Look up another CVE · open CVE-2026-72367 in the interactive tracker
CVE-2026-72367
iomap: guard io_size EOF trim against concurrent truncate underflow
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem fs/iomap. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-72367 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 | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
iomap: fix zero padding data issue in concurrent append writes changed ioend accounting so that io_size tracks only valid data within EOF. This trims io_size when a writeback range extends past end_pos: ioend->io_size += map_len; if (ioend->io_offset + ioend->io_size > end_pos) ioend->io_size = end_pos - ioend->io_offset; However, if end_pos ends up below ioend->io_offset, the subtraction becomes negative and is stored in size_t io_size, causing an unsigned wrap to a huge value. This can happen when writeback continues past byte-level EOF up to a block-aligned range, or when a concurrent truncate shrinks the file after end_pos was sampled in iomap_writeback_handle_eof(). A wrapped io_size can mislead append detection and corrupt completion-time size handling, since filesystem end_io paths consume io_size for decisions such as on-disk EOF updates and unwritten/COW completion ranges. Fix this by clamping io_size to zero when EOF has moved to or before the ioend start offset. This preserves the original intent of trimming io_size to valid in-EOF data while avoiding the underflow.
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.
fs/iomap/ioend.c
- What this is
- FILESYSTEMS [IOMAP]MAINTAINERS section matched on fs/iomap/ · linux-xfs@vger.kernel.org · Supported
Check it on the machine
grep -wE 'CONFIG_BLOCK|CONFIG_FS_IOMAP' /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.
Show whether Debian builds this, per release
Debian builds this code. Every release with an answer below compiles the affected file into the kernels it ships. The build rule could not be established for 2 releases, so nothing is claimed about those.
- bookworm, trixie?
- forky, sidy
- ?
- not established - no Makefile entry for the affected file
- y
- built into the kernel image on every flavour - only a patch removes it
Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.
- Build switches
- CONFIG_BLOCK, CONFIG_FS_IOMAP
- Reads as
- all on means the file is compiled; any one off means it is not.
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
- 2026-08-15 (2 months ago)source
- CVSS
- 8.8 high
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.58%, higher than 46.6% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- fs/iomap
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.13 | 6.18.40 | 1f38f65bf965 |
| 6.13 | 7.1.5 | 7f7780abb4c0 |
| 6.13 | 7.2 | 55ec50d046c0 |
| 6.12.10 | 0 | 0 |
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:NAttack vector, network
- On XFS/GFS2/NTFS backends exposed via nfsd or ksmbd, a remote client can trigger iomap buffered writeback by issuing concurrent WRITE and truncate/SETATTR operations over the network without local shell access.
- AC:LAttack complexity, low
- The attacker controls both sides of the race by concurrently writing dirty pages and truncating the same file (local threads or parallel NFS/SMB requests); no uncontrollable memory layout or rare kernel configuration is required.
- PR:LPrivileges required, low
- Exploitation requires write and truncate permission on the target file (authenticated NFS/SMB client or local unprivileged user with file write access); this is not a pre-authentication network code path.
- UI:NUser interaction, none
- No victim interaction is needed beyond the attacker's own write and truncate I/O; writeback is driven automatically by the VFS/page-cache path once pages are dirtied.
- S:UScope, unchanged
- Impact is confined to kernel/filesystem integrity within the same security authority (metadata corruption, incorrect extent completion, possible local privilege escalation), not a VM escape or cross-authority boundary.
- C:HConfidentiality impact, high
- A wrapped io_size propagates into XFS completion paths (COW convert/end, unwritten conversion, append detection), potentially remapping or exposing unintended on-disk extents and data beyond the legitimate EOF-trimmed range.
- I:HIntegrity impact, high
- Huge bogus io_size drives xfs_reflink_convert_cow, xfs_reflink_end_cow, xfs_iomap_write_unwritten, and xfs_setfilesize with corrupted ranges, enabling incorrect on-disk metadata updates and file content modification.
- A:HAvailability impact, high
- Corrupted ioend accounting can trigger pathological XFS extent walks, ASSERT failures, filesystem shutdown, or hung writeback during I/O completion, causing kernel oops or sustained denial of service.