CVE-2026-99178: Linux kernel · x86/kvm: Don't consume async #PF flags on a kernel #PF in NMI context
Affects Linux kernelSource GCVE Database
Not known to be exploited.
Data as of 30 Oct 2026, 03:51 UTC
Rated by Threat Radar · CVSS not yet scored by NVD
Thin evidence
One scorer or noneExploitation evidence
Disclosed: evidence found.
CVE published 28 Oct 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 29 Oct 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 for this vulnerability is available and should be applied to affected Linux kernel versions. The patch prevents the kernel panic by preserving async #PF flags during kernel page faults in NMI context. Systems running affected kernel versions with KVM nested virtualization should upgrade to a patched kernel release to avoid host crashes. No additional mitigations are indicated beyond applying the official fix.
Description
CVE-2026-99178 is a Linux kernel vulnerability affecting the x86 KVM subsystem. It involves improper handling of asynchronous page fault (#PF) flags during nested machine check or debug exceptions (NMI context). This flaw can cause a kernel panic when an NMI handler takes a page fault and clears flags belonging to the interrupted handler, leading to a crash. The issue was observed in scenarios involving KVM running as an L1 hypervisor and perf sampling with user call chains. The patch prevents consuming async #PF flags in kernel #PF in NMI context, avoiding the panic.
References
- ubuntu.com/security/CVE-2026-99178 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2026-99178 (opens in a new tab)
- git.kernel.org/stable/c/f45ee1ff6358a22d7e22a4c53cb3148ea97b10d9 (opens in a new tab)
- git.kernel.org/stable/c/b77e9622bbade9812e2090c66d25c372f515e921 (opens in a new tab)
- git.kernel.org/stable/c/81d99abe2bd81379abfb595e403bbbee6fbfc624 (opens in a new tab)