{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-63937", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-07-19T07:54:57.022Z", "datePublished": "2026-07-19T14:55:34.554Z", "dateUpdated": "2026-08-05T12:37:24.499Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T12:37:24.499Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: SEV: Use READ_ONCE() when reading entries/indices from PSC buffer\n\nUse READ_ONCE() when reading entries/indices from the guest-accessible\nPage State Change buffer to defend against TOCTOU bugs.\n\nDon't bother with READ_ONCE()/WRITE_ONCE() for cases where KVM is writing\n(and not consuming the result!), as the guest isn't supposed to touch the\nbuffer while it's being processed. I.e. using READ_ONCE() is all about\nprotecting against misbehaving guests." } ], "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 - Exploitation requires code execution inside an SEV-SNP guest that issues VMGEXIT PSC events into the host KVM hypervisor; this is local access to the host kernel via a guest-controlled hypercall path, not a remote network protocol.\nAC:L - The attacker fully controls the guest-accessible PSC buffer and can trigger concurrent VMGEXITs or use multiple vCPUs to modify indices/entries between KVM's validation read and later use, reliably winning the TOCTOU race without depending on uncontrollable host conditions.\nPR:L - The attacker only needs the ability to run code in an SEV-SNP guest on a KVM host (e.g., a cloud confidential-computing tenant), not real root or capabilities in the host's init namespace.\nUI:N - No victim interaction is required beyond the attacker operating their own malicious guest workload; PSC VMGEXITs are triggered programmatically from guest code.\nS:C - The vulnerable code runs in the host hypervisor but is reached from an untrusted guest; successful exploitation crosses the VM security boundary and can alter host-managed SEV-SNP page-state (RMP) for guest physical addresses.\nC:H - TOCTOU manipulation of PSC entries/indices can bypass validation and drive KVM_HC_MAP_GPA_RANGE on unvalidated GPA ranges, potentially flipping pages between private and shared and disclosing encrypted guest (or host-visible) memory beyond what was checked.\nI:H - The same TOCTOU allows inflating combined page ranges and operations passed to userspace, enabling unauthorized modification of page encryption attributes and corrupting hypervisor-managed memory state via misdirected MAP_GPA_RANGE processing.\nA:H - Incorrect indices and out-of-sync buffer state can cause invalid hypervisor processing, kernel warnings/panics, or repeated disruption of the host's KVM/SEV-SNP path; memory-corruption-class TOCTOU bugs are scored at full availability impact when exploitability is uncertain." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "arch/x86/kvm/svm/sev.c" ], "versions": [ { "version": "9b54e248d2644be71cb394eb85f31ad99e023a05", "lessThan": "bd232801ef1d1fd985d2d4ca3cd1d888303ca86f", "status": "affected", "versionType": "git" }, { "version": "9b54e248d2644be71cb394eb85f31ad99e023a05", "lessThan": "b1dfaa6f7a957726a6800135be3659fbe4bbf2a4", "status": "affected", "versionType": "git" }, { "version": "9b54e248d2644be71cb394eb85f31ad99e023a05", "lessThan": "edbbe88f83b524434974e84808d3093199d67c24", "status": "affected", "versionType": "git" }, { "version": "9b54e248d2644be71cb394eb85f31ad99e023a05", "lessThan": "c8cc238093ca6c99267032f6cfe78f59389f3157", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "arch/x86/kvm/svm/sev.c" ], "versions": [ { "version": "6.11", "status": "affected" }, { "version": "0", "lessThan": "6.11", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.93", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.35", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.0.12", "lessThanOrEqual": "7.0.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.1", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.11", "versionEndExcluding": "6.12.93" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.11", "versionEndExcluding": "6.18.35" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.11", "versionEndExcluding": "7.0.12" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.11", "versionEndExcluding": "7.1" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/bd232801ef1d1fd985d2d4ca3cd1d888303ca86f" }, { "url": "https://git.kernel.org/stable/c/b1dfaa6f7a957726a6800135be3659fbe4bbf2a4" }, { "url": "https://git.kernel.org/stable/c/edbbe88f83b524434974e84808d3093199d67c24" }, { "url": "https://git.kernel.org/stable/c/c8cc238093ca6c99267032f6cfe78f59389f3157" } ], "title": "KVM: SEV: Use READ_ONCE() when reading entries/indices from PSC buffer", "x_generator": { "engine": "bippy-1.2.0" } } } }