High [CVE-2026-53360] Require in-GHCB scratch area if GHCB v2+ is in use
This high-severity Red Hat Linux advisory covers CVE-2026-53360 affecting Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat package: kernel-rt.
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Summary
In the Linux kernel, the following vulnerability has been resolved: KVM: SEV: Require in-GHCB scratch area if GHCB v2+ is in use As per the GHCB spec, when using GHCB v2+ require the software scratch area to reside in the GHCB's shared buffer.
Note, things like Page State Change (PSC) requests _rely_ on this behavior, as the guest can't provide a length when making the request, i.e. the size of the guest payload is bounded by the size of the shared buffer.
Failure to force usage of the GHCB, and a slew of other flaws, lets a malicious SNP guest corrupt host kernel heap memory, and leak host heap layout information. setup_vmgexit_scratch() allocates a buffer via kvzalloc(exit_info_2), where exit_info_2 is guest-controlled.
With exit_info_2=24, this yields a 24-byte allocation in kmalloc-cg-32 (32-byte slab objects).
The buffer holds an 8-byte psc_hdr followed by 8-byte psc_entry structs, so only entries[0] and entries[1] are in-bounds. snp_begin_psc() validates end_entry against VMGEXIT_PSC_MAX_COUNT (253) but NOT against the actual buffer size: idx_end = hdr->end_entry; if (idx_end >= VMGEXIT_PSC_MAX_COUNT) { // checks 253, not buffer snp_complete_psc(svm,...); return 1; } for (idx = idx_start; idx = 2 The guest sets end_entry=10+, causing the host to iterate entries[2+] which are OOB into adjacent slab objects.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · high-confidence parse· fetched 21 days ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · high-confidence parse· fetched 21 days ago·verify at source
Mitigation checklist
- If confidential VMs are not in use, this vulnerability can be mitigated by disabling SEV-SNP support on the host, removing the attack surface entirely. Create a file in `/etc/modprobe.d/` with a descriptive name, such as `cve-2026-53360-mitigation.conf`. In that file, disable SEV-SNP for the `kvm_amd` kernel module: ``` options kvm_amd sev_snp=0 ``` To validate, read the file `/sys/module/kvm_amd/parameters/sev_snp`. This file should read `N` to indicate that the feature is disabled. If SEV-SNP cannot be disabled, run SEV-SNP hosts on isolated environments and restrict the ability to create SNP-enabled VMs to trusted tenants/administrators only.
Official advisory · high-confidence parse· fetched 21 days ago·verify at source
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