CVE-2025-26403: Intel Xeon 6 Privilege Escalation Flaw

CVE-2025-26403 is a privilege escalation vulnerability affecting Intel Xeon 6 processors using SGX or TDX. An out-of-bounds write flaw allows privileged users to escalate privileges locally. This article covers technical details, impact assessment, affected processor versions, and mitigation strategies.

CVE-2025-26403 Overview

CVE-2025-26403 is an out-of-bounds write vulnerability in the memory subsystem of certain Intel Xeon 6 processors. The flaw affects systems using Intel Software Guard Extensions (SGX) or Intel Trust Domain Extensions (TDX). A privileged local user can exploit the condition to potentially escalate privileges and compromise the confidentiality and integrity of protected enclaves and trust domains. The weakness is classified under [CWE-787: Out-of-bounds Write].

Critical Impact
A privileged local actor may break the isolation guarantees of Intel SGX enclaves and TDX trust domains on affected Xeon 6 platforms, undermining hardware-based confidential computing protections.

Affected Products

Select Intel Xeon 6 processors with Intel SGX enabled
Select Intel Xeon 6 processors with Intel TDX enabled
Debian systems shipping affected Intel microcode packages

Discovery Timeline

2025-08-12 - CVE-2025-26403 published to the National Vulnerability Database
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-26403

Vulnerability Analysis

The vulnerability resides in the memory subsystem logic that services Intel SGX enclaves and Intel TDX trust domains on affected Xeon 6 processors. Under specific conditions, the subsystem writes beyond an allocated memory boundary. The out-of-bounds write can corrupt adjacent state used by the trusted execution environment. This corruption can be leveraged by a privileged local user to alter execution and elevate privileges beyond the platform's confidential computing boundary. Exploitation requires high attack complexity and existing high privileges, which limits opportunistic abuse but does not eliminate risk in multi-tenant or confidential-computing deployments.

Root Cause

The issue is an out-of-bounds write [CWE-787] in the processor memory subsystem code paths invoked when SGX or TDX operations manipulate protected memory regions. Insufficient bounds enforcement allows a controlled write to cross the intended memory boundary. Because SGX and TDX are designed to isolate enclave and trust-domain state from privileged software, any write primitive reaching that state weakens the hardware root of trust.

Attack Vector

An attacker must already hold high privileges on the host, such as ring-0 kernel access or hypervisor-level control. From local access, the attacker triggers the vulnerable SGX or TDX code path to produce the out-of-bounds write. Network exploitation is not possible, and user interaction is not required. The primary risk scenario is a malicious or compromised operator attempting to break confidential-computing guarantees exposed to workload tenants.

No public proof-of-concept code is available for CVE-2025-26403. Refer to the Intel Security Advisory SA-01367 for authoritative technical details.

Detection Methods for CVE-2025-26403

Indicators of Compromise

Unexpected crashes, machine-check exceptions, or resets on Xeon 6 hosts running SGX or TDX workloads
Anomalous enclave attestation failures or TDX quote verification errors following privileged operations
Kernel or hypervisor log entries showing unusual SGX/TDX instruction faults (ENCLU, SEAMCALL, TDCALL)

Detection Strategies

Inventory Xeon 6 systems and cross-reference installed microcode revisions against the fixed versions listed in Intel SA-01367.
Monitor privileged process activity on hosts that run confidential workloads, focusing on kernel modules or hypervisor components that interact with SGX or TDX.
Track deployment of the Debian intel-microcode update referenced in the Debian LTS Announcement across the fleet.

Monitoring Recommendations

Alert on changes to microcode-loading services (microcode.ctl, intel-microcode) and on boot-time microcode revision mismatches.
Correlate SGX/TDX attestation failures with recent privileged access events to identify tampering attempts.
Baseline expected MSR reads/writes tied to SGX/TDX control registers and flag deviations from that baseline.

How to Mitigate CVE-2025-26403

Immediate Actions Required

Apply the Intel microcode update referenced in Intel Security Advisory SA-01367 to all affected Xeon 6 hosts.
On Debian systems, install the updated intel-microcode package per the Debian LTS Announcement.
Re-attest all SGX enclaves and TDX trust domains after patching to confirm platform integrity.

Patch Information

Intel has released microcode updates that address CVE-2025-26403. Consult Intel SA-01367 for the specific processor SKUs and microcode revisions. Linux distributions are shipping the fix through their microcode packages; Debian LTS has published a corresponding advisory. Cloud and hypervisor vendors typically deliver the update through host BIOS/UEFI firmware or operating system microcode loaders.

Workarounds

Restrict host-level privileged access to trusted administrators until microcode updates are deployed.
Where feasible, disable SGX and TDX on affected Xeon 6 hosts that do not require confidential computing until patched.
Isolate confidential workloads onto hosts that have received the Intel microcode fix and enforce attestation before scheduling sensitive tenants.

bash

# Verify installed Intel microcode revision on Linux
grep -m1 'microcode' /proc/cpuinfo

# Debian: install the fixed intel-microcode package
sudo apt update && sudo apt install --only-upgrade intel-microcode

# Reboot to load the new microcode, then re-check
sudo reboot