CVE-2026-99258
x86/hyperv: Avoid using per-cpu output page in hv_apicid_to_vp_index()
What happened?
In the Linux kernel, the following vulnerability has been resolved:
x86/hyperv: Avoid using per-cpu output page in hv_apicid_to_vp_index()
hv_apicid_to_vp_index() currently uses the per-cpu hypercall input and output pages. This function is called when running in VTL2 and when running in an SEV-SNP CoCo VM with no paravisor. In the former case, the output page is allocated, but in the latter case it is not, so the hypervisor stores the output VP index in memory that has not been allocated by the guest.
Fix this by using the input page for both input and output. The hypercall has very small input and output, so sharing the same page for both is straightforward. An alternative fix is to allocate the per-cpu output page when running in an SEV-SNP CoCo guest, but this uses significantly more memory, particularly with larger vCPUs counts.
Affected software and versions
| Software | Version information | Fixed version |
|---|---|---|
| LinuxLinux | affected: 3d12349ade541eefde0e71bf5c4aa7aa04c52a79 to < bdba5f1b8bd0d18b1df61f769b559ed272902489; affected: 86c48271e0d60c82665e9fd61277002391efcef7 to < 2b561786c9076a892ef8b8f416c9828bc87ed44f; affected: 86c48271e0d60c82665e9fd61277002391efcef7 to < bc8ca0f4769627ae7d04e7ffdbd20de4f27a9bf9; affected: 86c48271e0d60c82665e9fd61277002391efcef7 to < 7b74c117e2aac78e0f723e1c9c3644451c56b0d9; affected: cb002d6c8f06d6061e84b2109cb84416107a9fb9; affected: 6.12.41 to < 6.12.115; affected: 6.15.3 to < 6.16 | See vendor advisory |
| LinuxLinux | affected: 6.16; unaffected: 0 to < 6.16; unaffected: 6.12.115 to ≤ 6.12.*; unaffected: 6.18.59 to ≤ 6.18.*; unaffected: 7.2.13 to ≤ 7.2.*; unaffected: 7.3 to ≤ * | See vendor advisory |
Version information comes from the source record and can include unaffected products and exceptions. Distribution packages may contain backported fixes: an older upstream version alone does not prove a server is affected.
Is it being exploited?
This CVE was not listed in the CISA catalogue at our last retrieval. This does not establish that exploitation is absent.
How to respond
- Confirm the product, installed package version, and any configuration requirements in the vendor advisory.
- Follow the vendor’s remediation or workaround guidance in the references below. Structured fixed-version data is unavailable here; the publisher’s description may include a fix or workaround.
- Restart affected services if required, then verify the running version. Known exploitation may warrant investigation as well as patching.
Sources and remediation references
- https://www.cve.org/CVERecord?id=CVE-2026-99258
- https://git.kernel.org/stable/c/bdba5f1b8bd0d18b1df61f769b559ed272902489
- https://git.kernel.org/stable/c/2b561786c9076a892ef8b8f416c9828bc87ed44f
- https://git.kernel.org/stable/c/bc8ca0f4769627ae7d04e7ffdbd20de4f27a9bf9
- https://git.kernel.org/stable/c/7b74c117e2aac78e0f723e1c9c3644451c56b0d9