CVE-2020-25603

NameCVE-2020-25603
DescriptionAn issue was discovered in Xen through 4.14.x. There are missing memory barriers when accessing/allocating an event channel. Event channels control structures can be accessed lockless as long as the port is considered to be valid. Such a sequence is missing an appropriate memory barrier (e.g., smp_*mb()) to prevent both the compiler and CPU from re-ordering access. A malicious guest may be able to cause a hypervisor crash resulting in a Denial of Service (DoS). Information leak and privilege escalation cannot be excluded. Systems running all versions of Xen are affected. Whether a system is vulnerable will depend on the CPU and compiler used to build Xen. For all systems, the presence and the scope of the vulnerability depend on the precise re-ordering performed by the compiler used to build Xen. We have not been able to survey compilers; consequently we cannot say which compiler(s) might produce vulnerable code (with which code generation options). GCC documentation clearly suggests that re-ordering is possible. Arm systems will also be vulnerable if the CPU is able to re-order memory access. Please consult your CPU vendor. x86 systems are only vulnerable if a compiler performs re-ordering.
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)
ReferencesDSA-4769-1
NVD severitymedium

Vulnerable and fixed packages

The table below lists information on source packages.

Source PackageReleaseVersionStatus
xen (PTS)stretch (security), stretch4.8.5.final+shim4.10.4-1+deb9u12vulnerable
buster4.11.4+24-gddaaccbbab-1~deb10u1vulnerable
buster (security)4.11.4+37-g3263f257ca-1fixed
bullseye, sid4.11.4+24-gddaaccbbab-1vulnerable

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

PackageTypeReleaseFixed VersionUrgencyOriginDebian Bugs
xensourcestretch(unfixed)end-of-life
xensourcebuster4.11.4+37-g3263f257ca-1DSA-4769-1
xensource(unstable)(unfixed)

Notes

[stretch] - xen <end-of-life> (DSA 4602-1)
https://xenbits.xen.org/xsa/advisory-340.html

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