{"id":"CVE-2026-89793","title":"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-o…","summary":"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-o…","severity":"high","cvss":7.8,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","vendor":"Linux","product":"Linux","affected":["Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < be41733c24be58e2a1ef718c80fafdfb98a40d5e","Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 5befd06a72216869b607cf7724a4f16c6a2d3999","Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < e373c1acdbcf88cec533ece9f589020adaed0a78","Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < fa5e1bc673ca59722608af67b27e65dba0c97926","Linux >= 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 < 6e2b571b0a54755b06e092501913e1dfefe75d6c","Linux < 6.6.157","Linux < 6.12.110","Linux < 6.18.51","Linux < 7.2.5","Linux (all versions)"],"published":"2026-09-16","updated":"2026-09-16","sourceUpdated":"2026-09-16T15:18:09.510","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-89793","references":[{"url":"https://git.kernel.org/stable/c/5befd06a72216869b607cf7724a4f16c6a2d3999","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/6e2b571b0a54755b06e092501913e1dfefe75d6c","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/be41733c24be58e2a1ef718c80fafdfb98a40d5e","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/e373c1acdbcf88cec533ece9f589020adaed0a78","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/fa5e1bc673ca59722608af67b27e65dba0c97926","label":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"}],"tags":["nvd","cve.org"],"ingestedAt":"2026-09-16T10:53:53.925Z","epss":0.00163,"epssPercentile":0.05975,"slug":"CVE-2026-89793","body":"## Overview\n\nIn 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.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":43,"depthScoreParts":{"impact":42.9,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[{"seq":205257,"id":"CVE-2026-89793","ts":1789570705960,"field":"cvss","old":null,"new":"7.8"},{"seq":205256,"id":"CVE-2026-89793","ts":1789570705960,"field":"severity","old":"none","new":"high"}]}