CVE-2026-19742
LowCVSS 3.7Exploitation Probability (EPSS)
Low risk16th percentile - higher than 16% of all known CVEs
Summary
The vulnerability affects the IPv6 stack in Zephyr RTOS, where the key used to generate stable (RFC 7217) and temporary (RFC 8981) interface identifiers was derived using sys_rand_get(), which is not cryptographically secure. As a result, an observer of network traffic can recover the generator state and reconstruct the key, allowing prediction of the device's IPv6 addresses and tracking across networks.
Risk Assessment
An attacker can predict the device's IPv6 addresses within a /64 without scanning and track the device across networks and prefixes, defeating the privacy properties these features are meant to provide. There is no memory-safety, integrity, or availability impact.
Recommendation
Update Zephyr RTOS to a version containing the fix that generates the key with sys_csrand_get() and aborts IID generation with -EIO when cryptographic randomness is unavailable. If CONFIG_NET_IPV6_IID_STABLE or CONFIG_NET_IPV6_PE are not used, they remain disabled by default.
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Original NVD description (English source)
The IPv6 stack derived the long-lived secret key used to compute RFC 7217 stable interface identifiers (gen_stable_iid() in subsys/net/ip/ipv6.c) and RFC 8981 temporary interface identifiers (gen_temporary_iid() in subsys/net/ip/ipv6_pe.c) with sys_rand_get(). That API is documented as not cryptographically secure, while both RFCs require this key to be an unpredictable random value of at least 128 bits — the unpredictability of every generated IID rests entirely on it. Depending on the platform, sys_rand_get() resolves either to a hardware entropy device or, on boards whose entropy driver sets CONFIG_ENTROPY_NEEDS_PRNG, to the non-cryptographic xoshiro128++ generator in subsys/random/random_xoshiro128.c, which keeps a single global 128-bit state shared with every other sys_rand_get() consumer. Many of those consumers put their output directly on the wire (ephemeral source ports, DNS query IDs, CoAP message IDs and tokens, DHCPv6 transaction IDs, WebSocket masking keys), and the xoshiro state transition is invertible, so an observer of a device's traffic can recover the generator state and reconstruct the IID secret key. Additionally, with the entropy-device backend sys_rand_get() silently falls back to k_cycle_get_32() samples when the entropy driver fails, and returns no error, so the key could be derived from the cycle counter without the caller noticing. With the key known, stable IIDs become directly computable for any prefix (the remaining HMAC inputs — prefix, interface index, interface name, DAD counter — are guessable), and temporary IIDs become linkable after a cheap search over the mixed-in k_uptime_get_32() value. This defeats the properties both features exist to provide: an attacker can track a device across networks and prefixes, and can predict its address inside a /64 without scanning, removing the usual barrier to directly targeting the host. There is no memory-safety, integrity, or availability impact. The fix generates the key with sys_csrand_get() and aborts IID generation with -EIO when no cryptographic randomness is available, instead of silently deriving addresses from a predictable key. Both CONFIG_NET_IPV6_IID_STABLE and CONFIG_NET_IPV6_PE are experimental and disabled by default; builds using CONFIG_TEST_RANDOM_GENERATOR remain predictable by design, as sys_csrand_get() is deliberately routed back to the test generator there.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS