CVE-2021-28697

Name	CVE-2021-28697
Description	grant table v2 status pages may remain accessible after de-allocation 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.
Source	CVE (at NVD; CERT, LWN, oss-sec, fulldisc, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)
References	DSA-4977-1

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
xen (PTS)	jessie, jessie (lts)	4.4.4lts5-0+deb8u1	vulnerable
	stretch (security), stretch (lts), stretch	4.8.5.final+shim4.10.4-1+deb9u12	vulnerable
	buster (security), buster, buster (lts)	4.11.4+107-gef32c7afa2-1	vulnerable
	bullseye	4.14.6-1	fixed
	bullseye (security)	4.14.5+94-ge49571868d-1	fixed
	bookworm	4.17.3+10-g091466ba55-1~deb12u1	fixed
	sid, trixie	4.17.3+36-g54dacb5c02-1	fixed

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

Package	Type	Release	Fixed Version	Urgency	Origin
xen	source	jessie	(unfixed)	end-of-life
xen	source	stretch	(unfixed)	end-of-life
xen	source	buster	(unfixed)	end-of-life
xen	source	bullseye	4.14.3-1~deb11u1		DSA-4977-1
xen	source	(unstable)	4.14.3-1

[buster] - xen <end-of-life> (DSA 4677-1)
[stretch] - xen <end-of-life> (DSA 4602-1)
https://xenbits.xen.org/xsa/advisory-379.html