CVE-2026-15890: zephyr Race Condition (CVSS 5.3)

Description

The default AEAD nonce provider for the PSA Internal Trusted Storage transform module, secure_storage_its_transform_aead_get_nonce() in subsys/secure_storage/src/its/transform/aead_get.c, stores its nonce counter in unsynchronized function-local static variables (s_nonce and s_nonce_initialized). Every ITS write obtains its AES-GCM or ChaCha20-Poly1305 nonce here via secure_storage_its_transform_to_store(). Because the function held no lock, two threads calling it concurrently race on the shared statics: the initialization path (psa_generate_random() followed by memcpy()) and the non-atomic increment-then-copy path can each hand the same nonce value to two distinct encryption operations, and can lose increments so the counter repeats values it was designed never to repeat. The ITS layer (secure_storage_its_set() in subsys/secure_storage/src/its/implementation.c) performs no serialization of its own, so concurrent same-UID writes reach the racy provider directly. Reusing a nonce with the same key under AES-GCM or ChaCha20-Poly1305 is a catastrophic AEAD failure: it leaks the XOR of the two plaintexts (ITS routinely stores secrets, including PSA persistent keys) and, for GCM, exposes the authentication key, enabling forgery of stored entries. Because the AEAD key is derived per entry UID, the security-relevant collision is two concurrent writes to the same UID both receiving the same nonce; an adversary able to read the raw backing storage can then exploit the reuse. Both ITS store back-ends shipped with Zephyr, zms.c and the settings/NVS back-end in settings.c, are log-structured flash stores with deferred garbage collection, so an entry superseded by a rewrite remains physically present in the partition until its sector is reclaimed. Two same-UID writes that race therefore leave both ciphertexts readable in the raw image at once, which is the condition the nonce reuse needs to be exploitable. The trigger remains narrow: both built-in key providers (DEVICE_ID_HASH and ENTRY_UID_HASH) salt the derived key with the entry UID, so reuse across different UIDs is harmless, and the exposure requires an application that writes the same UID concurrently from two threads. The fix serializes the provider with a K_MUTEX_DEFINE(s_nonce_mutex) held for the duration of nonce generation.

Metrics

CVSS 3.1

5.3/10

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:N

EPSS Probability

0.06%

0.0th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
zephyrproject	zephyr	>= 4.0.0, < 4.3.2; >= 4.4.0, < 4.4.2

References

Timeline

Published: Sep 21, 2026
Last Modified: Sep 22, 2026
Status: Received

Frequently Asked Questions

What is CVE-2026-15890?

The default AEAD nonce provider for the PSA Internal Trusted Storage transform module, secure_storage_its_transform_aead_get_nonce() in subsys/secure_storage/src/its/transform/aead_get.c, stores its nonce counter in unsynchronized function-local static variables (s_nonce and s_nonce_initialized). Every ITS write obtains its AES-GCM or ChaCha20-Poly1305 nonce here via secure_storage_its_transform_to_store(). Because the function held no lock, two threads calling it concurrently race on the shared statics: the initialization path (psa_generate_random() followed by memcpy()) and the non-atomic increment-then-copy path can each hand the same nonce value to two distinct encryption operations, and can lose increments so the counter repeats values it was designed never to repeat. The ITS layer (secure_storage_its_set() in subsys/secure_storage/src/its/implementation.c) performs no serialization of its own, so concurrent same-UID writes reach the racy provider directly. Reusing a nonce with the same key under AES-GCM or ChaCha20-Poly1305 is a catastrophic AEAD failure: it leaks the XOR of the two plaintexts (ITS routinely stores secrets, including PSA persistent keys) and, for GCM, exposes the authentication key, enabling forgery of stored entries. Because the AEAD key is derived per entry UID, the security-relevant collision is two concurrent writes to the same UID both receiving the same nonce; an adversary able to read the raw backing storage can then exploit the reuse. Both ITS store back-ends shipped with Zephyr, zms.c and the settings/NVS back-end in settings.c, are log-structured flash stores with deferred garbage collection, so an entry superseded by a rewrite remains physically present in the partition until its sector is reclaimed. Two same-UID writes that race therefore leave both ciphertexts readable in the raw image at once, which is the condition the nonce reuse needs to be exploitable. The trigger remains narrow: both built-in key providers (DEVICE_ID_HASH and ENTRY_UID_HASH) salt the derived key with the entry UID, so reuse across different UIDs is harmless, and the exposure requires an application that writes the same UID concurrently from two threads. The fix serializes the provider with a K_MUTEX_DEFINE(s_nonce_mutex) held for the duration of nonce generation.

How severe is CVE-2026-15890?

CVE-2026-15890 has a CVSS score of 5.3/10 (MEDIUM severity). The EPSS model estimates a 0.06% probability of exploitation in the next 30 days.

How do I fix CVE-2026-15890?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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