In the Linux kernel, the following vulnerability has been resolved:
btrfs: ensure no dirty metadata is written back for an fs with errors
[BUG]
During development of a minor feature (make sure all btrfs_bio::end_io()
is called in task context), I noticed a crash in generic/388, where
metadata writes triggered new works after btrfs_stop_all_workers().
It turns out that it can even happen without any code modification, just
using RAID5 for metadata and the same workload from generic/388 is going
to trigger the use-after-free.
[CAUSE]
If btrfs hits an error, the fs is marked as error, no new
transaction is allowed thus metadata is in a frozen state.
But there are some metadata modifications before that error, and they are
still in the btree inode page cache.
Since there will be no real transaction commit, all those dirty folios
are just kept as is in the page cache, and they can not be invalidated
by invalidate_inode_pages2() call inside close_ctree(), because they are
dirty.
And finally after btrfs_stop_all_workers(), we call iput() on btree
inode, which triggers writeback of those dirty metadata.
And if the fs is using RAID56 metadata, this will trigger RMW and queue
new works into rmw_workers, which is already stopped, causing warning
from queue_work() and use-after-free.
[FIX]
Add a special handling for write_one_eb(), that if the fs is already in
an error state, immediately mark the bbio as failure, instead of really
submitting them.
Then during close_ctree(), iput() will just discard all those dirty
tree blocks without really writing them back, thus no more new jobs for
already stopped-and-freed workqueues.
The extra discard in write_one_eb() also acts as an extra safenet.
E.g. the transaction abort is triggered by some extent/free space
tree corruptions, and since extent/free space tree is already corrupted
some tree blocks may be allocated where they shouldn't be (overwriting
existing tree blocks). In that case writing them back will further
corrupting the fs.
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (7.8): severity, escalated by confirmed exploitation. This CVE's 7.8 is its impact severity (EG Severity), not escalated.
- EG Severity
- 7.8 HIGHCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
- EG Likelihood
- 0.1% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-11-02). 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 low or medium mission impact; Track* at high (mission-essential systems).CISA BOD 26-04: 14 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 low or medium mission impact; Track* at high (mission-essential systems).
A fix is available. Apply it within your standard update timelines.
Exploitation none (no CISA value, KEV listing or exploit code on record) · Automatable no (CISA's BOD 26-04 default) · Technical impact total (CISA's BOD 26-04 default). EchelonGraph holds no SSVC assessment of this CVE from CISA: none of these inputs is from 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)14 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's BOD 26-04 default) · Technical impact total (CISA's BOD 26-04 default). Where an input reads “CISA's BOD 26-04 default”, no one has published it for this CVE, and CISA's implementation guidance says: “If “Automatable” and “Technical Impact” information items about a CVE ID are not available and the CVE ID is not in the KEV Catalog, CISA will treat its values as “no” and “total,” respectively, until CISA or a third party provides metadata about the CVE ID. CISA will always provide the Vulnrichment data for a CVE ID listed in the KEV Catalog.” 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