CVE-2026-99258: Linux kernel · x86/hyperv: Avoid using per-cpu output page in hv_apicid_to_vp_index()
Affects Linux kernelSource GCVE Database
Not known to be exploited.
Data as of 5 Nov 2026, 00:01 UTC
Rated by Threat Radar · CVSS not yet scored by NVD
Thin evidence
One scorer or none- EPSS
- 0.1% chance of exploitation in 30 days – higher than 8% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Exploitation evidence
Disclosed: evidence found.
CVE published 3 Nov 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 4 Nov 2026.
What to do
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Ubuntu 26.10linuxpkg:deb/ubuntu/linux?arch=source&distro=stonkingOther threats | Affected
| Fixed in– |
Ubuntu 26.10linux-awspkg:deb/ubuntu/linux-aws?arch=source&distro=stonkingOther threats | Affected
| Fixed in– |
Ubuntu 26.10linux-azurepkg:deb/ubuntu/linux-azure?arch=source&distro=stonkingOther threats | Affected
| Fixed in– |
Ubuntu 26.10linux-azure-fdepkg:deb/ubuntu/linux-azure-fde?arch=source&distro=stonkingOther threats | Affected
| Fixed in– |
Ubuntu 26.10linux-gcppkg:deb/ubuntu/linux-gcp?arch=source&distro=stonkingOther threats | Affected
| Fixed in– |
Ubuntu 26.10linux-oraclepkg:deb/ubuntu/linux-oracle?arch=source&distro=stonkingOther threats | Affected
| Fixed in– |
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
A fix is available that changes the hv_apicid_to_vp_index() function to use the input page for both input and output, preventing writes to unallocated memory. Users should apply the updated Linux kernel versions that include this fix. No alternative mitigation is required as the patch addresses the root cause directly.
Description
A vulnerability in the Linux kernel's x86 Hyper-V code involves improper use of per-CPU output pages in the hv_apicid_to_vp_index() function. This function uses per-CPU hypercall input and output pages, but in certain virtual machine configurations, the output page is not allocated, leading to the hypervisor writing output to unallocated memory. The issue is fixed by using the input page for both input and output, avoiding unallocated memory usage.
References
- ubuntu.com/security/CVE-2026-99258 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2026-99258 (opens in a new tab)
- git.kernel.org/stable/c/7b74c117e2aac78e0f723e1c9c3644451c56b0d9 (opens in a new tab)
- git.kernel.org/stable/c/bdba5f1b8bd0d18b1df61f769b559ed272902489 (opens in a new tab)
- git.kernel.org/stable/c/bc8ca0f4769627ae7d04e7ffdbd20de4f27a9bf9 (opens in a new tab)
- git.kernel.org/stable/c/2b561786c9076a892ef8b8f416c9828bc87ed44f (opens in a new tab)