In the Linux kernel, the following vulnerability has been resolved:
af_unix: Unlink scc_entry in unix_del_edge().
Kyle Zeng reported that GC could free a dead SCC partially.
The scenario is as follows:
1) Create two SCCs:
X -. A <-> B
^--'
2) Run the following concurrently:
2-1) send() sk-B to sk-B from sk-X
2-2) close() both A and B
At 2-1), there is a small window where unix_add_edges()
publishes a new edge (B <-> B) to GC but its skb is not queued
by skb_queue_tail().
If 2-2) completes before skb_queue_tail() and GC is triggered,
it judges A <-> B as dead, but B is not freed because GC cannot
collect the not-yet-queued skb holding the B <-> B edge.
X -. A <-> B -. This edge is visible
^--' ^..' but skb is not
This itself is not a problem since the next GC run will judge
B as dead as well and free it finally.
X -. A <.> B -.
^--' ^--'
However, X's SCC forces the next GC to call unix_walk_scc_fast(),
and it iterates over A through B's scc_entry.
Let's unlink scc_entry before freeing the vertex in unix_del_edge().
SSVC (CISA's decision table, applied by EchelonGraph)Track at low, Track* at medium and Attend at high mission impact.
A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.
Exploitation public PoC (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