Auth bypass in Xen
CVE-2021-28696
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).
Vulnerability class: Broken Access Control
Published · last modified .
CVSS v3 metric
CVSS v3 base score 6.8 (Medium). Vector: CVSS:3.1/AV:P/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.004 (27.9th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 28th percentile — 27.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: 0.000
Affected products
- Xen — versions 4.11.x, xen-unstable, 4.12.x
- Debian Linux — versions 11.0
- Fedoraproject Fedora — versions 33, 34, 35
Weakness classification (CWE)
Public proof-of-concept exploits
References
- xenbits.xenproject.org/xsa/advisory-378.txt (Vendor Advisory)
- www.openwall.com/lists/oss-security/2021/09/01/1 (mailing-list, Mailing List, Third Party Advisory)
- www.openwall.com/lists/oss-security/2021/09/01/5 (mailing-list, Mailing List, Third Party Advisory)
- www.openwall.com/lists/oss-security/2021/09/01/6 (mailing-list, Mailing List, Third Party Advisory)
- lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/… (vendor-advisory)
- lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/… (vendor-advisory)
- www.debian.org/security/2021/dsa-4977 (vendor-advisory, Third Party Advisory)
- lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/… (vendor-advisory)
- security.gentoo.org/glsa/202208-23 (vendor-advisory, Third Party Advisory)
Frequently asked questions
- What is CVE-2021-28696?
- CVE-2021-28696 is a medium-severity vulnerability in Xen, classified under Incorrect Authorization. CVSS score: 6.8/10. Published 2021-08-27.
- How severe is CVE-2021-28696?
- Medium severity. CVSS v3 base score is 6.8 out of 10.
- Is CVE-2021-28696 known to be exploited?
- 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.