EchelonGraph verdictMonitorRemediate within your standard update timelines (the SSVC decision on this page).
- •Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0.2%CVSS: 4.8Exploit: None knownExposed services: Not assessed
A fix is referenced (a reference tagged "Patch", often a source commit), but no release containing it is confirmed — find the release that contains it; until it is applied, mitigate (WAF / firewall / segmentation).
The RFC 6528 initial-sequence-number implementation in subsys/net/ip/tcp.c derived every TCP ISN from SHA-256(unique_key || four-tuple) plus a uptime-derived offset, where unique_key is a 128-bit secret filled once by sys_csrand_get(). The return value of that call was discarded and the once guard was latched to true even when the call failed. Because sys_csrand_get() leaves the destination buffer untouched on failure (it deliberately propagates the entropy-driver error rather than filling the buffer), a single failed call left unique_key as its all-zero BSS content for the remainder of the boot, with no retry, no log message and no fallback.
A failure of the cryptographic random source is required to reach the weak state — for example -ENODEV/-EIO from the entropy driver in subsys/random/random_entropy_device.c (the in-tree comment notes that the hardware RNG "might still be gathering entropy during early boot situations"), or psa_generate_random() failing in subsys/random/random_psa.c when PSA crypto is not initialised or is backed by a Bluetooth-HCI entropy device that is not yet up. The first TCP connection is what triggers key generation, so a remote peer that reaches a listening port immediately after boot, or that can provoke a reboot, has indirect influence over whether generation coincides with that window. tcp_init_isn() is called for every passive open in tcp_conn_new() and every active open in net_tcp_connect(), so the poisoned key governs all TCP connections for that boot.
With an all-zero key the ISN becomes a public function of the connection four-tuple plus a device-wide time offset. An off-path attacker can compute the hash term offline for any four-tuple and recover the shared time offset from a single observed ISN, after which the ISN the device will pick for other four-tuples is predictable. That defeats exactly the protection RFC 6528 provides: blind TCP connection spoofing against peers that trust the source address, and blind data injection into or reset of connections whose four-tuple can be guessed. Devices whose entropy source never errors were never in the weak state.
The fix moves key generation into a single guarded helper that latches only on success, logs the error otherwise, and makes tcp_init_isn() fall back to sys_rand32_get() — the behaviour already used when CONFIG_NET_TCP_ISN_RFC6528 is disabled — instead of hashing with a known-constant key.
SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Track* at high (mission-essential systems).
A fix is referenced, but no release containing it is confirmed. Check the referenced fix and the vendor's advisory for a release that contains it and apply that within your standard update timelines; until then, restrict network exposure of the affected system or apply the vendor's mitigation.
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