In early August 2026, five security advisories were published affecting the Proxmox platform and the Linux kernel:
- Zapscape (CVE-2026-64561, PSA-2026-00036-1), a use-after-free in the shadow MMU emulation code of KVM on x86_64. Under the right nested virtualization conditions, a privileged attacker inside a guest can corrupt host kernel memory, cross the guest/host isolation boundary and execute code as root on the host. It is the successor to Januscape (CVE-2026-53359), disclosed a month earlier in the same code.
- SCTPhantom (CVE-2026-64564, PSA-2026-00037-1), a use-after-free in the kernel's SCTP Dynamic Address Reconfiguration (ASCONF) handling. A crafted ASCONF sequence leaves the association holding a stale transport pointer, which a local unprivileged user can turn into full root and, in some configurations, a container escape. The flawed logic dates back to kernel 2.6.25 (2007), making this an 18 year old bug. CVSS 4.0 score 8.5.
- TONTOU (PSA-2026-00038-1), a speculative execution attack against Spectre v2 defences. An unprivileged process injects precisely timed timer interrupts to re-poison the branch predictor in the short window after the mitigation has neutralised it but before the protected branch executes, leaking arbitrary kernel memory including password hashes.
- PSA-2026-00034-1, missing validation of the
commentfield in the Proxmox firewall API, which allowed an authenticated user with write access to any firewall scope to inject arbitrary lines into the firewall configuration files. - PSA-2026-00035-1, missing
VM.PowerMgmtprivilege checks when a container is started directly after creation or after a snapshot rollback.
All five issues were handled with the highest priority. The full virtualisation and hosting infrastructure was updated as soon as fixed kernels and packages were released, and every node now runs fully patched kernels, firewall and container packages. There are no indications of exploitation on our platform and customer data was not at risk at any point.
The two Proxmox advisories (PSA-2026-00034-1 and PSA-2026-00035-1) and the Zapscape KVM escape affect the hypervisor layer only. These are entirely our responsibility and require no action from you.
SCTPhantom and TONTOU also affect guest systems independently of the host, so we recommend that you update the operating system inside your VPS and dedicated servers as well. On most distributions a standard package update and a reboot is sufficient. If SCTP is not in use, unloading or blacklisting the sctp module mitigates SCTPhantom until you can reboot.
If you run containers inside your VPS or dedicated server (Docker, LXC, Kubernetes), treat the update as a priority, since SCTPhantom allows an escape from the container to root on the guest system.
Security patching of this kind is part of our ongoing commitment to the safety of your services. If you have any questions, we are available through the support system.
