{"id":"CVE-2020-25603","details":"An 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.","modified":"2026-03-13T00:36:56.665852Z","published":"2020-09-23T22:15:13.853Z","related":["SUSE-SU-2020:14521-1","SUSE-SU-2020:2786-1","SUSE-SU-2020:2787-1","SUSE-SU-2020:2788-1","SUSE-SU-2020:2789-1","SUSE-SU-2020:2790-1","SUSE-SU-2020:2791-1","SUSE-SU-2020:2822-1","openSUSE-SU-2020:1608-1","openSUSE-SU-2024:11520-1"],"references":[{"type":"WEB","url":"https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/4JRXMKEMQRQYWYEPHVBIWUEAVQ3LU4FN/"},{"type":"WEB","url":"https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/DA633Y3G5KX7MKRN4PFEGM3IVTJMBEOM/"},{"type":"WEB","url":"https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RJZERRBJN6E6STDCHT4JHP4MI6TKBCJE/"},{"type":"ADVISORY","url":"https://www.debian.org/security/2020/dsa-4769"},{"type":"ADVISORY","url":"http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00008.html"},{"type":"ADVISORY","url":"https://security.gentoo.org/glsa/202011-06"},{"type":"FIX","url":"https://xenbits.xen.org/xsa/advisory-340.html"}],"affected":[{"database_specific":{"unresolved_ranges":[{"events":[{"introduced":"0"},{"last_affected":"4.14.0"}]},{"events":[{"introduced":"0"},{"last_affected":"31"}]},{"events":[{"introduced":"0"},{"last_affected":"32"}]},{"events":[{"introduced":"0"},{"last_affected":"33"}]},{"events":[{"introduced":"0"},{"last_affected":"15.2"}]},{"events":[{"introduced":"0"},{"last_affected":"10.0"}]}],"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2020-25603.json"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"}]}