Zephyr Project up to 4.4.2 NXP MCUX TRNG Entropy Driver entropy_mcux_trng.c entropy_get_entropy dataSize out-of-bounds write

Summaryinfo

A vulnerability was found in Zephyr Project Zephyr up to 4.4.2. It has been rated as very critical. Affected is the function entropy_get_entropy of the file drivers/entropy/entropy_mcux_trng.c of the component NXP MCUX TRNG Entropy Driver. Performing a manipulation of the argument dataSize results in out-of-bounds write. This vulnerability is known as CVE-2026-19736. Attacking locally is a requirement. No exploit is available. It is suggested to install a patch to address this issue.

Detailsinfo

A vulnerability classified as very critical has been found in Zephyr Project Zephyr up to 4.4.2. This affects the function entropy_get_entropy of the file drivers/entropy/entropy_mcux_trng.c of the component NXP MCUX TRNG Entropy Driver. The manipulation of the argument dataSize with an unknown input leads to a out-of-bounds write vulnerability. CWE is classifying the issue as CWE-787. The product writes data past the end, or before the beginning, of the intended buffer. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

The NXP MCUX TRNG entropy driver in drivers/entropy/entropy_mcux_trng.c passed the caller's byte count straight to the vendor SDK routine TRNG_GetRandomData(). On i.MX RT5xx and RT6xx parts the SDK compiles its TRNG_SW_HEALTH_TESTS variant, which always copies whole 32-bit words and draws entropy rounded up to a multiple of 128 bytes. Its "caller buffer is full" guard tests dataSize == 0, so a request whose length is not a multiple of four makes dataSize underflow past zero and the SDK keeps writing into the caller's buffer for the entire extraction: a 1-byte request results in 128 bytes written, and any non-word-multiple length overflows by up to 127 bytes. entropy_get_entropy() is a syscall, and its verifier in drivers/entropy/entropy_handlers.c validates only the requested length via K_SYSCALL_MEMORY_WRITE(). With CONFIG_USERSPACE enabled, an unprivileged user-mode thread that has merely been granted the entropy device can therefore choose both the destination address and a length such as 1, and cause the kernel to write up to 127 bytes beyond the region it proved it owns. On these Cortex-M33 targets there is no MMU, so user partitions and kernel data share one SRAM and the overflow can land in adjacent kernel state. The same defect is reached from kernel mode by any caller requesting a non-word-multiple length, including getentropy() and, in builds where sys_csrand_get()/sys_rand_get() resolve to the hardware generator, sys_rand8_get() and sys_rand16_get(). Impact is memory corruption of up to 127 bytes immediately following the supplied buffer — typically the caller's stack in kernel-mode use, or memory outside the caller's partition when driven through the syscall. The overflow offset is fully determined by the requested length and is therefore deterministic, while the written content is uncontrolled TRNG output; the practical consequences range from crashes and unpredictable state corruption to opportunistic escalation when kernel bookkeeping such as object permission bitmaps is overwritten. The affected devices are those where the MCUX SDK enables TRNG_SW_HEALTH_TESTS (MIMXRT595S, MIMXRT555S, MIMXRT533S, MIMXRT685S, MIMXRT633S), on which the TRNG is the zephyr,entropy chosen node; other SoCs using this driver take the SDK path that clamps the copy size and are unaffected. The fix routes any unaligned prefix and any sub-word tail through a local bounce word and hands the SDK only word-multiple sizes, so the SDK's word-granular writes can no longer pass the end of the caller's buffer.

The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2026-19736 since 08/13/2026. The exploitability is told to be easy. An attack has to be approached locally. Technical details are known, but no exploit is available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 10/11/2026).

Applying the patch 2c132efaf03a5d45aeaf7b0531c1107db7a36a3d is able to eliminate this problem.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Type

• Project Management Software

Vendor

• Zephyr Project

Name

• Zephyr

Version

• 4.4.0
• 4.4.1
• 4.4.2

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CPE 2.2info

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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