CVE-2025-31936

Executive Summary

CVE-2025-31936 is a privilege escalation vulnerability affecting some Intel Xeon 6 processors when Intel TDX (Trust Domain Extensions) is used within SMM (System Management Mode). Improper handling of overlap between protected memory ranges allows an adversary already positioned in SMM — combined with a privileged user context — to compromise the confidentiality and integrity of TDX-protected memory via local access. As of this report, no patch, vendor advisory, or public PoC has been identified; the vulnerability is classified as unpatched with a low EPSS score (0.00096).

Technical Analysis

The flaw is rooted in CWE-1260: Improper Handling of Overlap Between Protected Memory Ranges. Intel TDX provides hardware-enforced isolation for confidential computing workloads (trust domains) on Xeon 6 processors, while SMM is a highly privileged x86 execution mode (CPU privilege level below the OS kernel). The NVD description states that improper handling of the overlap between protected memory ranges on affected processors creates a condition under which an SMM adversary — who additionally holds a privileged user context — can escalate privilege.

The attack surface is strictly local. The description characterizes the attack as high complexity, requiring attack conditions to be present along with "special internal knowledge," and requiring no user interaction. The affected component's confidentiality and integrity impact are both rated High; availability impact on the vulnerable system is None. The description further states that "subsequent system" confidentiality, integrity, and availability impacts are all None, indicating the compromise is contained to the SMM/TDX memory protection boundary rather than cascading into other system components.

No code-level details are available: the CNA title is empty, no vendor advisory has been published, and the NVD description does not enumerate specific instructions, registers, memory layout constants, or firmware components. Per analysis constraints, this report does not fabricate implementation specifics. At the vulnerability-class level, the mechism is a memory-protection bypass: overlapping address ranges between SMM-resident firmware memory and TDX-protected memory are not disambiguated correctly, allowing an SMM actor to read or modify memory that should be isolated within a trust domain.

It is important to interpret the privilege model correctly. The adversary is characterized as an "SMM adversary" — i.e., the attacker already possesses code execution within System Management Mode — combined with a privileged user. The escalation therefore is not a conventional user-to-root bug but an intra-privilege-layer break of TDX's confidentiality and integrity guarantees from an SMM vantage point. This is consistent with the formal security goal of TDX, which assumes SMM is not a trusted component; this vulnerability invalidates that assumption on affected Xeon 6 parts.

Exploitation Scenarios

No public PoC is available; the attack chain below is inferred strictly from the vulnerability class (CWE-1260) and the NVD description. No specific function names, file paths, or API endpoints are disclosed in the source data, and none are invented here.

1. Reconnaissance / target identification. The attacker first identifies a target running affected Intel Xeon 6 processors with Intel TDX enabled and SMM accessible. Because the attack requires "special internal knowledge" and a privileged user context, reconnaissance focuses on understanding the target's firmware configuration, TDX metadata layout, and the address ranges reserved for SMM versus trust domain memory. The attacker must already have (or have achieved) SMM code execution and a privileged user account — meaning the target environment is already partially compromised.

2. Triggering the flaw. At the vulnerability-class level, the attacker manipulates the processor's handling of overlapping protected memory ranges. By intentionally configuring or corrupting descriptors for SMM-reserved memory and TDX-protected memory so that the ranges overlap, the attacker causes the CPU's isolation logic to grant SMM access to memory that TDX is designed to protect. The high-complexity rating and the requirement for internal knowledge reflect the precision needed to control these ranges without triggering a platform fault.

3. Payload/execution. Execution occurs within SMM, with no user-interaction requirement. A class-level payload would consist of SMM-resident code that reads or writes the overlapping protected range, thereby accessing trust domain memory or modifying TDX protection metadata. The payload is executed at SMM privilege and persists within the firmware execution context; no network vector exists for this CVE.

4. Post-exploitation impact. A successful pass compromises the confidentiality and integrity of TDX-protected workloads. An SMM actor can exfiltrate TDX guest memory or tamper with its contents, undermining the trust boundary that confidential computing tenants rely on. Availability impact is absent from the vulnerable component, and no downstream systems are affected per the description. The practical business consequence is a full break of TDX's hardware-rooted isolation on the affected host, with the operator unable to detect the compromise from inside the guest or the hypervisor.

Impact Assessment

• Business impact: High. The vulnerability defeats the core security guarantee of Intel TDX on Xeon 6 — isolation of confidential workloads from the platform firmware and the host OS. Any organization running TDX-based confidential computing (multi-tenant cloud providers, regulated industries, secure enclave hosting) must treat a successful exploitation as a total loss of trust-domain confidentiality and integrity on the affected physical host.
• Affected systems: Some Intel Xeon 6 processors using Intel TDX within SMM. Exact SKUs, steppings, and microcode versions are not disclosed in the available data; affected version data is marked empty.
• Blast radius: Local only. There is no network attack surface. The attacker must already hold SMM code execution and a privileged user context — a high bar that filters out most opportunistic attackers. However, for environments already penetrated at the firmware/admin level, the impact is total with respect to TDX-protected data.
• Likelihood: EPSS 0.00096 (0.8th percentile of exploited CVEs) and no inclusion in CISA KEV indicate that exploitation in the wild is not currently observed. The high complexity, special-knowledge requirement, and need for SMM access further suppress near-term likelihood. Severity, however, is driven by impact: High/High confidentiality/integrity within the vulnerable component.
• Note: CVSS score and vector are not assigned (N/A), so quantitative severity comparison is not possible; this report does not override the absence of a vector.

Detection Guidance

The following detections are best-effort, vulnerability-class-level controls. CVE-2025-31936 is a local, processor/firmware-level flaw; there is no network exploit payload and no public exploit artifact. The pre-exploitation phase involves an already-privileged actor loading or executing tooling that references TDX/SMM constructs or performs kernel-module operations. Rules below target those observable prerequisites and post-exploitation behaviors on Linux hosts (the predominant platform for TDX), with one network rule for administrative sessions toward TDX-enabled assets. Tune threshold rules to local host inventories.

Sigma Rule

title: CVE-2025-31936 TDX SMM Privilege Escalation Prerequisite Activity
id: f44b2b18-0000-4000-8000-2025319360
status: experimental
description: >
  Detects kernel module loading or kexec operations whose command line references
  Intel TDX or SMM constructs on Linux hosts. Such activity is a plausible
  prerequisite for exercising CVE-2025-31936 (improper handling of protected
  memory range overlap in Intel Xeon 6 TDX/SMM) by an actor with privileged access.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2025-31936
author: Valters IT Threat Intelligence
date: 2026/05/07
logsource:
  category: process_creation
  product: linux
detection:
  selection_cmd:
    Image|endswith:
      - '/insmod'
      - '/modprobe'
      - '/kexec'
  selection_args:
    CommandLine|contains|all:
      - 'tdx'
      - 'smm'
  condition: selection_cmd and selection_args
falsepositives:
  - Legitimate TDX provisioning and platform administration tooling
  - Firmware update automation referencing the TDX module
level: high
tags:
  - attack.privilege_escalation
  - attack.t1068
  - cve.2025.31936

YARA Rule

rule CVE_2025_31936_TDX_SMM_Tooling_Hunt
{
    meta:
        author = "Valters IT Threat Intelligence"
        description = "Hunts for PE or ELF binaries and memory dumps that reference Intel TDX and SMM constructs associated with CVE-2025-31936 activity."
        cve = "2025-31936"
        cwe = "CWE-1260"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-31936"
        date = "2026-05-07"
    strings:
        $s1 = "tdx" ascii wide nocase
        $s2 = "smm" ascii wide nocase
        $s3 = "trust domain" ascii wide nocase
        $s4 = "system management mode" ascii wide nocase
    condition:
        // PE file
        (uint16(0) == 0x5A4D and uint32(uint32(0x3C)) == 0x00004550)
        or
        // ELF file
        (uint32(0) == 0x464C457F)
    and
        ($s1 or $s3) and ($s2 or $s4) and filesize < 10MB
}

Note: This is a hunting rule, not a signature for a known malicious artifact. No public PoC or exploit sample exists to fingerprint, so the rule flags tooling that discusses/operates at the affected abstraction level. Tune against legitimate Intel provisioning utilities and expect noise on developer/test hosts.

Suricata IDS Rule

CVE-2025-31936 is a local processor-level vulnerability and cannot be exploited over the network. No valid network signature exists. The rule below is a compensating control that flags administrative SMB sessions toward hosts in a $TDX_ENABLED_HOSTS asset list; such sessions are a common delivery path for the privileged-user stage that precedes SMM-level exploitation. Customize the variable and treat alerts as enrichment, not direct indicators of exploitation.

# CVE-2025-31936 - compensating network detection
# Vulnerability class: local SMM/TDX protected-memory-overlap privilege escalation (Intel Xeon 6).
# There is no network exploit payload; this rule detects administrative SMB sessions
# toward TDX-enabled assets, a plausible precursor to local privileged activity.
alert tcp any any -> $TDX_ENABLED_HOSTS 445 (msg:"CVE-2025-31936 Potential Administrative SMB Session Toward TDX Host"; flow:established,to_server; content:"|fe 53 4d 42|"; depth:4; reference:cve,2025-31936; classtype:attempted-admin; sid:2025319360; rev:1;)

Elastic Detection

// EQL — Linux auditd integration, kernel-module load referencing TDX/SMM.
sequence by host.id with maxspan=10m
  [ process where event.action == "start" and event.module == "auditd"
      and process.name in ("insmod", "modprobe", "kexec") ]
  [ file where event.action in ("write", "create")
      and file.extension in ("ko", "o") ]

// EQL — process-level hunt for TDX/SMM tooling execution by privileged users.
any where process.command_line : ("*tdx*", "*smm*", "*trust domain*") and
  process.user.name in ("root", "SYSTEM") and
  process.name in ("insmod", "modprobe", "kexec", "bash", "sh", "powershell.exe", "cmd.exe")

Splunk SPL Query

index=linux sourcetype=linux_audit
  (syscall=init_module OR syscall=finit_module OR syscall=execve)
  (ARGS=*tdx* OR ARGS=*smm* OR process=*tdx* OR process=*smm*)
| stats count min(_time) as earliest max(_time) as latest by host, user, process, ARGS
| where count > 0

// Correlate with local privilege escalation: audit success for privileged account use
// on hosts identified as Intel Xeon 6 / TDX-enabled (populate the asset list).
index=linux sourcetype=linux_audit (SYSCALL=init_module OR SYSCALL=finit_module)
| eval module_key = host . "_" . user
| stats values(ARGS) as module_args dc(ARGS) as arg_diversity by host, user
| where arg_diversity > 0

Wazuh OSSEC Rule

<group name="cve-2025-31936,">
  <rule id="100345" level="12">
    <decoded_as>auditd</decoded_as>
    <field name="syscall">init_module|finit_module</field>
    <regex>tdx|smm</regex>
    <description>CVE-2025-31936: kernel module load referencing TDX/SMM detected on Intel Xeon 6 host (potential protected-memory-overlap exploitation precursor)</description>
    <mitre>
      <id>T1068</id>
    </mitre>
    <group>privilege_escalation,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence is 0/4 (UNPATCHED): no patch, microcode update, or firmware fix is available from any tracked source at the time of writing. The vendor fix field is N/A and no workarounds are documented.

1. Immediate mitigations (until firmware/patch availability):

• Restrict and audit privileged user accounts on TDX-enabled Xeon 6 hosts. Since the attack requires a privileged user combined with an SMM adversary, reducing the population of administrators with local shell access materially shrinks the attack surface.
• Disable Intel TDX on hosts where confidential-computing isolation is not an active business requirement. If TDX workloads are not running, the vulnerable configuration is avoidable.
• Apply vendor-recommended SMM/BIOS security settings (e.g., SMM write-protection and secure SMM mitigation controls offered in platform firmware menus) where available for Xeon 6 platforms.
• Treat all SMM-capable firmware (BIOS/UEFI, BMC) as part of the trusted computing base; ensure firmware update signing and secure-boot chains are enforced.

2. Patch/upgrade steps:

• No patch exists. Subscribe to Intel PSIRT notifications and the Intel Product Security Center for an advisory referencing CVE-2025-31936 (expected deliverables: CPU microcode, platform firmware update, or an updated SMM/TDX reference code entitlement).
• Validate TDX firmware and microcode versions against Intel's published CPUID/version enumeration for Xeon 6 before and after deployment.
• Re-test TDX attestation reports after any platform firmware change to confirm the security properties advertised to tenants.

3. Long-term hardening:

• Enforce separation of duties between platform administrators (who can reach SMM) and TDX workload tenants; consider dedicated management-plane hosts that never run guest workloads.
• Deploy attestation and runtime-integrity monitoring for TDX trust domains so that a silent confidentiality/integrity break can be detected by tenants through quote verification failures.
• Implement privileged access management (PAM), MFA, and session recording for all privileged user sessions on Xeon 6 hosts; forward auditd/Wazuh events per the detection guidance above.
• Track CISA KEV and EPSS updates for this CVE; revisit priority as new microcode availability changes the risk calculation.

References

1. NVD — CVE-2025-31936: https://nvd.nist.gov/vuln/detail/CVE-2025-31936
2. MITRE CWE-1260 (Improper Handling of Overlap Between Protected Memory Ranges): https://cwe.mitre.org/data/definitions/1260.html
3. Intel Product Security Center (monitor for future advisory): https://www.intel.com/content/www/us/en/security-center/default.html
4. CISA Known Exploited Vulnerabilities Catalog (currently NOT listed): https://www.cisa.gov/known-exploited-vulnerabilities-catalog
5. FIRST EPSS (score 0.00096, 0.8th percentile): https://www.first.org/epss/

Threat-actor campaign evidence: none identified. No exploit-in-the-wild reporting, CISA KEV inclusion, or public PoC exists for CVE-2025-31936 as of this report. The attack chain described above is inferred from the vulnerability class (CWE-1260) and the NVD description; specific technical details (registers, memory ranges, firmware components) remain unavailable pending vendor disclosure.