CVE-2020-11739

NameCVE-2020-11739
DescriptionAn issue was discovered in Xen through 4.13.x, allowing guest OS users to cause a denial of service or possibly gain privileges because of missing memory barriers in read-write unlock paths. The read-write unlock paths don't contain a memory barrier. On Arm, this means a processor is allowed to re-order the memory access with the preceding ones. In other words, the unlock may be seen by another processor before all the memory accesses within the "critical" section. As a consequence, it may be possible to have a writer executing a critical section at the same time as readers or another writer. In other words, many of the assumptions (e.g., a variable cannot be modified after a check) in the critical sections are not safe anymore. The read-write locks are used in hypercalls (such as grant-table ones), so a malicious guest could exploit the race. For instance, there is a small window where Xen can leak memory if XENMAPSPACE_grant_table is used concurrently. A malicious guest may be able to leak memory, or cause a hypervisor crash resulting in a Denial of Service (DoS). Information leak and privilege escalation cannot be excluded.
SourceCVE (at NVD; CERT, LWN, oss-sec, fulldisc, bugtraq, EDB, Metasploit, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, Mageia, GitHub code/issues, web search, more)
NVD severitymedium

Vulnerable and fixed packages

The table below lists information on source packages.

Source PackageReleaseVersionStatus
xen (PTS)jessie4.4.1-9+deb8u10vulnerable
jessie (security)4.4.4lts5-0+deb8u1vulnerable
stretch (security), stretch4.8.5.final+shim4.10.4-1+deb9u12vulnerable
buster, buster (security)4.11.3+24-g14b62ab3e5-1~deb10u1vulnerable
bullseye, sid4.11.4-1fixed

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

PackageTypeReleaseFixed VersionUrgencyOriginDebian Bugs
xensource(unstable)4.11.4-1
xensourcejessie(unfixed)end-of-life
xensourcestretch(unfixed)end-of-life

Notes

[buster] - xen <postponed> (Can be fixed along in future Xen DSA)
[stretch] - xen <end-of-life> (DSA 4602-1)
[jessie] - xen <end-of-life> (Not supported in jessie LTS)
https://xenbits.xen.org/xsa/advisory-314.html

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