{"answers":{"affected":"","exploited":"There is no known exploitation of CVE-2026-18747 in the wild and no public exploit code.","fix":"No fix has been published for CVE-2026-18747 yet. Limit exposure of the affected software until one is available.","what":"CVE-2026-18747 is a medium-severity vulnerability in zephyrproject zephyr, published on 28 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim."},"fix_prompt":"Check this codebase for CVE-2026-18747 and fix it if it is affected.\n\nWhat it is: CVE-2026-18747 is a medium-severity vulnerability in zephyrproject zephyr, published on 28 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.\nExploitation: There is no known exploitation of CVE-2026-18747 in the wild and no public exploit code.\n\nAffected product: zephyrproject zephyr. No package-level version data is available, so check the vendor advisory linked from the reference page.\n\nTask:\n1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.\n2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.\n3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.\n4. Run the tests and summarise what changed and why.\n5. If nothing in the project is affected, say so and change nothing.\n\nReference: https://insights.sbomify.com/CVE-2026-18747/ (Markdown: https://insights.sbomify.com/CVE-2026-18747/index.md)","id":"CVE-2026-18747","markdown":"https://insights.sbomify.com/CVE-2026-18747/index.md","name":"CVE-2026-18747","record":{"aliases":["GHSA-g6cx-xj75-hvfw"],"analysis":{"component_type":"operating_system","fix_type":"patch","impacts":["data_read","denial_of_service"],"network_reachable":"adjacent_or_local","non_default_config":false,"product_category":"Zephyr RTOS","requires_auth":"none","summary":"An integer underflow in Zephyr's MCUmgr serial transport allows unauthenticated attackers to trigger out-of-bounds reads via a crafted console message.","user_interaction":"not_required","vuln_class":"integer_overflow"},"analysis_generated_by":"qwen3.8-flash-next","assigner":"zephyr","cpe":[],"cvss":{"score":6.8,"severity":"medium","source":"cna","vector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H","version":"3.1"},"cwes":[{"id":"CWE-191","name":"Integer Underflow (Wrap or Wraparound)"},{"id":"CWE-125","name":"Out-of-bounds Read"}],"description":"The MCUmgr SMP-over-console transport decodes a base64 frame, reads a 16-bit packet length from it, verifies a CRC and then unconditionally strips the trailing CRC with rx_ctxt-\u003enb-\u003elen -= 2U; in mcumgr_serial_process_frag() (subsys/mgmt/mcumgr/transport/src/serial_util.c). mcumgr_serial_extract_len() accepted any declared length, including 0 and 1, and a packet declaring length 0 passes the checksum test for free because crc16_itu_t() over zero bytes returns the zero seed. Since net_buf::len is a uint16_t, the subtraction underflows and the buffer is handed to SMP claiming roughly 65 KB of payload while its data area is only CONFIG_MCUMGR_TRANSPORT_NETBUF_SIZE bytes (default 384).\n\nThe trigger is a single unauthenticated 7-byte line on the management console — the 0x06 0x09 packet marker followed by the base64 group AAA= and a newline — delivered to any transport built on this helper: CONFIG_MCUMGR_TRANSPORT_UART (smp_uart.c) or CONFIG_MCUMGR_TRANSPORT_SHELL (smp_shell.c), both of which select MCUMGR_TRANSPORT_SERIAL_HAS_SMP_OVER_CONSOLE. No prior session state, fragmentation or credentials are required to trigger the underflow, and the malformed frame is mishandled before any command handler or command-level access control runs. The attacker only needs write access to that console, which on many boards is a USB CDC-ACM port rather than a bare UART header.\n\nWith the inflated length, smp_process_request_packet() in subsys/mgmt/mcumgr/smp/src/smp.c loses its bound: cbor_nb_reader_init() gives the CBOR decoder a ~65 KB window into a 384-byte buffer, and each request header's nh_len is checked only against the inflated length. On its own the 7-byte frame re-parses whatever stale bytes the reused pool buffer still holds, typically a replay of the previously received request followed by a parse error, without leaving the buffer. Because the transport is unauthenticated, though, the attacker also controls the frames sent before the trigger, and can stage buffer contents so that a request succeeds with an nh_len larger than the buffer; net_buf_pull(), guarded only by __ASSERT_NO_MSG, then moves the parse cursor out of bounds and the loop reads further headers and CBOR from adjacent memory. The consequence is an out-of-bounds read that can fault the MCUmgr thread (denial of service); memory disclosure is also possible, since the default-enabled os echo handler (CONFIG_MCUMGR_GRP_OS_ECHO) decodes its string inside that window and copies it into its response. There is no integrity gain beyond what the unauthenticated transport already permits.\n\nThe fix rejects any declared packet length of two bytes or fewer in mcumgr_serial_extract_len(), so the CRC-strip subtraction can no longer underflow. The identical pattern remains in the test-only loopback transport subsys/mgmt/mcumgr/transport/src/smp_dummy.c (CONFIG_MCUMGR_TRANSPORT_DUMMY), which has no external input path and therefore carries no practical exposure.","ecosystems":[],"exploits":{"exploitdb":0,"first_seen":null,"github_poc":0,"max_poc_stars":null,"metasploit":0,"nuclei":0,"refs":[],"tier":"none_known"},"has_fix":false,"headline":"Integer underflow of net_buf length in the MCUmgr serial (SMP over console) transport leads to out-of-bounds read","id":"CVE-2026-18747","indexable":true,"kev":null,"kind":"cve","links":{"ecosystem":null,"product":null,"products":[],"type":"integer_overflow","year":"2026"},"n_packages":0,"n_references":2,"next":{"headline":"Out-of-bounds read in Bluetooth Classic A2DP codec information element handling","id":"CVE-2026-18748"},"packages":[],"prev":{"headline":"NULL pointer dereference in Zephyr LwM2M client when the CoAP Block1 context pool is exhausted","id":"CVE-2026-18746"},"products":["zephyr"],"published":"2026-09-28","related":[],"sources":[{"class":"attribution","licence":"CVE Terms of Use (MITRE)","name":"CVE List","prefix":"CVE"},{"class":"attribution","licence":"CWE Terms of Use","name":"CWE (MITRE)"},{"class":"attribution","licence":"FIRST CVSS licence","name":"CVSS (FIRST)"}],"ssvc":{"automatable":"no","exploitation":"none","technical_impact":"partial"},"state":"PUBLISHED","updated":"2026-09-30","vendors":["zephyrproject"]},"summary":"An integer underflow in Zephyr's MCUmgr serial transport allows unauthenticated attackers to trigger out-of-bounds reads via a crafted console message.","url":"https://insights.sbomify.com/CVE-2026-18747/"}