Zephyr Project up to 4.4.x IPv6 Stack subsys/net/ip/ipv6.c gen_stable_iid/gen_temporary_iid random values

Summaryinfo

A vulnerability has been found in Zephyr Project Zephyr up to 4.4.x and classified as problematic. This affects the function gen_stable_iid/gen_temporary_iid of the file subsys/net/ip/ipv6.c of the component IPv6 Stack. The manipulation leads to random values. This vulnerability is uniquely identified as CVE-2026-19742. The attack is possible to be carried out remotely. No exploit exists. The affected component should be upgraded.

Detailsinfo

A vulnerability was found in Zephyr Project Zephyr up to 4.4.x. It has been rated as problematic. This issue affects the function gen_stable_iid/gen_temporary_iid of the file subsys/net/ip/ipv6.c of the component IPv6 Stack. The manipulation with an unknown input leads to a random values vulnerability. Using CWE to declare the problem leads to CWE-330. The product uses insufficiently random numbers or values in a security context that depends on unpredictable numbers. Impacted is confidentiality. The summary by CVE is:

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.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-19742 since 08/13/2026. The exploitation is known to be difficult. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1600.001 according to MITRE ATT&CK.

Upgrading to version 4.5.0 eliminates this vulnerability.

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Productinfo

Type

• Project Management Software

Vendor

• Zephyr Project

Name

• Zephyr

Version

• 4.0
• 4.1
• 4.2
• 4.3
• 4.4

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CPE 2.2info

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