CVE-2021-28689 Information disclosure in Xen

What is CVE-2021-28689?

CVE-2021-28689 is a medium-severity vulnerability in Xen Xen, published on 11 Jun 2021. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

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.

Weakness: CWE-212

Which versions are affected by CVE-2021-28689?

It affects 1 product.

Products include Xen Xen.

How do I fix CVE-2021-28689?

Apply the vendor's patch.

Is CVE-2021-28689 being exploited?

There is no known exploitation of CVE-2021-28689 in the wild and no public exploit code.

Other vulnerabilities in Xen Xen

• CVE-2017-10912 Privilege escalation in n/a Critical 10.0
• CVE-2017-10918 Memory corruption in n/a Critical 10.0
• CVE-2017-10920 Memory corruption in n/a Critical 10.0
• CVE-2017-10921 Memory corruption in n/a Critical 10.0
• CVE-2025-27466 Mutiple vulnerabilities in the Viridian interface Critical 9.8

All Xen Xen vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as DEBIAN-CVE-2021-28689, GHSA-45vh-fhgx-cr2p, SUSE-SU-2021:1648-1, UBUNTU-CVE-2021-28689.