CVE-2026-63794: KVM: SVM: Fix page overflow in sev_dbg_crypt() for ENCRYPT path

High 7.8 EPSS 0.1% Linux kernel

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: <TASK> 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 </TASK> 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@]

• CVE-2026-63794CVE identifier
• 7.8CVSS 3.1 base score (high)
• 0.1%EPSS: chance of exploitation in the next 30 days (higher than 4% of CVEs)
• 2026-07-19published

What do these terms mean? CVE · CVSS score · exploited (KEV) · EPSS · backported fix · all terms

Affected and fixed versions

Affected:

• Linux Linux 24f41fb23a39bc2b6f190dcef35a5813a4bf183a to before f701ae476cb92a3a3d8844bb39bb63b4512684c8
• Linux Linux 24f41fb23a39bc2b6f190dcef35a5813a4bf183a to before 64f2449841ffc7d203183aa4c748c9c77951ecc5
• Linux Linux 24f41fb23a39bc2b6f190dcef35a5813a4bf183a to before 9349b50f4b11f135fe73b56cb2c2c872d8bc71d7
• Linux Linux 24f41fb23a39bc2b6f190dcef35a5813a4bf183a to before 889c2a9c59897ca912bf39df5bb92555a0a13df4
• Linux Linux 24f41fb23a39bc2b6f190dcef35a5813a4bf183a to before e1a0fe288dee07b7da25a71e007c1ecd1080315b
• Linux Linux 24f41fb23a39bc2b6f190dcef35a5813a4bf183a to before 720949ed666f34ff28ffdfe1471a5861d1e41fdf
• Linux Linux 24f41fb23a39bc2b6f190dcef35a5813a4bf183a to before 2753a097d1fe24c4351c608048612c74108aa89f
• Linux Linux 24f41fb23a39bc2b6f190dcef35a5813a4bf183a to before 78ee2d50185a037b3d2452a97f3dad69c3f7f389
• Linux Linux 4.16

Patch it

Use the commands for your system. Distribution packages often keep an older version number with the fix backported, so compare with the fixed package versions in the table below, not only with the upstream version.

sudo apt update
sudo apt install --only-upgrade linux-image-amd64

sudo apt update
sudo apt install --only-upgrade linux-image-generic (or the installed flavour: linux-image-aws, -azure, -gcp, -virtual)

sudo dnf upgrade --refresh kernel

sudo dnf upgrade --refresh kernel

sudo zypper refresh
sudo zypper update kernel-default

sudo dnf upgrade --releasever=latest kernel kernel6.12

sudo pacman -Syu

apk update && apk upgrade linux-lts linux-virt

not Linux

General update steps for every system are on the Linux and Unix & BSD pages; after updating, see which services to restart.

Fix status in Linux distributions

From the Debian security tracker, Ubuntu CVE tracker and Red Hat Security Data API, refreshed every few hours.

Sources

• https://git.kernel.org/stable/c/f701ae476cb92a3a3d8844bb39bb63b4512684c8
• https://git.kernel.org/stable/c/64f2449841ffc7d203183aa4c748c9c77951ecc5
• https://git.kernel.org/stable/c/9349b50f4b11f135fe73b56cb2c2c872d8bc71d7
• https://git.kernel.org/stable/c/889c2a9c59897ca912bf39df5bb92555a0a13df4
• https://git.kernel.org/stable/c/e1a0fe288dee07b7da25a71e007c1ecd1080315b
• https://git.kernel.org/stable/c/720949ed666f34ff28ffdfe1471a5861d1e41fdf
• https://git.kernel.org/stable/c/2753a097d1fe24c4351c608048612c74108aa89f
• https://git.kernel.org/stable/c/78ee2d50185a037b3d2452a97f3dad69c3f7f389
• CVE-2026-63794 on CVE.org
• CVE-2026-63794 on NVD

Page generated automatically from official sources on 2026-11-03 18:05 UTC. Always confirm with your vendor's advisory.