{"answers":{"affected":"","exploited":"There is no known exploitation of CVE-2026-18746 in the wild and no public exploit code.","fix":"No fix has been published for CVE-2026-18746 yet. Limit exposure of the affected software until one is available.","what":"CVE-2026-18746 is a medium-severity vulnerability in zephyrproject zephyr, published on 28 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim."},"fix_prompt":"Check this codebase for CVE-2026-18746 and fix it if it is affected.\n\nWhat it is: CVE-2026-18746 is a medium-severity vulnerability in zephyrproject zephyr, published on 28 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.\nExploitation: There is no known exploitation of CVE-2026-18746 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-2026-18746/ (Markdown: https://insights.sbomify.com/CVE-2026-18746/index.md)","id":"CVE-2026-18746","markdown":"https://insights.sbomify.com/CVE-2026-18746/index.md","name":"CVE-2026-18746","record":{"aliases":["GHSA-4q9g-2mhh-m7w7"],"analysis":{"component_type":"operating_system","fix_type":"patch","impacts":["denial_of_service"],"network_reachable":"yes","non_default_config":false,"product_category":"Zephyr RTOS","requires_auth":"none","summary":"An attacker can crash a Zephyr LwM2M client by exhausting the CoAP Block1 context pool, causing a null pointer dereference and device reset.","user_interaction":"not_required","vuln_class":"null_dereference"},"analysis_generated_by":"qwen3.8-flash-next","assigner":"zephyr","cpe":[],"cvss":{"score":5.9,"severity":"medium","source":"cna","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H","version":"3.1"},"cwes":[{"id":"CWE-476","name":"NULL Pointer Dereference"}],"description":"parse_write_op() in subsys/net/lib/lwm2m/lwm2m_message_handling.c handles inbound CoAP WRITE/CREATE requests that carry a Block1 option. For the first block of a transfer it called init_block_ctx() and then immediately stored the peer-selected block size with block_ctx-\u003ectx.block_size = block_size before inspecting the return code. init_block_ctx() sets the caller's pointer to NULL and returns -ENOMEM when no entry of the static block1_contexts[] pool is free or timed out, so that store dereferences a NULL pointer.\n\nThe pool holds CONFIG_LWM2M_NUM_BLOCK1_CONTEXT entries (default 3) and an entry is only reclaimed once its transfer completes, fails, or ages past 30 seconds. A peer that reaches the client's LwM2M socket can therefore start three block-wise writes on three distinct object paths with the CoAP More bit set and leave them incomplete, then send the first block of a fourth write on a new path to reach the unguarded dereference. Reachability is gated only by the connected UDP socket's source-address filter unless CONFIG_LWM2M_DTLS_SUPPORT is enabled — which has no default — so in a NoSec deployment an on-path or address-spoofing attacker needs no credentials; the same sequence is also reachable from a bootstrap or lower-trust server, and can be hit accidentally by a legitimate server running four concurrent block transfers.\n\nThe write targets a fixed low address with a value between 0 and 7, so the consequence is a fatal memory fault (BusFault or corrupted low memory leading to a fault) rather than a usable memory-corruption primitive: the device crashes or resets. Confidentiality and integrity are not affected. The fix moves the store below the guard and validates the context pointer itself instead of the return code, so the context is only touched once it is known to be valid.","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":"NULL pointer dereference in Zephyr LwM2M client when the CoAP Block1 context pool is exhausted","id":"CVE-2026-18746","indexable":true,"kev":null,"kind":"cve","links":{"ecosystem":null,"product":null,"products":[],"type":"null_dereference","year":"2026"},"n_packages":0,"n_references":2,"next":{"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"},"packages":[],"prev":{"headline":"This CVE ID has been rejected or withdrawn by its CVE Numbering Authority.","id":"CVE-2026-18745"},"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 attacker can crash a Zephyr LwM2M client by exhausting the CoAP Block1 context pool, causing a null pointer dereference and device reset.","url":"https://insights.sbomify.com/CVE-2026-18746/"}