In the Linux kernel, the following vulnerability has been resolved:
ptp: remove ptp->n_vclocks check logic in ptp_vclock_in_use()
There is no disagreement that we should check both ptp->is_virtual_clock
and ptp->n_vclocks to check if the ptp virtual clock is in use.
However, when we acquire ptp->n_vclocks_mux to read ptp->n_vclocks in
ptp_vclock_in_use(), we observe a recursive lock in the call trace
starting from n_vclocks_store().
============================================
WARNING: possible recursive locking detected
6.15.0-rc6 #1 Not tainted
--------------------------------------------
syz.0.1540/13807 is trying to acquire lock:
ffff888035a24868 (&ptp->n_vclocks_mux){+.+.}-{4:4}, at:
ptp_vclock_in_use drivers/ptp/ptp_private.h:103 [inline]
ffff888035a24868 (&ptp->n_vclocks_mux){+.+.}-{4:4}, at:
ptp_clock_unregister+0x21/0x250 drivers/ptp/ptp_clock.c:415
but task is already holding lock:
ffff888030704868 (&ptp->n_vclocks_mux){+.+.}-{4:4}, at:
n_vclocks_store+0xf1/0x6d0 drivers/ptp/ptp_sysfs.c:215
other info that might help us debug this:
Possible unsafe locking scenario:
CPU0
----
lock(&ptp->n_vclocks_mux);
lock(&ptp->n_vclocks_mux);
* DEADLOCK *
....
============================================
The best way to solve this is to remove the logic that checks
ptp->n_vclocks in ptp_vclock_in_use().
The reason why this is appropriate is that any path that uses
ptp->n_vclocks must unconditionally check if ptp->n_vclocks is greater
than 0 before unregistering vclocks, and all functions are already
written this way. And in the function that uses ptp->n_vclocks, we
already get ptp->n_vclocks_mux before unregistering vclocks.
Therefore, we need to remove the redundant check for ptp->n_vclocks in
ptp_vclock_in_use() to prevent recursive locking.
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 2026-10-23). 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: 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.
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