more on some workloads. By contrast, the recommended microcode mitigation is not expected to have any performance impact.

Affected Processors with Microcode Update Versions

The following in-service and select future processors marked with ‘Y’ should load the microcode listed below to mitigate this redundant prefix issue. After disclosure, this information will be included in the consolidated affected processors table, and distributed as a consolidated .csv file on Intel’s Github*. 

Some newer processors that have already mitigated this issue share the same CPUID with older processors (for example, processors code-named Catlow). It is important that software correctly reports the mitigation status for these processors to avoid performance impacts from applying alternative mitigations.

Processor

Stepping

Code Names / Microarchitectures

Product Family

Affected by Redundant Prefix Issue

Microcode version with Mitigation

Fixed Already

No Action Required

06_3FH

2

Haswell Server EP, EP4S

Intel® Xeon® E processor family

N

 N/A1

N/A

06_3FH

4

Haswell Server EX

Intel® Xeon® E processor family

N

N/A

N/A

06_4FH

1

1. Broadwell Server E, EP, EP4S
2. Broadwell Server EX

1. Intel® Xeon® E processor family
2. Intel® Xeon® E processor family

N

N/A

N/A

06_55H

3

Skylake Server

Intel® Xeon® Scalable processor family

N

N/A

N/A

06_55H

4

1. Skylake Server
2. Skylake D, Bakerville
3. Skylake W
4. Skylake X

1. Intel® Xeon® Scalable processor family
2. Intel® Xeon® D processor family
3. Intel® Xeon® W processor family
4. Intel® Core™ X-series Processors

N

N/A

N/A

06_55H

6

Cascade Lake Server

2nd Generation Intel® Xeon® Scalable processor family

N

N/A

N/A

06_55H

7

1. Cascade Lake Server
2. Cascade Lake W
3. Cascade Lake X

1. 2nd Generation Intel® Xeon® Scalable processor family
2. Intel® Xeon® W processor family
3. Intel® Core™ X-series Processor

N

N/A

N/A

06_55H

A,B

Cooper Lake

3rd Generation Intel® Xeon® Scalable processor family

N

N/A

N/A

06_56H

3

Broadwell DE V2,V3

Intel® Xeon® D processor family

N

N/A

N/A

06_56H

4

Broadwell DE Y0

Intel® Xeon® D processor family

N

N/A

N/A

06_56H

5

1. Broadwell DE A1
2. Hewitt Lake (Broadwell DE)

Intel® Xeon® D processor family

N

N/A

N/A

06_5CH

A

Apollo Lake2

Intel® Atom® Processor E3900 Series

N

N/A

N/A

06_5FH

All

Denverton (Goldmont)

Intel® Atom® C processor family

N

N/A

N/A

06_6AH

All

Ice Lake Xeon-SP

3rd Gen Intel® Xeon® Scalable processor family

Y

0x0d0003b9

N

06_6CH

All

Ice Lake Xeon D

Intel® Xeon® D Processor

Y

0x01000268

N

06_7AH

1

Gemini Lake

1. Intel® Pentium® Processor Silver Series
2. Intel® Celeron® Processor J Series
3. Intel® Celeron® Processor N Series

N

N/A

N/A

06_7AH

8

Gemini Lake

1. Intel® Celeron® Processor J Series
2. Intel® Celeron® Processor N Series

N

N/A

N/A

06_7EH

5

Ice Lake U
Ice Lake Y

10th Generation Intel® Core™ Processor Family

Y

0xC2

N

06_86H

4

Snow Ridge BTS (Tremont)

Intel® Atom® Processors

N

N/A

N/A

06_86H

5

Snow Ridge BTS (Tremont)

Intel® Atom® Processor P5900

N

N/A

N/A

06_86H

7

Parker Ridge / Snow Ridge NS/NX/BTS

Intel Atom® Processor C5000
Intel Atom® Processor P5300
Intel® Atom® Processor P5700 Intel® Atom® Processor P5900

N

N/A

N/A

06_8CH

0,1

Tiger Lake U

11th Generation Intel® Core™ Processor Family

Y

0xB4

N

06_8CH

2

1. Tiger Lake U Refresh
2. Tiger Lake H35

11th Generation Intel® Core™ Processor Family

Y

0x34

N

06_8DH

0,1

Tiger Lake H

1. 11th Generation Intel® Core™ Processor Family
2. Intel® Xeon® Processor Family

Y

0x4E

N

06_8EH

9

1. Amber Lake-Y
2. Kaby Lake U
3. Kaby Lake U23e
4. Kaby Lake Y

1. 8th Generation Intel® Core™ Processor Family
2,3,4. 7th Generation Intel® Core™ Processor Family

N

N/A

N/A

06_8EH

A

1. Coffee Lake U43e
2. Kaby Lake Refresh U

8th Generation Intel® Core™ Processor Family

N

N/A

N/A

06_8EH

B

Whiskey Lake U

8th Generation Intel® Core™ Processors

N

N/A

N/A

06_8EH

C

1. Whiskey Lake U
2,3,4. Comet Lake U42
5. Amber Lake Y

1. 8th Generation Intel® Core™ Processors
2. 10th Generation Intel® Core™ Processor Family
3. Intel® Pentium® Gold Processor Series
4. Intel® Celeron® Processor 5000 Series
5. 10th Generation Intel® Core™ Processor Family

N

N/A

N

06_8FH

7, 8

Sapphire Rapids (Golden Cove)

4th Generation Intel® Xeon® Scalable processors                              
4th Generation Intel® Xeon® Platinum processors
4th Generation Intel® Xeon® Gold Processors
 4th Generation Intel® Xeon® Silver Processor
 4th Generation Intel® Xeon® Bronze Processor 
4th Gen Intel Xeon Scalable Processors with Intel® vRAN
Intel® Xeon® W workstation processors

Y

0x2B000461

N

06_8FH

7, 8

Sapphire Rapids (Golden Cove)

Intel® Xeon® CPU Max Series processors (High Bandwidth Memory HBM)

N

N/A

N

06_8FH

8

Sapphire Rapids Edge Enhanced LCC (Golden Cove)

5th Gen Intel Xeon Scalable Processors

N

N/A

0x2B000461 already in BIOS

06_96H

All

Elkhart Lake (Tremont)

Intel® Atom® Processors

N

N/A

N/A

06_97H

0,1,2,3,4

Alder Lake S (Golden Cove, Gracemont)

12th Generation Intel® Core™ Processor Family

Y

0x2b

N

06_97H

5

Alder Lake S (Golden Cove, Gracemont)

12th Generation Intel® Core™ Processor Family
Intel® Pentium® Gold Processor Family
Intel® Celeron® Processor Family

Y

0x2b

N

06_9AH

0,2,3

1. Alder Lake H (Golden Cove, Gracemont)
2. Alder Lake P (Golden Cove, Gracemont)

1. 12th Generation Intel® Core™ Processor Family
2. 12th Generation Intel® Core™ Processor Family

Y

0x428

N

06_9AH

4

Alder Lake U (Golden Cove, Gracemont)                     

12th Generation Intel® Core™ Processor Family
Intel® Pentium® Gold Processor Family
Intel® Celeron® Processor Family                     

Y

 0x428

N

06_9AH

4

Arizona Beach (Gracemont)

Intel® Atom® Processors

N

N/A

N

06_9CH

All

Jasper Lake (Tremont)

Intel® Atom® Processors

N

N/A

N/A

06_9EH

9

1. Kaby Lake S
2. Kaby Lake H
3. Kaby Lake G
4. Kaby Lake X
5. Kaby Lake Xeon E3

1. 7th Generation Intel® Core™ Processor Family
2. 7th Generation Intel® Core™ Processor Family
3. 8th Generation Intel® Core™ Processor Family
Intel® Pentium® Processor Family
4. Intel® Core™ X-series Processors
5. Intel® Xeon® E processor family

N

N/A

N/A

06_9EH

A

1. Coffee Lake H
2. Coffee Lake S Xeon E
3. Coffee Lake S x/KBP
4. Coffee Lake S

1. 8th Generation Intel® Core™ Processor Family
2. Intel® Xeon® E processor family
3. 8th Generation Intel® Core™ Processor Family
4. 8th Generation Intel® Core™ Processor Family

N

N/A

N/A

06_9EH

B

Coffee Lake S

1. 8th Generation Intel® Core™ Processor Family
2. Intel® Pentium® Gold Processor Series
3. Intel® Celeron® Processor G Series

N

N/A

N/A

06_9EH

C                

Coffee Lake S

9th Generation Intel® Core™ Processor Family

N

N/A

N/A

06_9EH

D

1. Coffee Lake H
2. Coffee Lake Xeon E
3. Coffee Lake S

1. 9th Generation Intel® Core™ Processor Family
2. Intel® Xeon® E processor family
3. 9th Generation Intel® Core™ Processor Family

N

N/A

N/A

06_A5H

0,1,2

Comet Lake H

10th Generation Intel® Core™ Processor Family
Intel® Xeon® W processor family

N

N/A

N/A

06_A5H

3

Comet Lake-S

10th Generation Intel® Core™ Processor Family
Intel® Pentium® Gold Processor Family
Intel® Celeron® Processor Family
Intel® Xeon® W processor family

N

N/A

N/A

06_A5H

5

Comet Lake-S

10th Generation Intel® Core™ Processor Family
Intel® Xeon® W processor family

N

N/A

N/A

06_A6H

All

Comet Lake U62

10th Generation Intel® Core™ Processor Family
Intel® Xeon® W processor family

N

N/A

N/A

06_A7H

All

Rocket Lake

1. 11th Generation Intel® Core™ Processor Family
2. Intel® Xeon® E-2300 processor family        
3. Intel® Xeon® W-1300 processor family

Y

0x5D

N

06_AAH

1

Meteor Lake (Redwood Cove, Crestmont)

 Intel® Core™ Ultra

N

N/A

N/A

06_B7H

1

Raptor Lake S (Raptor Cove/Gracemont)

13th Generation Intel® Core™ Processor Family      
Intel® Processor U-series

Y

0x112

N

06_B7H

1

Catlow (Raptor Cove)

 Intel® Xeon® E processor family

N

N/A

0x112 already in BIOS

06_BAH

2,3

Raptor Lake (Raptor Cove/Gracemont)

13th Generation Intel® Core™ Processor Family   
Intel® Processor U-series

Y

0x410E

N

06_BEH

0

Alder Lake N (Gracemont)

Intel® Core™ Processor N series
Intel® Processor N-series
Intel Atom® Processor X Series

N

N/A

N/A

06_BFH

2,5

Raptor Lake (Raptor Cove/Gracemont)

13th Generation Intel® Core™ Processor Family  
Intel® Processor U-series

Y

0x2B

N

06_CFH

2

Emerald Rapids (Raptor Cove)

5th Generation Intel® Xeon® Scalable processors  

N

N/A

N/A

 

Footnotes

  1. N/A = Not applicable because the processor is not affected.
  2. Some Apollo Lake processors have reached their End of Servicing Update (ESU) date. Please see our Support webpage for further information.

Product and Performance Information

1

Performance varies by use, configuration and other factors. Learn more at www.Intel.com/PerformanceIndex.