Vulnerability in Xen
CVE-2021-28701
Another race in XENMAPSPACE_grant_table handling Guests are permitted access to certain Xen-owned pages of memory. The majority of such pages remain allocated / associated with a guest for its entire lifetime. Grant table v2 status pages, however, are de-allocated when a guest switches (back) from v2 to v1. Freeing such pages requires that the hypervisor enforce that no parallel request can result in the addition of a mapping of such a page to a guest. That enforcement was missing, allowing guests to retain access to pages that were freed and perhaps re-used for other purposes. Unfortunately, when XSA-379 was being prepared, this similar issue was not noticed.
Vulnerability class: Race Condition
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.8 (High). Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H.
EPSS exploit prediction
EPSS: 0.003 (16.7th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 17th percentile — 16.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.003 · change: 0.000
Affected products
- Xen — versions unspecified, 4.15.x, next of xen-unstable
- 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-384.txt (Vendor Advisory)
- xenbits.xen.org/xsa/advisory-384.html (Vendor Advisory)
- www.openwall.com/lists/oss-security/2021/09/08/2 (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-2021-28701?
- CVE-2021-28701 is a high-severity vulnerability in Xen, classified under Concurrent Execution using Shared Resource with Improper Synchronization (Race Condition). CVSS score: 7.8/10. Published 2021-09-08.
- How severe is CVE-2021-28701?
- High severity. CVSS v3 base score is 7.8 out of 10.
- Is CVE-2021-28701 known to be exploited?
- 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.