{"cve":"CVE-2026-53360","nvd":{"published":"2026-07-04T12:17:01.880","modified":"2026-10-19T20:19:16.147","status":"Modified","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]","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H","score":8.8},"cwes":["CWE-125","CWE-787"],"references":["https://git.kernel.org/stable/c/b328ede59ac34e7998e1eee5e5f0cc26c2a91846","https://git.kernel.org/stable/c/bf9ba093fbb83c0c9a3dedd50efec29424eca2fc","https://git.kernel.org/stable/c/c9b4198fbc6ed99a9da4bee9f74bb730f926c9ae","https://git.kernel.org/stable/c/db3f2195d29344a3cf1e9dd9ab7f21ced7308cf7"],"products":["linux:linux_kernel"],"source":"nvd","synced_at":"2026-10-21T03:43:09.190223697+00:00"},"epss":{"cve":"CVE-2026-53360","score":0.00297,"percentile":0.22162,"date":"2026-10-25"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}