{"id":"CVE-2026-53360","state":"PUBLISHED","title":"KVM: SEV: Require in-GHCB scratch area if GHCB v2+ is in use","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: SEV: Require in-GHCB scratch area if GHCB v2+ is in use\n\nAs per the GHCB spec, when using GHCB v2+ require the software scratch area\nto reside in the GHCB's shared buffer.  Note, things like Page State Change\n(PSC) requests _rely_ on this behavior, as the guest can't provide a length\nwhen making the request, i.e. the size of the guest payload is bounded by\nthe size of the shared buffer.\n\nFailure to force usage of the GHCB, and a slew of other flaws, lets a\nmalicious SNP guest corrupt host kernel heap memory, and leak host heap\nlayout information.\n\nsetup_vmgexit_scratch() allocates a buffer via kvzalloc(exit_info_2),\nwhere exit_info_2 is guest-controlled. With exit_info_2=24, this yields\na 24-byte allocation in kmalloc-cg-32 (32-byte slab objects). The buffer\nholds an 8-byte psc_hdr followed by 8-byte psc_entry structs, so only\nentries[0] and entries[1] are in-bounds.\n\nsnp_begin_psc() validates end_entry against VMGEXIT_PSC_MAX_COUNT (253)\nbut NOT against the actual buffer size:\n\n      idx_end = hdr->end_entry;\n\n      if (idx_end >= VMGEXIT_PSC_MAX_COUNT) {   // checks 253, not buffer\n          snp_complete_psc(svm, ...);\n          return 1;\n      }\n\n      for (idx = idx_start; idx <= idx_end; idx++) {\n          entry_start = entries[idx];           // OOB when idx >= 2\n\nThe guest sets end_entry=10+, causing the host to iterate entries[2+]\nwhich are OOB into adjacent slab objects. For each OOB entry:\n\n  - The host reads 8 bytes (OOB READ / info leak oracle)\n  - If the data passes PSC validation, __snp_complete_one_psc() writes\n    cur_page = 1 or 512 into the entry (OOB WRITE, sev.c:3806)\n  - If validation fails, the error response reveals whether adjacent\n    memory is zero vs non-zero (information disclosure to guest)\n\nThe guest controls allocation size (exit_info_2), entry range\n(cur_entry/end_entry), and can fire unlimited VMGEXITs to repeatedly\nhit different slab positions.\n\nBy exploiting the variety of bugs, a malicious SEV-SNP guest can:\n    - OOB read adjacent kmalloc-cg-32 objects (heap layout disclosure)\n    - OOB write cur_page bits into adjacent objects (heap corruption)\n    - Trigger use-after-free conditions across VMGEXITs\n\nE.g. with KASAN enabled, a single insmod of the PoC guest module\nproduces 73 KASAN reports:\n\n    BUG: KASAN: slab-out-of-bounds in snp_begin_psc+0x126/0x890\n    Read of size 8 at addr ffff888219ffb5e0 by task qemu-system-x86/2199\n\n    BUG: KASAN: slab-out-of-bounds in snp_begin_psc+0x468/0x890\n    Write of size 8 at addr ffff888351566648 by task qemu-system-x86/2199\n\n    The buggy address belongs to the object at ffff888XXXXXXXXX\n     which belongs to the cache kmalloc-cg-32 of size 32\n    The buggy address is located N bytes to the right of\n     allocated 32-byte region [ffff888XXXXXXXXX, ffff888XXXXXXXXX)\n\n  Breakdown:\n    62 slab-out-of-bounds (reads + writes past allocation)\n     7 slab-use-after-free\n     4 use-after-free\n\nAll credit to Stan for the wonderful description and reproducer!\n\n[sean: write changelog]","publishedAt":"2026-07-04T11:53:58.657Z","updatedAt":"2026-10-19T20:07:44.426Z","severity":{"score":8.8,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"4af663c2f64a8d252e690c60cf8b8abf22dc2951","status":"affected","lessThan":"bf9ba093fbb83c0c9a3dedd50efec29424eca2fc","versionType":"git"},{"version":"4af663c2f64a8d252e690c60cf8b8abf22dc2951","status":"affected","lessThan":"c9b4198fbc6ed99a9da4bee9f74bb730f926c9ae","versionType":"git"},{"version":"4af663c2f64a8d252e690c60cf8b8abf22dc2951","status":"affected","lessThan":"b328ede59ac34e7998e1eee5e5f0cc26c2a91846","versionType":"git"},{"version":"4af663c2f64a8d252e690c60cf8b8abf22dc2951","status":"affected","lessThan":"db3f2195d29344a3cf1e9dd9ab7f21ced7308cf7","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["arch/x86/kvm/svm/sev.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.10","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.10","versionType":"semver"},{"version":"6.12.93","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.35","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.0.12","status":"unaffected","lessThanOrEqual":"7.0.*","versionType":"semver"},{"version":"7.1","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["arch/x86/kvm/svm/sev.c"]}],"references":["https://git.kernel.org/stable/c/bf9ba093fbb83c0c9a3dedd50efec29424eca2fc","https://git.kernel.org/stable/c/c9b4198fbc6ed99a9da4bee9f74bb730f926c9ae","https://git.kernel.org/stable/c/b328ede59ac34e7998e1eee5e5f0cc26c2a91846","https://git.kernel.org/stable/c/db3f2195d29344a3cf1e9dd9ab7f21ced7308cf7"],"weaknesses":["CWE-787"],"ingestedAt":"2026-10-29T20:12:16.098Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/53xxx/CVE-2026-53360.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-53360","state":"PUBLISHED","datePublished":"2026-07-04T11:53:58.657Z","dateUpdated":"2026-10-19T20:07:44.426Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-06-09T07:44:35.400Z"},"containers":{"cna":{"title":"KVM: SEV: Require in-GHCB scratch area if GHCB v2+ is in use","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: SEV: Require in-GHCB scratch area if GHCB v2+ is in use\n\nAs per the GHCB spec, when using GHCB v2+ require the software scratch area\nto reside in the GHCB's shared buffer.  Note, things like Page State Change\n(PSC) requests _rely_ on this behavior, as the guest can't provide a length\nwhen making the request, i.e. the size of the guest payload is bounded by\nthe size of the shared buffer.\n\nFailure to force usage of the GHCB, and a slew of other flaws, lets a\nmalicious SNP guest corrupt host kernel heap memory, and leak host heap\nlayout information.\n\nsetup_vmgexit_scratch() allocates a buffer via kvzalloc(exit_info_2),\nwhere exit_info_2 is guest-controlled. With exit_info_2=24, this yields\na 24-byte allocation in kmalloc-cg-32 (32-byte slab objects). The buffer\nholds an 8-byte psc_hdr followed by 8-byte psc_entry structs, so only\nentries[0] and entries[1] are in-bounds.\n\nsnp_begin_psc() validates end_entry against VMGEXIT_PSC_MAX_COUNT (253)\nbut NOT against the actual buffer size:\n\n      idx_end = hdr->end_entry;\n\n      if (idx_end >= VMGEXIT_PSC_MAX_COUNT) {   // checks 253, not buffer\n          snp_complete_psc(svm, ...);\n          return 1;\n      }\n\n      for (idx = idx_start; idx <= idx_end; idx++) {\n          entry_start = entries[idx];           // OOB when idx >= 2\n\nThe guest sets end_entry=10+, causing the host to iterate entries[2+]\nwhich are OOB into adjacent slab objects. For each OOB entry:\n\n  - The host reads 8 bytes (OOB READ / info leak oracle)\n  - If the data passes PSC validation, __snp_complete_one_psc() writes\n    cur_page = 1 or 512 into the entry (OOB WRITE, sev.c:3806)\n  - If validation fails, the error response reveals whether adjacent\n    memory is zero vs non-zero (information disclosure to guest)\n\nThe guest controls allocation size (exit_info_2), entry range\n(cur_entry/end_entry), and can fire unlimited VMGEXITs to repeatedly\nhit different slab positions.\n\nBy exploiting the variety of bugs, a malicious SEV-SNP guest can:\n    - OOB read adjacent kmalloc-cg-32 objects (heap layout disclosure)\n    - OOB write cur_page bits into adjacent objects (heap corruption)\n    - Trigger use-after-free conditions across VMGEXITs\n\nE.g. with KASAN enabled, a single insmod of the PoC guest module\nproduces 73 KASAN reports:\n\n    BUG: KASAN: slab-out-of-bounds in snp_begin_psc+0x126/0x890\n    Read of size 8 at addr ffff888219ffb5e0 by task qemu-system-x86/2199\n\n    BUG: KASAN: slab-out-of-bounds in snp_begin_psc+0x468/0x890\n    Write of size 8 at addr ffff888351566648 by task qemu-system-x86/2199\n\n    The buggy address belongs to the object at ffff888XXXXXXXXX\n     which belongs to the cache kmalloc-cg-32 of size 32\n    The buggy address is located N bytes to the right of\n     allocated 32-byte region [ffff888XXXXXXXXX, ffff888XXXXXXXXX)\n\n  Breakdown:\n    62 slab-out-of-bounds (reads + writes past allocation)\n     7 slab-use-after-free\n     4 use-after-free\n\nAll credit to Stan for the wonderful description and reproducer!\n\n[sean: write changelog]"}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"4af663c2f64a8d252e690c60cf8b8abf22dc2951","status":"affected","lessThan":"bf9ba093fbb83c0c9a3dedd50efec29424eca2fc","versionType":"git"},{"version":"4af663c2f64a8d252e690c60cf8b8abf22dc2951","status":"affected","lessThan":"c9b4198fbc6ed99a9da4bee9f74bb730f926c9ae","versionType":"git"},{"version":"4af663c2f64a8d252e690c60cf8b8abf22dc2951","status":"affected","lessThan":"b328ede59ac34e7998e1eee5e5f0cc26c2a91846","versionType":"git"},{"version":"4af663c2f64a8d252e690c60cf8b8abf22dc2951","status":"affected","lessThan":"db3f2195d29344a3cf1e9dd9ab7f21ced7308cf7","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["arch/x86/kvm/svm/sev.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.10","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.10","versionType":"semver"},{"version":"6.12.93","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.35","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.0.12","status":"unaffected","lessThanOrEqual":"7.0.*","versionType":"semver"},{"version":"7.1","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["arch/x86/kvm/svm/sev.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/bf9ba093fbb83c0c9a3dedd50efec29424eca2fc"},{"url":"https://git.kernel.org/stable/c/c9b4198fbc6ed99a9da4bee9f74bb730f926c9ae"},{"url":"https://git.kernel.org/stable/c/b328ede59ac34e7998e1eee5e5f0cc26c2a91846"},{"url":"https://git.kernel.org/stable/c/db3f2195d29344a3cf1e9dd9ab7f21ced7308cf7"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H","baseScore":8.8,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - The vulnerable path is reached by running a SEV-SNP vCPU through KVM and issuing a guest-controlled VMGEXIT PSC request, not by remote packets or adjacent/physical access.\nAC:L - The guest directly controls the scratch pointer/length and PSC entry bounds, and can repeatedly issue malformed VMGEXITs without needing external races or rare timing conditions.\nPR:L - Exploitation requires the ability to run or control a SEV-SNP guest/KVM vCPU, which is a low-privilege local or tenant capability rather than real host root in the init namespace.\nUI:N - Once the attacker controls the malicious guest or VM process, no additional victim action is required to trigger the VMGEXIT handling path.\nS:C - The bug lets a malicious guest corrupt and disclose host kernel heap memory, crossing the guest-to-host virtualization security boundary.\nC:H - The OOB reads and error oracle leak adjacent host heap contents/layout, and the associated memory corruption/UAF behavior is sufficient to treat confidentiality impact as high.\nI:H - The vulnerable path performs OOB writes into adjacent host slab objects and can trigger UAF conditions, making host kernel memory corruption and potential control-flow compromise defensible.\nA:H - The bug produces host kernel slab OOB writes/reads and UAF reports and can crash or destabilize the host kernel, giving high availability impact."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-08-05T12:35:09.892Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.10","versionEndExcluding":"6.12.93"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.10","versionEndExcluding":"6.18.35"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.10","versionEndExcluding":"7.0.12"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"6.10","versionEndExcluding":"7.1"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-53360","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"no"},{"Technical Impact":"total"}],"version":"2.0.3","timestamp":"2026-10-16T15:29:05.458760Z"}}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-787","lang":"en","type":"CWE","description":"CWE-787 Out-of-bounds Write"}]}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-19T20:07:44.426Z"}}]}}}