PwnEscape (CVE-2026-99999)
Hypervisors running untrusted virtio-net VMs on an affected kernel are potentially exposed. Update the host kernel and reboot the hypervisor during a planned maintenance window.
Summary
| Field | Detail |
|---|---|
| CVE | CVE-2026-99999 |
| Name | PwnEscape |
| Component | Linux host networking, IPv4 checksum completion; reachable through virtio-net/TAP |
| Impact | Host memory disclosure and denial of service; the researcher also reports host code execution in a controlled lab |
| Severity | Kernel CNA: CVSS 3.1 9.3 Critical; Red Hat assigns 8.8 and a Critical severity rating |
| Upstream fix | 6785011f8b16abf40b1e9d8b2e332232b3e68822 |
| Status checked | 18 October 2026 |
The researcher demonstrated host memory disclosure and subsequently achieved VM-to-host code execution in a controlled lab. AWS's bulletin independently identifies the affected self-managed KVM/virtio-net configuration. Red Hat's assessment includes possible host code execution, crashes and information disclosure.
Am I affected?
Assess the running host kernel on every hypervisor that accepts untrusted VM workloads using virtio-net with TAP or vhost-net networking. Patch status depends on the host kernel and its vendor security updates.
Assess Intel, AMD and arm64 hosts. Reachability depends on their networking configuration and kernel patches, including hosts with nested virtualization disabled.
The VM-to-host attack path applies to hypervisors hosting tenant VMs. Maintain operating-system security updates on control servers as usual.
What the fix changes
A VM can supply checksum-offload metadata alongside a packet. The host may parse the packet before completing its checksum. Invalid checksum positioning can cause that later operation to change an IPv4 header that the stack already examined, making later consumers operate on inconsistent packet data.
The upstream patch checks that checksum processing starts beyond the IPv4 header before allowing completion in several networking paths, including fragmentation and bridge connection tracking. The commit explicitly describes this as defensive validation and notes broader input validation work. Install vendor security updates as they become available, including subsequent hardening.
Is a fix available for my distribution?
Checked on 18 October 2026 at 06:07 UTC. Availability below refers to a vendor-published security fix in the distribution's stable repositories.
| Distribution | Fix available? | Details |
|---|---|---|
| Debian 12 (bookworm) | Yes | Install linux 6.1.190-1 or a later security update. Fixed by DLA-4841-1. |
| Debian 13 (trixie) | Yes | Install linux 6.12.113-1 or a later security update. Fixed by DSA-6568-1. |
| Ubuntu 22.04 LTS | No | No fixed build listed. Ubuntu marks the generic and maintained HWE kernels as awaiting evaluation. |
| Ubuntu 24.04 LTS | No | No fixed build listed. Ubuntu marks the generic and maintained HWE kernels as awaiting evaluation. |
| AlmaLinux 9 | No | No fix for this CVE listed in stable BaseOS security update metadata. |
| AlmaLinux 10 | No | No fix for this CVE listed in stable BaseOS security update metadata. |
| Rocky Linux 9 | No | No fix for this CVE listed in stable BaseOS security update metadata. |
| Rocky Linux 10 | No | No fix for this CVE listed in stable BaseOS security update metadata. |
Debian 12 and 13's fixed packages were verified in the security repository for amd64 and arm64. AlmaLinux and Rocky Linux's BaseOS security metadata was checked for x86_64 and aarch64. Debian 12 backports and custom kernels require a separate check against their package security records.
Sources: Debian 12 security repository, Debian CVE tracker, Debian 13 security repository, Ubuntu CVE tracker, AlmaLinux 9 repository metadata, AlmaLinux 10 repository metadata, Rocky Linux 9 repository metadata, Rocky Linux 10 repository metadata.
Remediation
Debian 12 and 13: update and reboot
Run on the hypervisor:
apt-get update
apt-get install "linux-image-$(dpkg --print-architecture)"
reboot
After reboot, verify the running kernel and package:
uname -r
dpkg-query -W "linux-image-$(uname -r)"
The fixed packages are:
- Debian 12:
6.1.190-1, with kernel release6.1.0-54-amd64or6.1.0-54-arm64. - Debian 13:
6.12.113-1, with kernel release6.12.113+deb13-amd64or6.12.113+deb13-arm64.
Later vendor security kernels also include the fix.
Distributions awaiting a fix
Monitor the vendor record linked in the table and install the fixed kernel as soon as it is released. Reboot the hypervisor to apply it.
While a vendor fix is unavailable
AWS and Red Hat identify no generally suitable workaround. Follow the vendor's security updates for the distributions marked No above.
For live patching, confirm with the provider that its patch covers this CVE on the exact running kernel.