Xen
CVE-2021-28696
MEDIUM
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A01:2025 - Broken Access Control
ASVS 5.0
V8 - Authorization Authorization logic validation
MITRE ATT&CK
1 technique across 1 tactic: Privilege Escalation The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. |
| Impact | CVSS score of 6.8 (MEDIUM). Attack characteristics: physical attack vector, low complexity, no privileges required, no user interaction not required. |
| Exploit ScenarioDerived | An attacker could exploit this vulnerability to bypass authorization checks to access restricted resources. No authentication is required to exploit this vulnerability. |
Get an e-mail when this CVE is exploited, patched or re-scored. Free account.
Alert meAnalysisAI
IOMMU page mapping issues on x86 T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Both AMD and Intel allow ACPI tables. Rated medium severity (CVSS 6.8), this vulnerability is no authentication required, low attack complexity. No vendor patch available.
RemediationAI
No vendor patch is available at time of analysis. Monitor vendor advisories for updates. Review and test authorization logic, implement consistent access control checks, use centralized authorization framework.
Affects your stack
Find out whether the stacks and servers you run are on an affected version.
Checking this CVE against your own stacks and servers is part of the Basic plan and up.
Technical ContextAI · show details
This vulnerability is classified as Incorrect Authorization (CWE-863), which allows attackers to bypass authorization checks to access restricted resources. IOMMU page mapping issues on x86 T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Both AMD and Intel allow ACPI tables to specify regions of memory which should be left untranslated, which typically means these addresses should pass the translation phase unaltered. While these are typically device specific ACPI properties, they can also be specified to apply to a range of devices, or even all devices. On all systems with such regions Xen failed to prevent guests from undoing/replacing such mappings (CVE-2021-28694). On AMD systems, where a discontinuous range is specified by firmware, the supposedly-excluded middle range will also be identity-mapped (CVE-2021-28695). Further, on AMD systems, upon de-assigment of a physical device from a guest, the identity mappings would be left in place, allowing a guest continued access to ranges of memory which it shouldn't have access to anymore (CVE-2021-28696). Affected products include: Xen, Fedoraproject Fedora, Debian Debian Linux.
Know when Xen gets its next vulnerability
- Watch products and get an email when something new is published
- Check this CVE against your own stack and servers
- Exploit and PoC references, threat intelligence from 22 sources
No credit card · 7-day full trial
Severity by source
AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Primary rating from NVD · only source for this CVE.
CVSS VectorNVD
DescriptionNVD
IOMMU page mapping issues on x86 T[his CNA information record relates to multiple CVEs; the text explains which aspects/vulnerabilities correspond to which CVE.] Both AMD and Intel allow ACPI tables to specify regions of memory which should be left untranslated, which typically means these addresses should pass the translation phase unaltered. While these are typically device specific ACPI properties, they can also be specified to apply to a range of devices, or even all devices. On all systems with such regions Xen failed to prevent guests from undoing/replacing such mappings (CVE-2021-28694). On AMD systems, where a discontinuous range is specified by firmware, the supposedly-excluded middle range will also be identity-mapped (CVE-2021-28695). Further, on AMD systems, upon de-assigment of a physical device from a guest, the identity mappings would be left in place, allowing a guest continued access to ranges of memory which it shouldn't have access to anymore (CVE-2021-28696).
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
Authentication bypass attacks exploit flaws in the verification mechanisms that control access to systems and applications.
Affected Products (CPE)NVD
The x86-64 kernel system-call functionality in Xen 4.1.2 and earlier, as used in Citrix XenServer 6.0.2 and earlier and
The Floppy Disk Controller (FDC) in QEMU, as used in Xen 4.5.x and earlier and KVM, allows local guest users to cause a
A statement in the System Programming Guide of the Intel 64 and IA-32 Architectures Software Developer's Manual (SDM) wa
The AdSanity plugin for WordPress is vulnerable to arbitrary file uploads due to missing file type validation in the 'aj
An issue was discovered in Xen through 4.9.x allowing x86 PV guest OS users to cause a denial of service (unbounded recu
An issue (known as XSA-212) was discovered in Xen, with fixes available for 4.8.x, 4.7.x, 4.6.x, 4.5.x, and 4.4.x. Rated
The C+ mode offload emulation in the RTL8139 network card device model in QEMU, as used in Xen 4.5.x and earlier, allows
Xen, when used on a system providing PV backends, allows local guest OS administrators to cause a denial of service (hos
x86 pv: Insufficient care with non-coherent mappings T[his CNA information record relates to multiple CVEs; the text exp
Xen through 4.8.x does not validate memory allocations during certain P2M operations, which allows guest OS users to obt
Xen through 4.8.x mishandles page transfer, which allows guest OS users to obtain privileged host OS access, aka XSA-217
The grant-table feature in Xen through 4.8.x does not ensure sufficient type counts for a GNTMAP_device_map and GNTMAP_h
GitHub PoC
Exploit-DB