{"id":"CVE-2026-89793","published":"2026-09-16T10:16:55.173","lastModified":"2026-09-16T15:18:09.510","description":"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.","cvssScore":7.8,"cvssSeverity":"HIGH","cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","cwes":[],"vendors":[],"products":[],"references":[{"url":"https://git.kernel.org/stable/c/5befd06a72216869b607cf7724a4f16c6a2d3999","tags":[]},{"url":"https://git.kernel.org/stable/c/6e2b571b0a54755b06e092501913e1dfefe75d6c","tags":[]},{"url":"https://git.kernel.org/stable/c/be41733c24be58e2a1ef718c80fafdfb98a40d5e","tags":[]},{"url":"https://git.kernel.org/stable/c/e373c1acdbcf88cec533ece9f589020adaed0a78","tags":[]},{"url":"https://git.kernel.org/stable/c/fa5e1bc673ca59722608af67b27e65dba0c97926","tags":[]}],"exploitRefs":[],"hasPoc":false,"ai":null}