EUVD-2026-98832
GHSA-hwfh-h726-49f6
Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain
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AccessGain control of a guest domain
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ExploitIssue GNTTAB_cache_flush on system-domain page
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ExecutionRepeatedly leak page references exhausting host resources
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ImpactDenial of service of Dom0 or other domain
Vulnerability Assessment
| Weakness |
CWE
ASVS 5.0
V15 - Secure Coding and Architecture Resource release
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| Exploitation Conditions | Requires a running attacker-controlled guest domain on an x86 Xen host at version 4.5 through 4.20 able to issue GNTTAB_cache_flush grant-table hypercalls; the reference leak only manifests on the NULL-check error path (introduced by the XSA-232 fix) when the referenced page is owned by a special system domain, specifically DOM_IO or DOM_COW. Limiting factors that reduce realistic exposure: x86 only (Arm systems are not vulnerable), only versions 4.5-4.20 (4.21+ and 4.4 and earlier are unaffected), and the attacker must already hold guest-level control - there is no remote/network-only path. The advisory states there is no known mitigation other than applying the patch. |
| Impact | No CVSS vector, EPSS score, KEV listing, or POC was supplied in the input, so quantitative exploitation signals are entirely absent and real-world risk must be inferred from the vendor advisory alone. The Xen Security Team (XSA-520 v2) confirms the flaw is a page reference leak in GNTTAB_cache_flush handling whose most likely outcome is Denial of Service of Domain 0 (potentially the whole host) or of another guest domain - there is no indication of code execution, privilege escalation, or information disclosure. Exploitation requires an attacker to already control a guest domain on an affected x86 host and to drive the error path where the targeted page is owned by a special system domain (DOM_IO or DOM_COW), a non-trivial precondition rather than a trivial trigger. Net assessment: a genuine but bounded availability risk - meaningful for multi-tenant/hosting environments running Xen 4.5-4.20 with untrusted guests, but not a drop-everything issue given it is DoS-only, has no public exploit, and is not in CISA KEV. Note: no CVSS was published in the input, so any severity comparison is analyst-inferred and should be verified against official XSA-520 scoring. |
| Exploit ScenarioDerived | A malicious or compromised guest VM on an x86 Xen host (4.5-4.20) issues crafted GNTTAB_cache_flush grant-table hypercalls referencing a page owned by a special system domain (DOM_IO/DOM_COW), driving the error path that fails to drop a page reference. Repeated invocation leaks references so the page can never be freed, progressively starving host resources and causing denial of service of Domain 0 or another domain. No public exploit code was identified at time of analysis, and because the attack is a local hypercall from a guest it requires only a guest-level foothold, not network reachability. |
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Alert meAnalysisAIv1 – Oct 13, 2026
Page reference leaks in the Xen hypervisor's grant-table cache-flush handling (GNTTAB_cache_flush) allow an attacker who already controls a guest domain on an x86 host running Xen 4.5 through 4.20 to gradually exhaust host memory, most likely resulting in denial of service against Domain 0 (and therefore potentially the entire host) or against another domain. The defect sits on an error path that was added by the XSA-232 (CVE-2017-14318) NULL-pointer fix but never updated to release a page reference when the referenced page belongs to a special system domain such as DOM_IO or DOM_COW; per the vendor advisory there is no known mitigation other than applying the patch, and no public exploit identified at time of analysis. Authentication requirements are confirmed from the assessed vector (CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:N/I:N/A:H), which requires local guest-level privileges and a high degree of timing/conditions to trigger.
RemediationAI
Apply the vendor patch: XSA-520 provides xsa520.patch, which the advisory states resolves the issue and which is prepared against the Xen 4.20.x - 4.17.x stable branches, so downstreams should update to the tip of their stable branch before applying it to avoid context mismatches on release tarballs. The advisory explicitly states there is no known mitigation, so no configuration change, feature disable, or hypercall restriction is documented as an alternative; because the leak only manifests on the NULL-check error path when the referenced page is owned by DOM_IO or DOM_COW, minimising the number of pages assigned to those special system domains (for example reducing driver-domain/passthrough configurations that grant pages to the I/O domain) may lower the frequency of triggering, but this is an inference rather than a vendor-endorsed mitigation and carries operational trade-offs including loss of device passthrough and driver-domain functionality. Patching is the only reliable fix; until it is applied, exposure is bounded by the requirement that the attacker already controls a guest on an x86 host at version 4.5-4.20, so restricting guest creation to trusted tenants and monitoring host/Domain 0 memory consumption for unexplained growth are the practical compensating controls, with the caveat that neither stops a determined guest. Consult the Xen Project security policy page for embargo and disclosure handling context and the oss-security advisory for patch details.
Affected ProductsAI
Xen hypervisor versions 4.5 through 4.20 on x86 systems are affected; Xen 4.21 and newer, Xen 4.4 and older, and all Arm systems are explicitly not vulnerable. No CPE identifiers were supplied in the input data. The authoritative vendor advisory is XSA-520 / CVE-2026-102700, published to the oss-security list at https://seclists.org/oss-sec/2026/q4/148, with the Xen Project security process documented at http://www.xenproject.org/security-policy.html. The fix is distributed as the attached patch file xsa520.patch (SHA-256 e6814fe4a77d38f83c7bf3b92e8d24a0d95508572b845c622985e7021338cca9), which per the advisory applies to the Xen 4.20.x down to 4.17.x stable branches, with downstreams encouraged to update to the tip of the relevant stable branch before applying it.
Affects your stack
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Technical ContextAI · show details
Xen's grant table is the shared-memory mechanism through which a guest domain exposes pages to other domains or to the hypervisor, and GNTTAB_cache_flush is the hypercall that flushes cache state for such a grant. When XSA-232 (CVE-2017-14318) was fixed, a NULL pointer check was inserted into the cache-flush path, but the subsequent error branch was not adjusted: on that branch the hypervisor fails to drop the page reference it holds, leaking one reference to a page that is owned by a special system domain (DOM_IO or DOM_COW, system domains that can have memory pages assigned to them). This is a resource-lifetime/lifetime-management defect of the missing-reference-release class (the input assigns no CWE, so the classification is inferred from the described behaviour rather than from an assigned identifier). Because the leak is a reference count on a page rather than a direct memory corruption, there is no confidentiality or integrity impact; the effect is cumulative memory exhaustion. Vendor data restricts exposure to x86 (Arm is not vulnerable because the affected path and system-domain model are x86-specific) and to Xen 4.5 through 4.20, with 4.21 and newer and 4.4 and older unaffected, indicating the flaw was introduced with the original GNTTAB_cache_flush code and removed/refactored in later releases.
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Severity by source
AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
Guest-issued hypercall gives AV:L/PR:L; the leak requires the targeted page be owned by DOM_IO/DOM_COW, so AC:H; a guest impacts host/other domains (S:C) causing availability-only loss (A:H).
Primary rating from Vendor (CNA).
CVSS VectorVendor
Lifecycle Timeline
2Description PRE-NVD
Executive ViewAI
Organizations running the Xen hypervisor (versions 4.5 through 4.20) on x86 hosts face a high-severity denial-of-service risk from CVE-2026-102700. An authenticated attacker with local guest privileges can exploit a page reference leak to gradually exhaust host memory, potentially crashing Domain 0 and taking down the entire host. No public exploit identified at time of analysis, and no vendor-released patch identified at time of analysis; leadership should prioritize inventory and monitoring of affected hypervisors to protect critical services and multi-tenant environments.
No vendor-recommended mitigation exists other than applying the patch. Interim risk reduction measures include strict access control to guest domains (limiting who can create or manage guests), continuous monitoring of host memory consumption for signs of leakage, isolating critical workloads on separate hosts, and ensuring Domain 0 is not exposed to untrusted guests. Apply vendor patch as soon as it is released.
Threat Intelligence Overview
NVD
CVE.org
EPSS
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.
Exploit-DB