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CVE-2026-19736

Status: Awaiting AnalysisHigh (7.8)—
Severity7.8High · CVSS 3.1
Exploitation probability0.11 %higher than 1% of CVEs
Active exploitationNonot in the CISA catalog
Public exploitNot knownno public code found

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.

Read full descriptionShow less

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.

CVSS

Base score
7.8
Version
3.1
Vector
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Exploitation probability (EPSS)

Probability of exploitation in the next 30 days
0.11 %
Percentile among all scored CVEs
1
Score date
10/21/2026

EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).

ATT&CK techniques

How this vulnerability is exploited and what the attacker gains, in MITRE ATT&CK terms.

Buffer overflow (CWE-787) con acceso local y sin interacción del usuario. Permite corrupción de memoria del kernel (~127 bytes) y ejecución de código o escalada de privilegios mediante sobrescritura de estructuras críticas.

Inferred by our analysis agent from the official description, CVSS vector and CWE, and checked by a supervisor. May contain errors.

ATT&CK mitigations that cover these techniques

Threat Intelligence ProgramRestrict File and Directory PermissionsRemote Data StorageExecution PreventionEncrypt Sensitive InformationApplication Isolation and Sandboxing

Affected technologies (1)

⚠ AI-inferred from the description — NVD hasn't analyzed this CVE yet, these aren't verified CPEs.

Zephyrproject — ZephyrAI

CWEs

References

Show 2 references

Raw JSON (NVD)

Show
{
  "id": "CVE-2026-19736",
  "cveTags": [],
  "metrics": {
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-19736",
          "role": "CISA Coordinator",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "total"
            }
          ],
          "version": "2.0.3",
          "timestamp": "2026-10-15T17:57:42.294702Z"
        }
      }
    ],
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "vulnerabilities@zephyrproject.org",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 7.8,
          "attackVector": "LOCAL",
          "baseSeverity": "HIGH",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
          "integrityImpact": "HIGH",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 5.9,
        "exploitabilityScore": 1.8
      }
    ]
  },
  "affected": [
    {
      "source": "vulnerabilities@zephyrproject.org",
      "affectedData": [
        {
          "vendor": "zephyrproject",
          "product": "zephyr",
          "versions": [
            {
              "status": "affected",
              "version": "4.3.0",
              "versionType": "semver",
              "lessThanOrEqual": "4.4.2"
            }
          ],
          "packageName": "zephyr",
          "programFiles": [
            "drivers/entropy/entropy_mcux_trng.c"
          ],
          "collectionURL": "https://github.com/zephyrproject-rtos/zephyr",
          "defaultStatus": "unaffected",
          "programRoutines": [
            {
              "name": "entropy_get_entropy"
            },
            {
              "name": "entropy_mcux_trng_get_entropy"
            }
          ]
        }
      ]
    }
  ],
  "published": "2026-10-11T18:16:58.810",
  "references": [
    {
      "url": "https://github.com/zephyrproject-rtos/zephyr/commit/2c132efaf03a5d45aeaf7b0531c1107db7a36a3d",
      "source": "vulnerabilities@zephyrproject.org"
    },
    {
      "url": "https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-3f6q-3949-rqph",
      "source": "vulnerabilities@zephyrproject.org"
    }
  ],
  "vulnStatus": "Awaiting Analysis",
  "weaknesses": [
    {
      "type": "Secondary",
      "source": "vulnerabilities@zephyrproject.org",
      "description": [
        {
          "lang": "en",
          "value": "CWE-787"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "lang": "en",
      "value": "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.\n\nentropy_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().\n\nImpact 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.\n\nThe 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."
    }
  ],
  "lastModified": "2026-10-15T19:17:37.463",
  "sourceIdentifier": "vulnerabilities@zephyrproject.org"
}