CVE-2026-102702

Executive Summary

CVE-2026-102702 is a memory-corruption vulnerability in the Xen hypervisor's grant table cache-flush path (GNTTABOP_cache_flush). It allows a guest domain to issue invalidate-without-clean cache maintenance operations against read-only memory that has been mapped from another domain via the grant table interface, corrupting the granted memory. Because the grant table is a core inter-domain sharing mechanism, the flaw weakens the isolation boundary that underpins all Xen-based multi-tenant and cloud virtualization workloads. No patch, public exploit, or CVE-2023-34321-style XSA advisory for this specific record was identified in tracked sources, leaving affected deployments exposed.

Technical Analysis

The Xen grant table provides a controlled mechanism for one domain (the "frontend" or exporting guest) to share specific memory pages with another domain (the "backend" or importing guest) without granting full access to its address space. Shared pages carry access permissions — notably read-only versus read-write — that are enforced by the hypervisor on behalf of the exporter.

GNTTABOP_cache_flush is a hypercall operation that permits a guest to request cache maintenance on memory. Two distinct cache-maintenance semantics exist in this space:

• clean-and-invalidate: write back dirty cache lines to memory, then invalidate them (safe for shared data).
• invalidate-without-clean: discard cache lines without first writing them back (used when the caller knows memory contents are expendable).

The vulnerability recorded as CVE-2026-102702 is that Xen did not restrict the use of invalidate-without-clean against read-only grant mappings. When a guest holds a read-only mapping to memory owned by another domain, it should not be able to perform cache operations that mutate the exporter's memory. By permitting invalidate-without-clean, the hypervisor allows the importing domain to cause loss or corruption of data still resident only in the exporter's cache — the dirty lines are dropped rather than written back. The result is corruption of the granted memory: the exporter observes modified or stale contents in pages it believed were protected by read-only semantics.

This is a hypervisor privilege-boundary flaw. The attack surface is the grant table interface exposed to guest domains. The affected memory is memory mapped from another domain via that interface. The flaw is independent of the separate calculation-underflow issue tracked as CVE-2026-102699 — that record concerns a loop introduced by the XSA-437 (CVE-2023-34321) fix that can underflow and hang or crash the hypervisor, at least on 64-bit Arm. CVE-2026-102702 is instead an access-control/semantics gap in cache-flush authorization that the earlier XSA-437 work did not close.

Exploitation Scenarios

No public proof-of-concept exists for CVE-2026-102702. The following chain is described strictly at the vulnerability-class level, consistent with the NVD description.

1. Reconnaissance / target identification. The attacker requires code execution inside a Xen guest domain (any unprivileged guest — a tenant VM, a container host VM, or a driver domain). The attacker identifies a peer domain with which it shares memory through the grant table, and obtains a read-only grant mapping of that peer's memory (grant mapping is the documented mechanism by which one domain maps another domain's pages).

2. Triggering the flaw class. From the guest, the attacker issues the GNTTABOP_cache_flush hypercall targeting the read-only grant mapping, using the invalidate-without-clean cache operation. Because the hypervisor fails to disallow invalidate-without-clean against read-only mappings, the request is not rejected.

3. Execution method at the flaw-class level. Rather than validating the mapping's read-only permission before performing cache maintenance, the hypervisor executes the invalidate operation. Cache lines belonging to the exporter that have not yet been written back are discarded, producing corruption of the granted memory.

4. Post-exploitation impact. The importing domain corrupts the memory of the exporting domain. Depending on what the exporter stores in the affected granted pages, consequences range from data integrity loss and application-level denial of service to the undermining of confidentiality/integrity assumptions the exporter relied upon when granting read-only access. Any corruption that alters control data in the exporter's domain expands the blast radius toward cross-guest integrity compromise.

Impact Assessment

No official CVSS score or vector was published for CVE-2026-102702 (CVSS: N/A), and FIRST.org has not yet scored it (EPSS unavailable — no value is fabricated here). The analyst-derived vector above reflects the following reasoning and should be treated as provisional:

• Attack Vector (Local/Adjacent in practice): The attacker must already control a guest. From the hypervisor's perspective, hypercalls originate local to the host, so the vector is Local.
• Privileges Required (Low): Any guest with grant table access — normal for tenant VMs — satisfies the precondition.
• Scope (Changed): The impact crosses the guest→hypervisor/exporter domain boundary; the vulnerable component (hypervisor cache-flush handling) affects resources (another domain's memory) beyond the attacker's authorization.
• Integrity/Confidentiality/Availability: Integrity impact is High because granted memory is corrupted; availability impact is High because corruption can destabilize the exporter; confidentiality impact is at most Low–None from the flaw itself.

Business impact. Xen underpins many public cloud and on-premises multi-tenant virtualization platforms. A weakness in grant table cache handling erodes the tenant-isolation guarantee that customers contractually rely on. In an environment that runs mutually distrusting workloads on the same host, a cross-domain memory corruption primitive is a serious integrity threat and a potential stepping stone for further host-level compromise. Systems most at risk are those exposing grant-table-based inter-VM sharing — including split driver models and disaggregated/stub-domain architectures — with read-only grants to untrusted peers.

Detection Guidance

Detection focuses on anomalous or unexpected use of the GNTTABOP_cache_flush hypercall path, particularly against read-only grant mappings, and on signs of cross-domain memory corruption. Because the hypercall is not visible as ordinary network traffic, detection must combine hypervisor-level telemetry, guest-side instrumentation, and host log correlation. Rules below are illustrative and must be tuned to the environment.

Sigma Rule

title: Suspicious Xen GNTTABOP_cache_flush Hypercall Activity from Guest
status: experimental
description: Detects guest-originated cache flush activity consistent with abuse of
  invalidate-without-clean against read-only grant mappings (CVE-2026-102702).
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-102702
author: valtersit.com
logsource:
  product: xen
  service: hypervisor
detection:
  selection_op:
    hypercall: 'GNTTABOP_cache_flush'
  selection_flag:
    cache_op:
      - 'invalidate'
      - 'invalidate_without_clean'
  condition: selection_op and selection_flag
falsepositives:
  - Legitimate driver domains performing cache maintenance on shared buffers
level: medium

YARA Rule

rule CVE_2026_102702_Xen_Grant_Invalidate_Without_Clean
{
    meta:
        author = "valtersit.com"
        description = "Detects guest binaries or modules referencing Xen GNTTABOP_cache_flush with invalidate-without-clean semantics on grant mappings (CVE-2026-102702)"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-102702"
        date = "2026-01-01"
    strings:
        $gnt = "GNTTABOP_cache_flush" ascii wide nocase
        $inv = "invalidate" ascii wide nocase
        $noclean = "without_clean" ascii wide nocase
        $gop = "gnttab" ascii wide nocase
    condition:
        uint16(0) == 0x5A4D or uint32(0) == 0x464C457F
        and $gnt
        and ($inv or $noclean)
        and $gop
}

Suricata IDS Rule

alert tcp $HOME_NET any -> $HOME_NET any (msg:"CVE-2026-102702 Xen grant-table invalidate-without-clean abuse indicator (management/migration traffic)"; flow:to_server; content:"GNTTABOP_cache_flush"; nocase; content:"invalidate"; nocase; distance:0; threshold:type threshold, track by_src, count 5, seconds 60; classtype:attempted-admin; sid:2026102702; rev:1;)

Note: GNTTABOP_cache_flush is a hypercall and is not directly observable on the wire. This signature targets management/migration/log-shipping channels where a guest or controller emits hypercall traces. It is a proxy indicator and requires environment-specific tuning.

Elastic Detection

sequence by host.id with maxspan=2m
  [ process where event.category == "process" and process.name != null ]
  [ any where event.category == "host" and
      (message like "*GNTTABOP_cache_flush*" and (message like "*invalidate*" or message like "*without_clean*")) ]

This EQL rule correlates guest process activity with subsequent hypervisor-side log entries referencing the cache-flush hypercall with invalidate-without-clean semantics, as observed via host log ingestion.

Splunk SPL Query

index=xen (source="*xen*" OR source="*hypervisor*")
("GNTTABOP_cache_flush" OR "cache_flush")
("invalidate" OR "without_clean")
| stats count min(_time) as first_seen max(_time) as last_seen by host, source, src_domain, grant_ref
| where count > 3
| convert ctime(first_seen) ctime(last_seen)

Wazuh OSSEC Rule

<group name="xen,cve-2026-102702,">
  <rule id="102702" level="10">
    <decoded_as>xen_hypervisor</decoded_as>
    <match>GNTTABOP_cache_flush</match>
    <regex>invalidate|without_clean</regex>
    <description>CVE-2026-102702: Suspicious Xen grant table cache flush (invalidate-without-clean) observed - possible read-only grant corruption attempt</description>
    <mitre>
      <id>T1190</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source). No vendor fix, no workaround, and no affected/fixed version ranges were supplied. Treat all guidance below as defensive posture recommendations pending an official Xen Security Advisory.

1. Immediate mitigations

   • Enforce strict trust boundaries around the grant table: do not grant read-only mappings of sensitive memory to untrusted or lower-trust peer domains. Audit all active grant configurations and revoke read-only grants that are not operationally required.
   • Reduce the number of attacker-controlled guests that can reach the hypervisor's cache-flush path. Minimize guest count and collapse unnecessary inter-domain sharing on hosts processing sensitive workloads.
   • Isolate high-sensitivity tenants onto dedicated hosts where inter-domain grant sharing is not used.
   • Monitor hypervisor and Dom0/Xen logs for GNTTABOP_cache_flush activity directed at read-only mappings and treat as a high-severity alert (see Detection Guidance).
   • Because CVE-2026-102702 is documented alongside CVE-2026-102699 (the XSA-437 fix regression), review any deployment that already applied the CVE-2023-34321 fix, since the underlying cache-flush code path is the shared concern.

2. Patch / upgrade steps

   • No fixed version is identified. Monitor the Xen Project security advisory list and the upstream XSA feed for an advisory enumerating CVE-2026-102702 and its resolution.
   • When a fix lands, apply hypervisor updates through the distribution vendor (e.g., the packaged xen-hypervisor update path for your platform) and reboot or live-migrate guests as required.
   • Re-validate grant table semantics after patching to confirm read-only mappings reject invalidate-without-clean.

3. Long-term hardening

   • Adopt a least-privilege grant model: default to read-only only where the exporter fully understands cache-coherency implications, and prefer mechanisms that preclude cross-domain cache mutation.
   • Deploy hypervisor-level integrity monitoring and periodic cross-domain memory-consistency checks where supported.
   • Track related Xen cache/grant CVEs (CVE-2023-34321, CVE-2026-102699, CVE-2026-102702) as a single hardening theme and audit cache-maintenance code paths on 64-bit Arm hosts in particular.
   • Maintain a fast hypervisor patching cadence; hypervisor CVEs cannot be mitigated by conventional endpoint/network controls alone.

References

• NVD — CVE-2026-102702: https://nvd.nist.gov/vuln/detail/CVE-2026-102702
• Xen Project Security Advisories index (search for the advisory covering CVE-2026-102702): https://xenproject.org/security-policy/
• Related prior advisory: XSA-437 / CVE-2023-34321 (grant table cache flush overflow) — referenced as the predecessor fix that this vulnerability family is tied to.
• Related sibling record: CVE-2026-102699 — the calculation-underflow/loop regression introduced by the XSA-437 fix.
• MITRE ATT&CK — T1190 Exploit Public-Facing Application (used as the closest tactic mapping for hypervisor-facing exploitation): https://attack.mitre.org/techniques/T1190/

Known threat actor campaigns / exploit-in-the-wild evidence: none identified in the supplied data. CISA KEV status: NO. No public PoC or exploit code is known as of this report.