In the Linux kernel, the following vulnerability has been resolved:
mptcp: fix stale skb->sk reference on subflow close
The backlog list is updated by mptcp_data_ready() under
mptcp_data_lock(). The cleanup of backlog references to a closing
subflow, however, was performed in mptcp_close_ssk(), before
__mptcp_close_ssk() acquires the ssk lock, and while holding neither
the ssk lock nor mptcp_data_lock().
Because that traversal ran without mptcp_data_lock(), concurrent softirq
RX processing on another CPU (subflow_data_ready() -> mptcp_data_ready()
-> __mptcp_add_backlog(), under mptcp_data_lock()) could add a backlog
entry referencing the ssk while the cleanup loop was in progress. Such
an entry could be missed by the cleanup, or the concurrent list update
could corrupt the traversal, leaving skb->sk pointing at the ssk after
it is freed.
A later mptcp_backlog_purge() then dereferences the stale pointer,
triggering a warning in inet_sock_destruct() (ssk->sk_rmem_alloc != 0)
followed by a use-after-free in mptcp_backlog_purge().
Fix this by moving the backlog cleanup into __mptcp_close_ssk(), after
subflow->closing is set to 1 and while the ssk lock is still held,
serialized under mptcp_data_lock(). The cleanup runs only on the push
path (MPTCP_CF_PUSH), where backlog references accumulate; on other
teardown paths the caller already handles cleanup.
With subflow->closing set and mptcp_data_lock() held across the purge,
any concurrent mptcp_data_ready() either completes its enqueue before
the purge runs and is caught, or observes closing=1 and bails out. Once
mptcp_data_unlock() is reached, no new skb referencing the ssk can be
enqueued, so the cleanup is exhaustive.
Remove the unprotected traversal from mptcp_close_ssk() entirely.
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (9.8): severity, escalated by confirmed exploitation. This CVE's 9.8 is its impact severity (EG Severity), not escalated.
- EG Severity
- 9.8 CRITICALCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
- EG Likelihood
- 0.5% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-19). 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