High 7.8Published Sep 16, 2026

CVE-2026-89793ublk: clear VM_MAYWRITE on read-only ublk char device mmap

Updated under an hour ago (Oct 28, 2026, 3:23 AM ET)

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No exploitation reported and no EPSS estimate yet.

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Exploited in the last 30 days

In the Linux kernel, the following vulnerability has been resolved: ublk: clear VM_MAYWRITE on read-only ublk char device mmap ublk_ch_mmap() rejects mmap requests with VM_WRITE set, but never clears VM_MAYWRITE on the resulting read-only mapping. This allows a userspace daemon to mmap the per-queue command buffer PROT_READ, then upgrade it to PROT_WRITE via mprotect(), since VM_MAYWRITE was never cleared. The command buffer holds struct ublksrv_io_desc entries that are kernel-written ABI; a writable mapping lets an unprivileged daemon process corrupt fields such as addr, op_flags, nr_sectors, and start_sector. Same bug class as the drm/panthor and drm/vc4 VM_MAYWRITE fixes, and the 2026-08-13 ptp/vmclock fix (a5edadbae57e). Verified via mprotect() PoC: before the fix, a PROT_READ mapping can be upgraded to PROT_READ|PROT_WRITE and a write into the command buffer corrupts io_desc fields (confirmed under KASAN). After the fix, mprotect() returns -EACCES.

CVSS: 7.8 HIGH (v3.1, CNA)CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Weakness (CWE): Not given
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: Linux
NVD analysis: Received
Record last updated: Oct 19, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

Linux Linux linux:linux (from the name)	from 71f28f3136aff5890cd56de78abc673f8393cad9 before be41733c24be58e2a1ef718c80fafdfb98a40d5e; 71f28f3136aff5890cd56de78abc673f8393cad9 builds before 5befd06a72216869b607cf7724a4f16c6a2d3999; from 71f28f3136aff5890cd56de78abc673f8393cad9 before e373c1acdbcf88cec533ece9f589020adaed0a78; from 71f28f3136aff5890cd56de78abc673f8393cad9 before fa5e1bc673ca59722608af67b27e65dba0c97926; 71f28f3136aff5890cd56de78abc673f8393cad9 builds before 6e2b571b0a54755b06e092501913e1dfefe75d6c	CNA record

References

References

https://git.kernel.org/stable/c/be41733c24be58e2a1ef718c80fafdfb98a40d5e
https://git.kernel.org/stable/c/5befd06a72216869b607cf7724a4f16c6a2d3999
https://git.kernel.org/stable/c/e373c1acdbcf88cec533ece9f589020adaed0a78
https://git.kernel.org/stable/c/fa5e1bc673ca59722608af67b27e65dba0c97926
https://git.kernel.org/stable/c/6e2b571b0a54755b06e092501913e1dfefe75d6c

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.