In the Linux kernel, the following vulnerability has been resolved:
null_blk: fix poll request timeout handling
When doing io_uring benchmark on /dev/nullb0, it's easy to crash the
kernel if poll requests timeout triggered, as reported by David. [1]
BUG: kernel NULL pointer dereference, address: 0000000000000008
Workqueue: kblockd blk_mq_timeout_work
RIP: 0010:null_timeout_rq+0x4e/0x91
Call Trace:
? null_timeout_rq+0x4e/0x91
blk_mq_handle_expired+0x31/0x4b
bt_iter+0x68/0x84
? bt_tags_iter+0x81/0x81
__sbitmap_for_each_set.constprop.0+0xb0/0xf2
? __blk_mq_complete_request_remote+0xf/0xf
bt_for_each+0x46/0x64
? __blk_mq_complete_request_remote+0xf/0xf
? percpu_ref_get_many+0xc/0x2a
blk_mq_queue_tag_busy_iter+0x14d/0x18e
blk_mq_timeout_work+0x95/0x127
process_one_work+0x185/0x263
worker_thread+0x1b5/0x227
This is indeed a race problem between null_timeout_rq() and null_poll().
null_poll() null_timeout_rq()
spin_lock(&nq->poll_lock)
list_splice_init(&nq->poll_list, &list)
spin_unlock(&nq->poll_lock)
while (!list_empty(&list))
req = list_first_entry()
list_del_init()
...
blk_mq_add_to_batch()
// req->rq_next = NULL
spin_lock(&nq->poll_lock)
// rq->queuelist->next == NULL
list_del_init(&rq->queuelist)
spin_unlock(&nq->poll_lock)
Fix these problems by setting requests state to MQ_RQ_COMPLETE under
nq->poll_lock protection, in which null_timeout_rq() can safely detect
this race and early return.
Note this patch just fix the kernel panic when request timeout happen.
[1] https://lore.kernel.org/all/3893581.1691785261@warthog.procyon.org.uk/
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 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