CVE-2026-102704 in Xen
Summary
by MITRE • 11/04/2026
[This CNA information record relates to multiple CVEs; the
text explains which aspects/vulnerabilities correspond to which CVE.]
A common access pattern is a batch of Grant Copy operations acting on adjacent address ranges in the same source or destination page. For performance reasons, Xen caches details internally to reuse already validated data. The conditions on when to re-validate the internal data were not correct in some cases:
- Frame numbers and grant references could wrongly be mixed up. This is CVE-2026-102703.
- Copying by frame number (rather than grant reference) is permitted only when operating on the caller's own memory. The check to enforce this restriction was misplaced. This is CVE-2026-102704.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 11/04/2026
The Xen hypervisor, a widely deployed Type 1 virtual machine monitor, contains critical logic errors within its implementation of the Grant Copy hypercall mechanism. These vulnerabilities stem from an optimization strategy designed to improve performance by caching validated data for batch operations acting on adjacent address ranges in the same source or destination page. While this caching reduces redundant validation overhead, the conditions governing when internal cached state must be re-validated were incorrectly defined. This flaw allows a malicious guest virtual machine to exploit inconsistencies between cached metadata and actual memory access permissions, leading to unauthorized information disclosure and potential privilege escalation within the hypervisor environment.
The first vulnerability, identified as CVE-2026-102703, involves a logic error where frame numbers and grant references are incorrectly mixed up during processing. In Xen's architecture, grant tables provide a secure mechanism for one domain to share memory with another by using reference identifiers rather than direct physical addresses. When the hypervisor processes batched copy operations, it relies on cached validation data to avoid re-checking permissions repeatedly. Due to the flawed condition checks, the system may erroneously treat a frame number as a valid grant reference or vice versa. This confusion bypasses the intended isolation boundaries because the security model for direct physical memory access differs significantly from that of cross-domain shared memory accessed via grants. An attacker can leverage this misidentification to read data they should not have access to, effectively violating confidentiality guarantees established by the hypervisor's security policy.
The second vulnerability, CVE-2026-102704, addresses a misplaced permission check regarding copying operations performed by frame number rather than grant reference. Xen strictly enforces that direct memory copies using physical frame numbers are permitted only when operating on the caller's own memory to prevent cross-domain data leakage or corruption. However, due to the incorrect placement of this validation logic within the code path handling batched operations, an unprivileged guest domain can bypass this restriction. By crafting specific sequences of hypercalls that exploit the caching mechanism and the misplaced check, a malicious VM can initiate copy operations targeting memory pages belonging to other domains or even hypervisor-owned structures. This represents a severe breach of isolation, allowing for unauthorized data exfiltration or potential code execution if writable targets are accessible.
From an industry standard perspective, these vulnerabilities align with CWE-20: Improper Input Validation and CWE-787: Out-of-bounds Write, as the core issue lies in failing to correctly validate input parameters against security constraints before acting on cached state. In terms of the MITRE ATT&CK framework for virtualization environments, these flaws facilitate techniques related to Defense Evasion by allowing a guest to bypass hypervisor-enforced boundaries and potentially Credential Access or Collection through unauthorized memory reads. The exploitation path typically involves crafting malicious hypercall arguments that trigger the specific code paths where validation is skipped due to the caching optimization, thereby exploiting the trust relationship between the guest OS and the Xen hypervisor without triggering standard security checks.
The operational impact of these vulnerabilities is significant for any infrastructure relying on Xen for virtualization services. Successful exploitation allows a compromised or maliciously constructed guest VM to read sensitive data from other guests, including cryptographic keys, session tokens, or proprietary application memory. Furthermore, if write operations can be manipulated through similar logic errors in related code paths, the attacker could corrupt critical system state, leading to denial of service for all virtual machines hosted on that physical host. This undermines the fundamental security guarantee of multi-tenant cloud environments where isolation between tenants is paramount.
Mitigation strategies primarily involve applying vendor-provided patches that correct the validation logic within the Xen grant table handling code. Administrators should ensure their hypervisor hosts are updated to versions that address CVE-2026-102703 and CVE-2026-102704 immediately upon availability. In environments where patching is not immediately feasible, implementing strict network segmentation between untrusted guest VMs can reduce the attack surface by limiting lateral movement opportunities if one domain is compromised. Additionally, enabling hardware-assisted virtualization features such as Intel VT-d or AMD-Vi with IOMMU enabled ensures that even if a guest attempts to access physical memory directly via frame numbers, the underlying hardware will block unauthorized DMA transactions and memory accesses, providing an additional layer of defense against exploitation of these logical flaws in the hypervisor software.