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CVE-2026-90324
ublk: check import_ubuf() return value
Published 2026-09-17 (31 days ago) by the Linux kernel CNA. Subsystem drivers/block. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-90324 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | vulnerable | 6.12.113-1 | No fix published anywhere yet, neither in Debian nor upstream for the series trixie tracks. Watch the Debian tracker page for this CVE. Advisories for trixie have historically landed a median of 11 days after publication. |
| Debian 14forky | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.6-1 | Update the kernel and reboot. Fixed in 7.2.6-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
import_ubuf() can fail if the address range (provided by the userspace ublk server) is outside the allowed user address space. Return that 0 bytes were copied if import_ubuf() fails rather than passing an uninitialized struct iov_iter to ublk_copy_user_pages().
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
drivers/block/ublk_drv.c
- What this is
- UBLK USERSPACE BLOCK DRIVERMAINTAINERS section matched on drivers/block/ublk_drv.c · linux-block@vger.kernel.org · Maintained
- Kernel module
- ublk_drv
Check it on the machine
grep -w CONFIG_BLK_DEV_UBLK /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
lsmod | grep -w ublk_drvPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian does not build this code in 1 release. It does build it in 3 releases, so the answer depends on which release the machine runs.
- bookwormn
- trixie, forky, sidm
- n
- not enabled on any flavour - this release does not build the code
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switch
- CONFIG_BLK_DEV_UBLK
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-09-17 (31 days ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.17%, higher than 6.3% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- drivers/block
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.5 | 6.18.52 | 0121c84adb6a |
| 6.5 | 7.2.6 | 5ac6019cb78e |
| 6.5 | 7.3 | 3831568792af |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- The bad pointer is io->buf.addr from ublksrv_io_cmd.addr in ublk_ch_uring_cmd_local() on UBLK_IO_FETCH_REQ, UBLK_IO_COMMIT_AND_FETCH_REQ, or UBLK_IO_NEED_GET_DATA against /dev/ublkcN. import_ubuf() in ublk_map_io()/ublk_unmap_io() is handed that local userspace address; no network protocol carries it.
- AC:LAttack complexity, low
- The ublk server chooses the FETCH/COMMIT buffer address. A non-zero kernel or wrap-around address fails access_ok() in import_ubuf() on every call (ublk_check_fetch_buf() only rejects addr==0). ublk_map_io()/ublk_unmap_io() then pass the uninitialized iov_iter to ublk_copy_user_pages() with no race or victim state.
- PR:LPrivileges required, low
- ublk_ctrl_add_dev() lets a caller without CAP_SYS_ADMIN create a UBLK_F_UNPRIVILEGED_DEV device, and those devices cannot set UBLK_F_USER_COPY, UBLK_F_SUPPORT_ZERO_COPY, or UBLK_F_AUTO_BUF_REG, so ublk_need_map_io() is always true. ublk_ch_open() has no capability check; ublk_open() allows the owner to issue I/O to /dev/ublkbN.
- UI:NUser interaction, none
- The attacking process itself issues UBLK_CMD_ADD_DEV and UBLK_CMD_START_DEV on /dev/ublk-control, UBLK_IO_FETCH_REQ with the bad addr on /dev/ublkcN, then read/write on its own ublkb disk so ublk_queue_rq() → ublk_cmd_tw_cb() → ublk_dispatch_req() runs. No other user must mount or open anything.
- S:UScope, unchanged
- ublk_copy_user_pages() copies between the ublk request bio pages and the confused iov_iter entirely inside the host kernel via _copy_to_iter()/_copy_from_iter(). This is local kernel memory corruption, not a VM, IOMMU, or hypervisor escape.
- C:HConfidentiality impact, high
- On a READ, ublk_unmap_io() calls _copy_from_iter() with the uninitialized iov_iter. iterate_and_advance() may treat leftover iter_type as ITER_KVEC or ITER_BVEC, so memcpy_from_iter() copies kernel memory into the request bio pages, which the attacker then reads from /dev/ublkbN.
- I:HIntegrity impact, high
- On a WRITE, ublk_map_io() calls _copy_to_iter() with that uninitialized iter, so iterate_kvec()/memcpy_to_iter() can write the attacker-controlled ublkb write payload to leftover kernel pointers. Garbage iter_type is iov_iter type confusion and an arbitrary kernel write.
- A:HAvailability impact, high
- iterate_kvec() loads p->iov_len from leftover kvec pointers and iterate_bvec() calls kmap_local_page() on leftover bv_page, either of which oopses. ublk_unmap_io() also hits WARN_ON_ONCE(!data_source) in _copy_from_iter() when the iter was left with data_source==0.