CVE-2023-23583: Intel Core i3-10100Y Privilege Escalation

CVE-2023-23583 Overview

CVE-2023-23583, publicly known as Reptar, affects a wide range of Intel processors including 10th, 11th, 12th, and 13th generation Core CPUs and multiple Xeon Scalable and Xeon D families. A specific sequence of processor instructions involving redundant REX prefixes can trigger unpredictable system behavior. An authenticated local user can exploit this condition to escalate privileges, disclose sensitive information, or cause denial of service. The flaw is mapped to CWE-1281: Sequence of Processor Instructions Leads to Unexpected Behavior and [CWE-276: Incorrect Default Permissions].

Critical Impact
An authenticated local attacker can break virtual machine isolation, leak data across security boundaries, or crash hypervisor hosts running affected Intel silicon.

Affected Products

Intel Core processors (10th, 11th generations including Ice Lake, Tiger Lake, Rocket Lake)
Intel Xeon D-1500/D-1600/D-1700/D-2100/D-2700/D-2800 series and Xeon Scalable (Ice Lake-SP) processors
Debian GNU/Linux 11 and 12, plus NetApp FAS2820, AFF A900, and FAS9500 storage systems

Discovery Timeline

2023-11-14 - CVE-2023-23583 published to NVD with coordinated advisory release
2023-11-14 - Intel publishes Intel Security Advisory SA-00950 and microcode update
2023-11-16 - NetApp publishes advisory NTAP-20231116-0015
2023-12 - Debian releases DSA-5563 with updated intel-microcode packages
2025-01-07 - Last updated in NVD database

Technical Details for CVE-2023-23583

Vulnerability Analysis

The Reptar flaw resides in how affected Intel CPUs decode and execute instructions that include redundant REX prefixes, particularly when combined with fast short repeat move (FSRM) instructions such as rep movsb. Under specific conditions, the processor enters an undefined microarchitectural state. This state can corrupt control flow, leak architectural register contents, or hang the core entirely. Because the bug triggers below the operating system layer, traditional kernel-level isolation cannot contain it. An unprivileged guest in a virtualized environment can use the instruction sequence to crash the host or read data belonging to other tenants. Researchers also demonstrated that the condition can produce inconsistent state across hyperthreads sharing a physical core.

Root Cause

The defect originates in the CPU's instruction decode and microcode handling of redundant prefix bytes. Specifications require these prefixes to be ignored, but affected silicon mishandles the resulting microoperations when paired with branch and repeat-move instructions. This violates the architectural contract between user code and the processor, mapping to [CWE-1281].

Attack Vector

Exploitation requires local code execution on a vulnerable host, but no elevated privileges. A standard user, a container process, or an unprivileged VM guest can construct the trigger sequence. The proof-of-concept released alongside the Openwall disclosure consists of a short assembly block that issues rep movsb with crafted REX prefixes inside a tight loop. Successful triggering produces machine check exceptions, register corruption, or system hangs.

// Conceptual trigger pattern - see Openwall advisory for full details
// rex.W + rex.W + rep movsb under specific branch conditions
// causes the CPU to enter an undefined microarchitectural state

Detection Methods for CVE-2023-23583

Indicators of Compromise

Unexpected #MC (Machine Check) exceptions logged in mcelog, dmesg, or Windows WHEA event logs without correlated hardware failures
Unscheduled VM guest crashes, hypervisor host hangs, or kernel panics with general protection faults referencing unusual instruction pointers
Processes generating sustained tight loops of rep movsb with redundant REX prefix patterns visible in instruction tracing

Detection Strategies

Inventory CPU models against the Intel SA-00950 affected list and confirm running microcode revision via /proc/cpuinfo (Linux) or Get-WmiObject Win32_Processor (Windows)
Monitor endpoint telemetry for unsigned binaries that execute inline assembly or load JIT-generated code containing repeated 0x40-0x4F prefix bytes before string operations
Correlate hypervisor host stability events with guest workload identity to surface tenants attempting trigger sequences

Monitoring Recommendations

Forward kernel ring buffer, MCE, and hypervisor crash dumps to a centralized analytics platform for cross-host correlation
Track microcode version drift across the fleet and alert when hosts fall behind the SA-00950 baseline
Baseline normal rep movsb usage in production workloads to flag anomalous instruction sequences originating from non-system processes

How to Mitigate CVE-2023-23583

Immediate Actions Required

Apply the Intel microcode update referenced in Intel SA-00950 through OS vendor packages or BIOS/UEFI firmware updates from the hardware OEM
Update Debian systems using DSA-5563 and the corresponding Debian LTS advisory to install the patched intel-microcode package
For NetApp customers, follow remediation in NTAP-20231116-0015 for FAS2820, AFF A900, and FAS9500
Reboot systems after microcode deployment so the updated patch loads at boot

Patch Information

Intel released microcode revision IPU 2023.3 addressing the redundant prefix decoding fault. Linux distributions shipped this microcode through their intel-microcode packages. Cloud providers including AWS, Azure, and GCP rolled out hypervisor-level mitigations on their managed fleets. Verify deployment using dmesg | grep microcode to confirm the new revision is loaded.

Workarounds

Restrict local code execution on multi-tenant hosts by enforcing strict container runtime policies and disallowing unprivileged JIT compilation where feasible
On systems that cannot receive microcode updates, isolate untrusted workloads on dedicated non-affected hardware until firmware can be applied
Disable shared hyperthreading for sensitive workloads to reduce cross-thread impact while patching is in progress

bash

# Verify loaded microcode revision on Linux
grep microcode /proc/cpuinfo | head -1
dmesg | grep -i microcode

# Debian/Ubuntu - apply patched microcode
sudo apt update && sudo apt install --only-upgrade intel-microcode
sudo update-initramfs -u
sudo reboot