{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-89793", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-09-11T19:38:34.766Z", "datePublished": "2026-09-16T09:54:33.678Z", "dateUpdated": "2026-10-19T08:52:48.148Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-10-19T08:52:48.148Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nublk: clear VM_MAYWRITE on read-only ublk char device mmap\n\nublk_ch_mmap() rejects mmap requests with VM_WRITE set, but never\nclears VM_MAYWRITE on the resulting read-only mapping. This allows\na userspace daemon to mmap the per-queue command buffer PROT_READ,\nthen upgrade it to PROT_WRITE via mprotect(), since VM_MAYWRITE was\nnever cleared.\n\nThe command buffer holds struct ublksrv_io_desc entries that are\nkernel-written ABI; a writable mapping lets an unprivileged daemon\nprocess corrupt fields such as addr, op_flags, nr_sectors, and\nstart_sector.\n\nSame bug class as the drm/panthor and drm/vc4 VM_MAYWRITE fixes, and\nthe 2026-08-13 ptp/vmclock fix (a5edadbae57e).\n\nVerified via mprotect() PoC: before the fix, a PROT_READ mapping can\nbe upgraded to PROT_READ|PROT_WRITE and a write into the command\nbuffer corrupts io_desc fields (confirmed under KASAN). After the\nfix, mprotect() returns -EACCES." } ], "metrics": [ { "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "baseScore": 7.8, "baseSeverity": "HIGH" }, "scenarios": [ { "lang": "en", "value": "AV:L - The bug is reached only through local syscalls: open of /dev/ublkcN (created via /dev/ublk-control), mmap(PROT_READ) of the per-queue command buffer in ublk_ch_mmap(), then mprotect(PROT_WRITE). There is no network, Bluetooth, or physical-bus path into this mmap handler.\nAC:L - The attacker fully controls every step: mmap PROT_READ, mprotect PROT_WRITE, and write through the remap_pfn_range PFNMAP. mprotect upgrades the VMA because VM_MAYWRITE was left set (mm/mprotect.c), with no race, special layout, or victim state required.\nPR:L - ublk_ctrl_add_dev() lets a caller without CAP_SYS_ADMIN create a device with UBLK_F_UNPRIVILEGED_DEV, and ublk_ch_open() has no capability check, so an ordinary local user or a delegated unprivileged ublk daemon can open /dev/ublkcN and mmap the command buffer.\nUI:N - The attacking process performs the full create/open/mmap/mprotect/write sequence itself and can issue I/O to its own ublk disk to drive kernel re-reads of the corrupted descriptors. No other user must mount, open, or otherwise interact.\nS:U - The corrupted io_cmd_buf pages and the ublk/block I/O path that consumes them all sit in the host kernel's security authority. This is standard local kernel memory corruption, not a VM, IOMMU, or hypervisor boundary escape.\nC:H - The kernel re-reads iod->op_flags via ublk_iod_is_shmem_zc() on completion; setting UBLK_IO_F_SHMEM_ZC skips ublk_unmap_io(), so READ bios complete with uninitialized request/page-cache pages. That is the same uninitialized kernel-memory leak UBLK_F_SUPPORT_ZERO_COPY was denied to unprivileged devices to prevent.\nI:H - After mprotect, userspace has a writable PFNMAP of kernel-allocated io_cmd_buf pages and can overwrite kernel-written ublksrv_io_desc fields (op_flags, addr, nr_sectors, start_sector). The kernel then trusts op_flags to skip map/unmap, corrupting the block I/O data path for every consumer of that ublk disk.\nA:H - Clearing SHMEM_ZC with a null io->buf.addr forces ublk_start_io() into the mapped_bytes==0 requeue loop and stalls the request queue; completing I/O against corrupted descriptors or uninitialized pages can oops or hang the kernel. Attacker-triggerable kernel hang or crash is High." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "drivers/block/ublk_drv.c" ], "versions": [ { "version": "71f28f3136aff5890cd56de78abc673f8393cad9", "lessThan": "be41733c24be58e2a1ef718c80fafdfb98a40d5e", "status": "affected", "versionType": "git" }, { "version": "71f28f3136aff5890cd56de78abc673f8393cad9", "lessThan": "5befd06a72216869b607cf7724a4f16c6a2d3999", "status": "affected", "versionType": "git" }, { "version": "71f28f3136aff5890cd56de78abc673f8393cad9", "lessThan": "e373c1acdbcf88cec533ece9f589020adaed0a78", "status": "affected", "versionType": "git" }, { "version": "71f28f3136aff5890cd56de78abc673f8393cad9", "lessThan": "fa5e1bc673ca59722608af67b27e65dba0c97926", "status": "affected", "versionType": "git" }, { "version": "71f28f3136aff5890cd56de78abc673f8393cad9", "lessThan": "6e2b571b0a54755b06e092501913e1dfefe75d6c", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "drivers/block/ublk_drv.c" ], "versions": [ { "version": "6.0", "status": "affected" }, { "version": "0", "lessThan": "6.0", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.157", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.110", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.51", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.2.5", "lessThanOrEqual": "7.2.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.3", "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": "6.0", "versionEndExcluding": "6.6.157" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.0", "versionEndExcluding": "6.12.110" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.0", "versionEndExcluding": "6.18.51" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.0", "versionEndExcluding": "7.2.5" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.0", "versionEndExcluding": "7.3" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/be41733c24be58e2a1ef718c80fafdfb98a40d5e" }, { "url": "https://git.kernel.org/stable/c/5befd06a72216869b607cf7724a4f16c6a2d3999" }, { "url": "https://git.kernel.org/stable/c/e373c1acdbcf88cec533ece9f589020adaed0a78" }, { "url": "https://git.kernel.org/stable/c/fa5e1bc673ca59722608af67b27e65dba0c97926" }, { "url": "https://git.kernel.org/stable/c/6e2b571b0a54755b06e092501913e1dfefe75d6c" } ], "title": "ublk: clear VM_MAYWRITE on read-only ublk char device mmap", "x_generator": { "engine": "bippy-1.2.0" } } } }