In the Linux kernel, the following vulnerability has been resolved:
phonet/pep: disable BH around forwarded sk_receive_skb()
The networking receive path is usually run from softirq context, but
protocols that take the socket lock may have packets stored in the
backlog and processed later from process context. In that case
release_sock() -> __release_sock() drops the slock with spin_unlock_bh()
and then calls sk->sk_backlog_rcv() with bottom halves enabled.
Typical sk_backlog_rcv handlers process the socket whose backlog is
being drained, so the BH state at entry is irrelevant for the slocks
they touch. pep_do_rcv() is different: when the inbound skb targets an
existing PEP pipe, it forwards the skb to a different *child* socket
via sk_receive_skb(). That helper takes the child slock with
bh_lock_sock_nested(), which is just spin_lock_nested() and assumes BH
is already off. The same child slock therefore ends up acquired with
BH on (process path) and with BH off (softirq path):
process context softirq context
--------------- ---------------
release_sock(listener) __netif_receive_skb()
__release_sock() phonet_rcv()
spin_unlock_bh() __sk_receive_skb(listener)
[BH now ENABLED] [BH already disabled]
sk_backlog_rcv: sk_backlog_rcv:
pep_do_rcv() pep_do_rcv()
sk_receive_skb(child) sk_receive_skb(child)
bh_lock_sock_nested(child) bh_lock_sock_nested(child)
=> SOFTIRQ-ON-W => IN-SOFTIRQ-W
Lockdep flags this as inconsistent lock state, and it can become a real
self-deadlock if a softirq on the same CPU tries to receive to the same
child socket while its slock is held in the BH-enabled path:
WARNING: inconsistent lock state
inconsistent {SOFTIRQ-ON-W} -> {IN-SOFTIRQ-W} usage.
(slock-AF_PHONET/1){+.?.}-{3:3}, at: __sk_receive_skb+0x1cf/0x900
__sk_receive_skb net/core/sock.c:563
sk_receive_skb include/net/sock.h:2022 [inline]
pep_do_rcv net/phonet/pep.c:675
sk_backlog_rcv include/net/sock.h:1190
__release_sock net/core/sock.c:3216
release_sock net/core/sock.c:3815
pep_sock_accept net/phonet/pep.c:879
Wrap the forwarded sk_receive_skb() in local_bh_disable() /
local_bh_enable() so the child slock is always acquired with BH off.
local_bh_disable() nests safely on the softirq path.
Discovered via in-house syzkaller fuzzing; the same root cause also
on the linux-6.1.y syzbot dashboard as extid 44f0626dd6284f02663c.
Reproduced under KASAN + LOCKDEP + PROVE_LOCKING, reproducer:
https://pastebin.com/A3t8xzCR
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
- 0.1% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-24). 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