Vulnerability Details : CVE-2021-28689
x86: Speculative vulnerabilities with bare (non-shim) 32-bit PV guests 32-bit x86 PV guest kernels run in ring 1. At the time when Xen was developed, this area of the i386 architecture was rarely used, which is why Xen was able to use it to implement paravirtualisation, Xen's novel approach to virtualization. In AMD64, Xen had to use a different implementation approach, so Xen does not use ring 1 to support 64-bit guests. With the focus now being on 64-bit systems, and the availability of explicit hardware support for virtualization, fixing speculation issues in ring 1 is not a priority for processor companies. Indirect Branch Restricted Speculation (IBRS) is an architectural x86 extension put together to combat speculative execution sidechannel attacks, including Spectre v2. It was retrofitted in microcode to existing CPUs. For more details on Spectre v2, see: http://xenbits.xen.org/xsa/advisory-254.html However, IBRS does not architecturally protect ring 0 from predictions learnt in ring 1. For more details, see: https://software.intel.com/security-software-guidance/deep-dives/deep-dive-indirect-branch-restricted-speculation Similar situations may exist with other mitigations for other kinds of speculative execution attacks. The situation is quite likely to be similar for speculative execution attacks which have yet to be discovered, disclosed, or mitigated.
Vulnerability category: Overflow
Exploit prediction scoring system (EPSS) score for CVE-2021-28689
Probability of exploitation activity in the next 30 days: 0.04%
Percentile, the proportion of vulnerabilities that are scored at or less: ~ 10 % EPSS Score History EPSS FAQ
CVSS scores for CVE-2021-28689
Base Score | Base Severity | CVSS Vector | Exploitability Score | Impact Score | Score Source |
---|---|---|---|---|---|
2.1
|
LOW | AV:L/AC:L/Au:N/C:P/I:N/A:N |
3.9
|
2.9
|
NIST |
5.5
|
MEDIUM | CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N |
1.8
|
3.6
|
NIST |
CWE ids for CVE-2021-28689
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The product performs operations on a memory buffer, but it can read from or write to a memory location that is outside of the intended boundary of the buffer.Assigned by: nvd@nist.gov (Primary)
References for CVE-2021-28689
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https://xenbits.xenproject.org/xsa/advisory-370.txt
Vendor Advisory
Products affected by CVE-2021-28689
- cpe:2.3:o:xen:xen:*:*:*:*:*:*:*:*