ublk: clear VM_MAYWRITE on read-only ublk char device mmap (CVE-2026-89793) | HOL Guard CVE

Unknown severity · Source severity not reportedCVE-2026-89793

ublk: clear VM_MAYWRITE on read-only ublk char device mmap

Answer in brief

CVE-2026-89793 records a Unknown severity vulnerability in ublk: clear VM_MAYWRITE on read-only ublk char device mmap. The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 16, 2026Updated Sep 16, 2026Source checked Sep 16, 2026First seen by HOL Sep 16, 2026Material review Sep 16, 2026

Upstream Advisory

Key facts

Risk: Unknown severitySource severity not reported
Exploitation: Not marked as known exploited
Affected software: 1 mapped package or product
Fix availability: Available

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Linux/Linux (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
Linux/Linuxgeneric	>=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <be41733c24be58e2a1ef718c80fafdfb98a40d5e \|\| >=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <5befd06a72216869b607cf7724a4f16c6a2d3999 \|\| >=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <e373c1acdbcf88cec533ece9f589020adaed0a78 \|\| >=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <fa5e1bc673ca59722608af67b27e65dba0c97926 \|\| >=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <6e2b571b0a54755b06e092501913e1dfefe75d6c \|\| >=0 <6.6.157 \|\| >=0 <6.12.110 \|\| >=0 <6.18.51 \|\| >=0 <7.2.5	be41733c24be58e2a1ef718c80fafdfb98a40d5e, 5befd06a72216869b607cf7724a4f16c6a2d3999, e373c1acdbcf88cec533ece9f589020adaed0a78, fa5e1bc673ca59722608af67b27e65dba0c97926, 6e2b571b0a54755b06e092501913e1dfefe75d6c, 6.6.157, 6.12.110, 6.18.51, 7.2.5

Recommended response

Check inventory. Check lockfiles and deployed manifests for Linux/Linux.
Review the reported fix. Update Linux/Linux to be41733c24be58e2a1ef718c80fafdfb98a40d5e if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Sep 16, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 16, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Sep 16, 2026

Sources and claim methodology

Upstream source description

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.

Quoted source text, attributed separately from HOL analysis.