In the Linux kernel, the following vulnerability has been resolved:
cxl/port: Fix use after free of parent_port in cxl_detach_ep()
cxl_detach_ep() is called during bottom-up removal when all CXL memory
devices beneath a switch port have been removed. For each port in the
hierarchy it locks both the port and its parent, removes the endpoint,
and if the port is now empty, marks it dead and unregisters the port
by calling delete_switch_port(). There are two places during this work
where the parent_port may be used after freeing:
First, a concurrent detach may have already processed a port by the
time a second worker finds it via bus_find_device(). Without pinning
parent_port, it may already be freed when we discover port->dead and
attempt to unlock the parent_port. In a production kernel that's a
silent memory corruption, with lock debug, it looks like this:
[]DEBUG_LOCKS_WARN_ON(__owner_task(owner) != get_current())
[]WARNING: kernel/locking/mutex.c:949 at __mutex_unlock_slowpath+0x1ee/0x310
[]Call Trace:
[]mutex_unlock+0xd/0x20
[]cxl_detach_ep+0x180/0x400 [cxl_core]
[]devm_action_release+0x10/0x20
[]devres_release_all+0xa8/0xe0
[]device_unbind_cleanup+0xd/0xa0
[]really_probe+0x1a6/0x3e0
Second, delete_switch_port() releases three devm actions registered
against parent_port. The last of those is unregister_port() and it
calls device_unregister() on the child port, which can cascade. If
parent_port is now also empty the device core may unregister and free
it too. So by the time delete_switch_port() returns, parent_port may
be free, and the subsequent device_unlock(&parent_port->dev) operates
on freed memory. The kernel log looks same as above, with a different
offset in cxl_detach_ep().
Both of these issues stem from the absence of a lifetime guarantee
between a child port and its parent port.
Establish a lifetime rule for ports: child ports hold a reference to
their parent device until release. Take the reference when the port
is allocated and drop it when released. This ensures the parent is
valid for the full lifetime of the child and eliminates the use after
free window in cxl_detach_ep().
This is easily reproduced with a reload of cxl_acpi in QEMU with CXL
devices present.
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
- 0.2% within 30 daysSource: FIRST EPSS. 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