In the Linux kernel, the following vulnerability has been resolved:
btrfs: do not ASSERT() if the newly created subvolume already got read
[BUG]
There is a syzbot crash, triggered by the ASSERT() during subvolume
creation:
assertion failed: !anon_dev, in fs/btrfs/disk-io.c:1319
------------[ cut here ]------------
kernel BUG at fs/btrfs/disk-io.c:1319!
invalid opcode: 0000 [#1] PREEMPT SMP KASAN
RIP: 0010:btrfs_get_root_ref.part.0+0x9aa/0xa60
btrfs_get_new_fs_root+0xd3/0xf0
create_subvol+0xd02/0x1650
btrfs_mksubvol+0xe95/0x12b0
__btrfs_ioctl_snap_create+0x2f9/0x4f0
btrfs_ioctl_snap_create+0x16b/0x200
btrfs_ioctl+0x35f0/0x5cf0
__x64_sys_ioctl+0x19d/0x210
do_syscall_64+0x3f/0xe0
entry_SYSCALL_64_after_hwframe+0x63/0x6b
---[ end trace 0000000000000000 ]---
[CAUSE]
During create_subvol(), after inserting root item for the newly created
subvolume, we would trigger btrfs_get_new_fs_root() to get the
btrfs_root of that subvolume.
The idea here is, we have preallocated an anonymous device number for
the subvolume, thus we can assign it to the new subvolume.
But there is really nothing preventing things like backref walk to read
the new subvolume.
If that happens before we call btrfs_get_new_fs_root(), the subvolume
would be read out, with a new anonymous device number assigned already.
In that case, we would trigger ASSERT(), as we really expect no one to
read out that subvolume (which is not yet accessible from the fs).
But things like backref walk is still possible to trigger the read on
the subvolume.
Thus our assumption on the ASSERT() is not correct in the first place.
[FIX]
Fix it by removing the ASSERT(), and just free the @anon_dev, reset it
to 0, and continue.
If the subvolume tree is read out by something else, it should have
already get a new anon_dev assigned thus we only need to free the
preallocated one.
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (5.5): severity, escalated by confirmed exploitation. This CVE's 5.5 is its impact severity (EG Severity), not escalated.
- EG Severity
- 5.5 MEDIUMCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
- EG Likelihood
- 0.2% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-25). FIRST's exploitation probability, not an EchelonGraph model.
- Confirmed exploitation
- None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
- EG Priority
- SSVC Track at medium mission impactTrack at every mission impact level.CISA BOD 26-04: 60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.
SSVC (CISA's decision table, applied by EchelonGraph)Track at every mission impact level.
A fix is available. Apply it within your standard update timelines.
Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table
BOD 26-04 (CISA's remediation timeline, Table 1)60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.
The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it