{"dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": {"cveId": "CVE-2026-12631", "assignerOrgId": "e2e69745-5e70-4e92-8431-deb5529a81ad", "state": "PUBLISHED", "assignerShortName": "zephyr", "dateReserved": "2026-06-18T15:22:26.927Z", "datePublished": "2026-08-18T20:55:42.859Z", "dateUpdated": "2026-08-18T20:55:42.859Z"}, "containers": {"cna": {"providerMetadata": {"orgId": "e2e69745-5e70-4e92-8431-deb5529a81ad", "shortName": "zephyr", "dateUpdated": "2026-08-18T20:55:42.859Z"}, "title": "Broken access-control denial in k_thread_join/k_thread_abort syscall validation in Zephyr kernel", "descriptions": [{"lang": "en", "value": "The Zephyr kernel validates the k_thread_join() and k_thread_abort() system calls (declared __syscall in include/zephyr/kernel.h) through thread_obj_validate() in kernel/thread.c. Its default switch branch is the access-denied path, taken when k_object_validate() returns -EPERM (the calling user thread was never granted access to the target thread object) or -EBADF (the supplied pointer is not a registered kernel object of the right type). That branch invoked K_OOPS(K_SYSCALL_VERIFY_MSG(ret, \"access denied\")), but K_SYSCALL_VERIFY_MSG treats a true expression as success; the non-zero error code ret therefore read as \"verified OK\", the kernel oops was never raised, and control fell through to CODE_UNREACHABLE.\n\nBecause k_thread_join() and k_thread_abort() are system calls, an unprivileged user-mode thread (under CONFIG_USERSPACE) can reach this denial path directly by calling either syscall on a thread object it does not own. Instead of the offending thread being cleanly terminated, execution reaches __builtin_unreachable() while running in supervisor mode inside the syscall handler.\n\nOn Clang builds CODE_UNREACHABLE emits an illegal-instruction trap, so a user thread can deterministically crash the kernel \u2014 a locally triggerable denial of service that escapes the userspace sandbox. On GCC builds the path is undefined behavior: the compiler may drop the return-value handling for thread_obj_validate(), so it can return an undefined bool; if that is false, the caller proceeds into the real k_thread_join()/k_thread_abort() implementation for a thread the user was never authorized to access, an access-control bypass.\n\nThe fix changes the verification expression to ret == 0, so a denied (non-zero) result now correctly raises K_OOPS and terminates the offending caller."}], "affected": [{"vendor": "zephyrproject", "product": "zephyr", "collectionURL": "https://github.com/zephyrproject-rtos/zephyr", "packageName": "zephyr", "defaultStatus": "unaffected", "programFiles": ["kernel/thread.c"], "versions": [{"version": "2.3.0", "status": "affected", "versionType": "semver", "lessThan": "4.4.2"}]}], "references": [{"url": "https://github.com/zephyrproject-rtos/zephyr/commit/bd1828652dfc217ba9f3a2221a7499cd8914ed9c", "name": "Fix commit", "tags": ["patch"]}, {"url": "https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-crfw-75jw-hjm3", "name": "GHSA-crfw-75jw-hjm3"}], "metrics": [{"format": "CVSS", "cvssV3_1": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H", "baseScore": 6.5, "baseSeverity": "MEDIUM"}}], "problemTypes": [{"descriptions": [{"lang": "en", "description": "auth", "cweId": "CWE-862", "type": "CWE"}]}], "x_generator": {"engine": "cvelib 1.8.0"}}}}

{}

{"affected": [{"affectedData": [{"collectionURL": "https://github.com/zephyrproject-rtos/zephyr", "defaultStatus": "unaffected", "packageName": "zephyr", "product": "zephyr", "programFiles": ["kernel/thread.c"], "vendor": "zephyrproject", "versions": [{"lessThan": "4.4.2", "status": "affected", "version": "2.3.0", "versionType": "semver"}]}], "source": "[email protected]"}], "cveTags": [], "descriptions": [{"lang": "en", "value": "The Zephyr kernel validates the k_thread_join() and k_thread_abort() system calls (declared __syscall in include/zephyr/kernel.h) through thread_obj_validate() in kernel/thread.c. Its default switch branch is the access-denied path, taken when k_object_validate() returns -EPERM (the calling user thread was never granted access to the target thread object) or -EBADF (the supplied pointer is not a registered kernel object of the right type). That branch invoked K_OOPS(K_SYSCALL_VERIFY_MSG(ret, \"access denied\")), but K_SYSCALL_VERIFY_MSG treats a true expression as success; the non-zero error code ret therefore read as \"verified OK\", the kernel oops was never raised, and control fell through to CODE_UNREACHABLE.\n\nBecause k_thread_join() and k_thread_abort() are system calls, an unprivileged user-mode thread (under CONFIG_USERSPACE) can reach this denial path directly by calling either syscall on a thread object it does not own. Instead of the offending thread being cleanly terminated, execution reaches __builtin_unreachable() while running in supervisor mode inside the syscall handler.\n\nOn Clang builds CODE_UNREACHABLE emits an illegal-instruction trap, so a user thread can deterministically crash the kernel \u2014 a locally triggerable denial of service that escapes the userspace sandbox. On GCC builds the path is undefined behavior: the compiler may drop the return-value handling for thread_obj_validate(), so it can return an undefined bool; if that is false, the caller proceeds into the real k_thread_join()/k_thread_abort() implementation for a thread the user was never authorized to access, an access-control bypass.\n\nThe fix changes the verification expression to ret == 0, so a denied (non-zero) result now correctly raises K_OOPS and terminates the offending caller."}], "id": "CVE-2026-12631", "lastModified": "2026-08-18T21:16:33.647", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "LOCAL", "availabilityImpact": "HIGH", "baseScore": 6.5, "baseSeverity": "MEDIUM", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "privilegesRequired": "LOW", "scope": "CHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H", "version": "3.1"}, "exploitabilityScore": 2.0, "impactScore": 4.0, "source": "[email protected]", "type": "Secondary"}]}, "published": "2026-08-18T21:16:33.647", "references": [{"source": "[email protected]", "url": "https://github.com/zephyrproject-rtos/zephyr/commit/bd1828652dfc217ba9f3a2221a7499cd8914ed9c"}, {"source": "[email protected]", "url": "https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-crfw-75jw-hjm3"}], "sourceIdentifier": "[email protected]", "vulnStatus": "Received", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-862"}], "source": "[email protected]", "type": "Secondary"}]}

{}

{"affected": [{"configurations": [{"platform": null, "status": "affected", "versions": {"scheme": "semver", "value": "[2.3.0,4.4.2)"}}], "enrichment": {"confidence": 100.0, "confidence_source": "matching", "scores": [{"score": 100.0, "source": "matching"}]}, "original": {"product": "zephyr", "source": "cna", "vendor": "zephyrproject"}, "product": "zephyr", "vendor": "zephyrproject"}], "created": "2026-08-18T23:00:13.467805+00:00", "updated": "2026-08-18T23:00:13.467824+00:00", "vendors": ["zephyrproject", "zephyrproject$PRODUCT$zephyr"]}