{"id":"CVE-2026-64456","revision":"2902146d2cc14094a4561f5f469c7a40","records":[{"revision":"2902146d2cc14094a4561f5f469c7a40","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-64456","aliases":[],"title":"hwrng: virtio: clamp device-reported used.len at copy_data()","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nhwrng: virtio: clamp device-reported used.len at copy_data()\n\nrandom_recv_done() stores the device-reported used.len directly into\nvi->data_avail.  copy_data() then indexes vi->data[] using\nvi->data_idx (advanced by previous copy_data() calls) and issues a\nmemcpy() without re-validating either value against the posted\nbuffer size sizeof(vi->data) (SMP_CACHE_BYTES bytes, typically 32\nor 64).\n\nA malicious or buggy virtio-rng backend can set used.len beyond\nsizeof(vi->data), steering the memcpy() past the end of the inline\narray into adjacent kmalloc-1k slab bytes.  hwrng_fillfn() mixes\nthose bytes into the guest RNG, and guest root can also observe\nthem directly via /dev/hwrng.\n\nConcrete impact is inside the guest:\n\n - Memory-safety / hardening: any virtio-rng backend that\n   over-reports used.len causes the driver to read past vi->data\n   into unrelated slab contents.  hwrng_fillfn() is a kernel thread\n   that runs as soon as the device is probed; no guest userspace\n   interaction is required to first-trigger the OOB.\n\n - Cross-boundary leak (confidential-compute threat model): a\n   malicious hypervisor cooperating with a malicious or compromised\n   guest root userspace can use /dev/hwrng as a leak channel for\n   guest-kernel heap data.  The host sets a large used.len, guest\n   root reads /dev/hwrng, and the returned bytes contain guest\n   kernel slab contents that were adjacent to vi->data.  In\n   practice, confidential-compute guests (SEV-SNP, TDX) usually\n   disable virtio-rng entirely, so this path is narrow, but the\n   fix is still worth carrying because the underlying\n   memory-safety bug contaminates the guest RNG on any host.\n\nKASAN confirms the OOB on a 7.1-rc4 guest whose virtio-rng backend\nhas been patched to report used.len = 0x10000:\n\n  BUG: KASAN: slab-out-of-bounds in virtio_read+0x394/0x5d0\n  Read of size 64 at addr ffff88800ae0ba20 by task hwrng/52\n  Call Trace:\n   __asan_memcpy+0x23/0x60\n   virtio_read+0x394/0x5d0\n   hwrng_fillfn+0xb2/0x470\n   kthread+0x2cc/0x3a0\n  Allocated by task 1:\n   probe_common+0xa5/0x660\n   virtio_dev_probe+0x549/0xbc0\n  The buggy address belongs to the object at ffff88800ae0b800\n   which belongs to the cache kmalloc-1k of size 1024\n  The buggy address is located 0 bytes to the right of\n   allocated 544-byte region [ffff88800ae0b800, ffff88800ae0ba20)\n\nSame class of bug as commit c04db81cd028 (\"net/9p: Fix buffer\noverflow in USB transport layer\"), which hardened\nusb9pfs_rx_complete() against unchecked device-reported length in\nthe USB 9p transport.\n\nWith the clamp at point of use and array_index_nospec() in place,\nthe same harness boots cleanly: copy_data() returns zero for the\nbogus report, the device-supplied bytes after data_idx are\ndiscarded, and the driver issues a fresh request.","state":0,"publishedAt":"2026-07-25T08:51:24.659+00:00","modifiedAt":"2026-10-19T20:38:30.595+00:00","affected":[{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"product\": \"Linux\",\n                    \"vendor\": \"Linux\",\n                    \"defaultStatus\": \"unaffected\",\n                    \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n                    \"programFiles\": [\n                        \"drivers/char/hw_random/virtio-rng.c\"\n                    ],\n                    \"versions\": [\n                        {\n                            \"version\": \"f7f510ec195781c857ab76366a3e1c59e1caae42\",\n                            \"lessThan\": \"3aa3e89cf80721c8d382b4c1a2b70a0449dad4a5\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"f7f510ec195781c857ab76366a3e1c59e1caae42\",\n                            \"lessThan\": \"63335e7b638ae70028ae285bb95153874a8bc852\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"f7f510ec195781c857ab76366a3e1c59e1caae42\",\n                            \"lessThan\": \"2e788948ff2a13358a303af112497a63201c5739\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"f7f510ec195781c857ab76366a3e1c59e1caae42\",\n                            \"lessThan\": \"fde19b0d4eeabae042519313c843fe6f27d41e9d\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"f7f510ec195781c857ab76366a3e1c59e1caae42\",\n                            \"lessThan\": \"81dd21b5f0c299cc7b5bf84f04a61938559d20e6\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"f7f510ec195781c857ab76366a3e1c59e1caae42\",\n                            \"lessThan\": \"285e17c44e3873a73460f294acbd64018ff64385\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"f7f510ec195781c857ab76366a3e1c59e1caae42\",\n                            \"lessThan\": \"92d5736a62040ec1cfff23ea57e6599301690ad5\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"f7f510ec195781c857ab76366a3e1c59e1caae42\",\n                            \"lessThan\": \"e3046eeada299f917a8ad883af4434bfb86556b1\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        }\n                    ]\n                }"},{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"product\": \"Linux\",\n                    \"vendor\": \"Linux\",\n                    \"defaultStatus\": \"affected\",\n                    \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n                    \"programFiles\": [\n                        \"drivers/char/hw_random/virtio-rng.c\"\n                    ],\n                    \"versions\": [\n                        {\n                            \"version\": \"2.6.26\",\n                            \"status\": \"affected\"\n                        },\n                        {\n                            \"version\": \"0\",\n                            \"lessThan\": \"2.6.26\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"5.10.261\",\n                            \"lessThanOrEqual\": \"5.10.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"5.15.212\",\n                            \"lessThanOrEqual\": \"5.15.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.1.178\",\n                            \"lessThanOrEqual\": \"6.1.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.6.145\",\n                            \"lessThanOrEqual\": \"6.6.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.12.96\",\n                            \"lessThanOrEqual\": \"6.12.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.18.39\",\n                            \"lessThanOrEqual\": \"6.18.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"7.1.4\",\n                            \"lessThanOrEqual\": \"7.1.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"7.2\",\n                            \"lessThanOrEqual\": \"*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"original_commit_for_fix\"\n                        }\n                    ]\n                }"}],"metrics":[{"system":"CVSS 3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H","score":7.7,"severity":"HIGH"}],"references":["https://git.kernel.org/stable/c/3aa3e89cf80721c8d382b4c1a2b70a0449dad4a5","https://git.kernel.org/stable/c/63335e7b638ae70028ae285bb95153874a8bc852","https://git.kernel.org/stable/c/2e788948ff2a13358a303af112497a63201c5739","https://git.kernel.org/stable/c/fde19b0d4eeabae042519313c843fe6f27d41e9d","https://git.kernel.org/stable/c/81dd21b5f0c299cc7b5bf84f04a61938559d20e6","https://git.kernel.org/stable/c/285e17c44e3873a73460f294acbd64018ff64385","https://git.kernel.org/stable/c/92d5736a62040ec1cfff23ea57e6599301690ad5","https://git.kernel.org/stable/c/e3046eeada299f917a8ad883af4434bfb86556b1"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-64456","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-64456","identifiers":["CVE-2026-64456"]},"retained":false,"historicalAffected":[]}],"coverage":[]}