#VU31973 Buffer overflow in Xen - CVE-2020-11739
Vulnerability identifier: #VU31973
Vulnerability risk: Medium
CVSSv4.0: 5.6 [CVSS:4.0/AV:A/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H/E:U/U:Green]
CVE-ID:
CWE-ID:
CWE-119
Exploitation vector: Local network
Exploit availability: No
Vulnerable software:
Xen
Server applications /
Virtualization software
Vendor: Xen Project
Description
The vulnerability allows a remote user to perform a denial of service (DoS) attack.
An 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).Mitigation
Install updates from vendor's website.
Vulnerable software versions
Xen: 4.0.0 - 4.13.0
External links
https://lists.opensuse.org/opensuse-security-announce/2020-05/msg00006.html
https://www.openwall.com/lists/oss-security/2020/04/14/2
https://xenbits.xen.org/xsa/advisory-314.html
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/5M2XRNCHOGGTJQBZQJ7DCV6ZNAKN3LE2/
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/NVTP4OYHCTRU3ONFJOFJQVNDFB25KLLG/
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/YMAW7D2MP6RE4BFI5BZWOBBWGY3VSOFN/
https://security.gentoo.org/glsa/202005-08
https://www.debian.org/security/2020/dsa-4723
https://xenbits.xen.org/xsa/advisory-314.html
Q & A
Can this vulnerability be exploited remotely?
Yes. This vulnerability can be exploited by a remote authenticated user via the local network (LAN).
Is there known malware, which exploits this vulnerability?
No. We are not aware of malware exploiting this vulnerability.
