CVE-2021-28703

NameCVE-2021-28703
Descriptiongrant table v2 status pages may remain accessible after de-allocation (take two) Guest get 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, get de-allocated when a guest switched (back) from v2 to v1. The freeing of such pages requires that the hypervisor know where in the guest these pages were mapped. The hypervisor tracks only one use within guest space, but racing requests from the guest to insert mappings of these pages may result in any of them to become mapped in multiple locations. Upon switching back from v2 to v1, the guest would then retain access to a page that was freed and perhaps re-used for other purposes. This bug was fortuitously fixed by code cleanup in Xen 4.14, and backported to security-supported Xen branches as a prerequisite of the fix for XSA-378.
SourceCVE (at NVD; CERT, LWN, oss-sec, fulldisc, bugtraq, EDB, Metasploit, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, Mageia, GitHub advisories/code/issues, web search, more)

Vulnerable and fixed packages

The table below lists information on source packages.

Source PackageReleaseVersionStatus
xen (PTS)buster, buster (security)4.11.4+107-gef32c7afa2-1vulnerable
bullseye4.14.5+24-g87d90d511c-1fixed
bullseye (security)4.14.5+86-g1c354767d5-1fixed
bookworm, sid4.16.2+90-g0d39a6d1ae-1fixed

The information below is based on the following data on fixed versions.

PackageTypeReleaseFixed VersionUrgencyOriginDebian Bugs
xensourcestretch(unfixed)end-of-life
xensourcebuster(unfixed)end-of-life
xensource(unstable)4.14.0+80-gd101b417b7-1

Notes

[buster] - xen <end-of-life> (DSA 4677-1)
[stretch] - xen <end-of-life> (DSA 4602-1)
https://xenbits.xen.org/xsa/advisory-387.html
Fixed by code cleanup in Xen 4.14, and backported to security-supported Xen branches
as a prerequisite of the fix for XSA-378. 4.14.0-1~exp1 was the first version in
Debian including the fix.
https://xenbits.xen.org/gitweb/?p=xen.git;a=commit;h=c65ea16dbcafbe4fe21693b18f8c2a3c5d14600e (4.14.0-rc1)

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