--- id: CVE-2026-63794 title: |- In the Linux kernel, the following vulnerability has been resolved: KVM: SVM: Fix page overflow in sev_dbg_crypt() for ENCRYPT path In sev_dbg_crypt(), the per-iteration transfer length is bounded by the source page offset (PAGE_SIZE -… summary: |- In the Linux kernel, the following vulnerability has been resolved: KVM: SVM: Fix page overflow in sev_dbg_crypt() for ENCRYPT path In sev_dbg_crypt(), the per-iteration transfer length is bounded by the source page offset (PAGE_SIZE -… severity: high published: '2026-07-19' updated: '2026-07-19' source: NVD sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-63794' references: - url: 'https://git.kernel.org/stable/c/2753a097d1fe24c4351c608048612c74108aa89f' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/64f2449841ffc7d203183aa4c748c9c77951ecc5' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/720949ed666f34ff28ffdfe1471a5861d1e41fdf' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/78ee2d50185a037b3d2452a97f3dad69c3f7f389' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/889c2a9c59897ca912bf39df5bb92555a0a13df4' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/9349b50f4b11f135fe73b56cb2c2c872d8bc71d7' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/e1a0fe288dee07b7da25a71e007c1ecd1080315b' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: 'https://git.kernel.org/stable/c/f701ae476cb92a3a3d8844bb39bb63b4512684c8' label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 - url: >- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63794.json - url: 'https://access.redhat.com/security/cve/CVE-2026-63794' - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2502241' - url: 'https://www.cve.org/CVERecord?id=CVE-2026-63794' - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-63794' - url: >- https://lore.kernel.org/linux-cve-announce/2026071959-CVE-2026-63794-b463@gregkh/T - url: 'https://access.redhat.com/errata/RHSA-2026:74438' - url: 'https://access.redhat.com/errata/RHSA-2026:76738' - url: 'https://access.redhat.com/errata/RHSA-2026:75747' - url: 'https://access.redhat.com/errata/RHSA-2026:75746' tags: - nvd - csaf - vex - red-hat ingestedAt: '2026-07-19T23:34:10.623Z' epss: 0.00142 epssPercentile: 0.03485 vendor: Red Hat product: Red Hat Enterprise Linux BaseOS (v. 9) affected: - enterprise_linux 10 - enterprise_linux 8 - enterprise_linux 9 - enterprise_linux_appstream_v_9 - enterprise_linux_baseos_v_9 - enterprise_linux_codeready_linux_builder_v_9 - enterprise_linux_real_time_for_nfv_v_9 - enterprise_linux_real_time_v_9 patched: - enterprise_linux_appstream_v_9 - enterprise_linux_baseos_v_9 - enterprise_linux_codeready_linux_builder_v_9 - enterprise_linux_real_time_for_nfv_v_9 - enterprise_linux_real_time_v_9 cvss: 7 cvssVector: 'CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H' cvssSource: vendor cwe: - CWE-805 --- ## Overview In the Linux kernel, the following vulnerability has been resolved: KVM: SVM: Fix page overflow in sev_dbg_crypt() for ENCRYPT path In sev_dbg_crypt(), the per-iteration transfer length is bounded by the source page offset (PAGE_SIZE - s_off) but not by the destination page offset (PAGE_SIZE - d_off). When d_off > s_off, the encrypt path (__sev_dbg_encrypt_user) performs a read-modify-write using a single-page intermediate buffer (dst_tpage): 1. __sev_dbg_decrypt() expands the size to round_up(len + (d_off & 15), 16) before issuing the PSP command. If len + (d_off & 15) > PAGE_SIZE, the PSP writes beyond the end of the 4096-byte dst_tpage allocation. 2. The subsequent memcpy()/copy_from_user() into page_address(dst_tpage) + (d_off & 15) of 'len' bytes overflows by up to 15 bytes under the same condition. Trigger example: s_off = 0, d_off = 1, debug.len = PAGE_SIZE - the PSP is instructed to write round_up(4097, 16) = 4112 bytes to a 4096-byte buffer. Fix by also bounding len by (PAGE_SIZE - d_off), the same check that sev_send_update_data() already performs for its single-page guest region. ================================================================== BUG: KASAN: slab-use-after-free in sev_dbg_crypt+0x993/0xd10 [kvm_amd] Write of size 4095 at addr ff110062293bb009 by task sev_dbg_test/228214 CPU: 96 UID: 0 PID: 228214 Comm: sev_dbg_test Tainted: G U W 7.0.0-smp--5ce9b0c48211-dbg #156 PREEMPTLAZY Tainted: [U]=USER, [W]=WARN Hardware name: Google Astoria/astoria, BIOS 0.20250817.1-0 08/25/2025 Call Trace: dump_stack_lvl+0x54/0x70 print_report+0xbc/0x260 kasan_report+0xa2/0xd0 kasan_check_range+0x25f/0x2c0 __asan_memcpy+0x40/0x70 sev_dbg_crypt+0x993/0xd10 [kvm_amd] sev_mem_enc_ioctl+0x33c/0x450 [kvm_amd] kvm_vm_ioctl+0x65d/0x6d0 [kvm] __se_sys_ioctl+0xb2/0x100 do_syscall_64+0xe8/0x870 entry_SYSCALL_64_after_hwframe+0x4b/0x53 The buggy address belongs to the physical page: page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x7fe72b6a0 pfn:0x62293bb memcg:ff11000112827d82 flags: 0x1400000000000000(node=1|zone=1) raw: 1400000000000000 0000000000000000 dead000000000122 0000000000000000 raw: 00000007fe72b6a0 0000000000000000 00000001ffffffff ff11000112827d82 page dumped because: kasan: bad access detected Memory state around the buggy address: ff110062293bbf00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ff110062293bbf80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 >ff110062293bc000: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ^ ff110062293bc080: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ff110062293bc100: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ================================================================== Disabling lock debugging due to kernel taint [sean: add sample KASAN splat, Fixes, and stable@] ## Remediation Refer to the linked advisories for vendor-supplied fixes and affected version ranges. ## Vendor advisories - **RHSA-2026:74438** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream (v. 9), Red Hat Enterprise Linux BaseOS (v. 9), Red Hat Enterprise Linux CodeReady Linux Builder (v. 9), Red Hat Enterprise Linux Real Time for NFV (v. 9), Red Hat Enterprise Linux Real Time (v. 9) · released 2026-10-02 · [advisory](https://access.redhat.com/errata/RHSA-2026:74438) - **Red Hat VEX** · Moderate · affected: Red Hat Enterprise Linux 9 · no fix planned: Red Hat Enterprise Linux 9 · updated 2026-10-26 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63794.json) - **RHSA-2026:76738** · Red Hat · fixed in: 10Base-SMTV, Red Hat Enterprise Linux AppStream (v. 10), Red Hat Enterprise Linux BaseOS (v. 10), Red Hat Enterprise Linux CodeReady Linux Builder (v. 10), Red Hat Enterprise Linux Hidden (v. 10), Red Hat Enterprise Linux Real Time for NFV (v. 10), … · released 2026-10-08 · [advisory](https://access.redhat.com/errata/RHSA-2026:76738) - **RHSA-2026:75747** · Red Hat · fixed in: Red Hat Enterprise Linux BaseOS (v. 8), Red Hat Enterprise Linux CRB (v. 8) · released 2026-10-05 · [advisory](https://access.redhat.com/errata/RHSA-2026:75747) - **RHSA-2026:75746** · Red Hat · fixed in: Red Hat Enterprise Linux NFV (v. 8), Red Hat Enterprise Linux RT (v. 8) · released 2026-10-05 · [advisory](https://access.redhat.com/errata/RHSA-2026:75746)