CVE-2026-19736 : Detail

CVE-2026-19736

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2026-10-11
18h16 +00:00
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2026-11-04
05h18 +00:00
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Deskripsi CVE

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.

Informasi CVE

Kelemahan Terkait

CWE-ID Nama Kelemahan Sumber
CWE-787 Out-of-bounds Write
The product writes data past the end, or before the beginning, of the intended buffer.

Metrik

Metrik Skor Tingkat keparahan CVSS Vektor Sumber
V3.1 7.8 HIGH CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Base: Exploitabilty Metrics

The Exploitability metrics reflect the characteristics of the thing that is vulnerable, which we refer to formally as the vulnerable component.

Attack Vector

This metric reflects the context by which vulnerability exploitation is possible.

Local

The vulnerable component is not bound to the network stack and the attacker’s path is via read/write/execute capabilities.

Attack Complexity

This metric describes the conditions beyond the attacker’s control that must exist in order to exploit the vulnerability.

Low

Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success when attacking the vulnerable component.

Privileges Required

This metric describes the level of privileges an attacker must possess before successfully exploiting the vulnerability.

Low

The attacker requires privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges has the ability to access only non-sensitive resources.

User Interaction

This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable component.

None

The vulnerable system can be exploited without interaction from any user.

Base: Scope Metrics

The Scope metric captures whether a vulnerability in one vulnerable component impacts resources in components beyond its security scope.

Scope

Formally, a security authority is a mechanism (e.g., an application, an operating system, firmware, a sandbox environment) that defines and enforces access control in terms of how certain subjects/actors (e.g., human users, processes) can access certain restricted objects/resources (e.g., files, CPU, memory) in a controlled manner. All the subjects and objects under the jurisdiction of a single security authority are considered to be under one security scope. If a vulnerability in a vulnerable component can affect a component which is in a different security scope than the vulnerable component, a Scope change occurs. Intuitively, whenever the impact of a vulnerability breaches a security/trust boundary and impacts components outside the security scope in which vulnerable component resides, a Scope change occurs.

Unchanged

An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.

Base: Impact Metrics

The Impact metrics capture the effects of a successfully exploited vulnerability on the component that suffers the worst outcome that is most directly and predictably associated with the attack. Analysts should constrain impacts to a reasonable, final outcome which they are confident an attacker is able to achieve.

Confidentiality Impact

This metric measures the impact to the confidentiality of the information resources managed by a software component due to a successfully exploited vulnerability.

High

There is a total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server.

Integrity Impact

This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information.

High

There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.

Availability Impact

This metric measures the impact to the availability of the impacted component resulting from a successfully exploited vulnerability.

High

There is a total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Temporal Metrics

The Temporal metrics measure the current state of exploit techniques or code availability, the existence of any patches or workarounds, or the confidence in the description of a vulnerability.

Environmental Metrics

These metrics enable the analyst to customize the CVSS score depending on the importance of the affected IT asset to a user’s organization, measured in terms of Confidentiality, Integrity, and Availability.

vulnerabilities@zephyrproject.org

Referensi