CVE-2026-16512 in Zephyr
Summary
by MITRE • 09/18/2026
gptp_handle_msg() in subsys/net/l2/ethernet/gptp/gptp.c dereferenced the gPTP header returned by GPTP_HDR() and switched on hdr->message_type without first checking that the received frame carries at least sizeof(struct gptp_hdr) (34) bytes of payload. The header accessor gptp_get_hdr() deliberately never fails for a short buffer — it returns pkt->frags->data and leaves validation to its callers — so a truncated frame produced a header pointer covering memory beyond the received data. The per-message-type checks that follow do not compensate: GPTP_VALID_LEN() reduces to len > 60 once the Ethernet header has been pulled, which is false for every fixed-size gPTP message, so GPTP_CHECK_LEN() never rejects a truncated SYNC, FOLLOWUP, PDELAY_RESP or SIGNALING message.
The defect is reached by an unauthenticated peer on the same link sending an Ethernet frame with ethertype 0x88F7 to the PTP multicast address on an interface configured as a gPTP port, with CONFIG_NET_GPTP enabled. Because conformant Ethernet pads frames to 60 bytes, a payload shorter than 34 bytes generally requires a link that can deliver sub-minimum frames — for example the native_sim TAP driver (drivers/ethernet/eth_native_tap.c), which forwards whatever length the host device supplies, or a MAC configured to accept undersized frames.
The short packet is retained (net_pkt_ref() into rcvd_sync_ptr, rcvd_follow_up_ptr, rcvd_pdelay_resp_ptr or rcvd_announce_ptr) and later parsed by the media-dependent and media-independent state machines in subsys/net/l2/ethernet/gptp/gptp_md.c and subsys/net/l2/ethernet/gptp/gptp_mi.c, which read tens of further bytes and copy some of them (the announce priority vector, hdr->port_id) into state that is subsequently transmitted. Under the default fixed-size buffer allocator (CONFIG_NET_BUF_FIXED_DATA_SIZE, 128-byte fragments) the accesses stay inside the allocated fragment and disclose stale recycled buffer contents; under the experimental CONFIG_NET_BUF_VARIABLE_DATA_SIZE allocator, where fragments are heap-allocated at the exact frame length, they are genuine out-of-bounds reads. There is no write and no availability impact.
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Analysis
by VulDB Data Team • 09/18/2026
The vulnerability identified in the gPTP implementation within Zephyr OS represents a critical memory safety flaw rooted in improper input validation during packet processing. Specifically, the function gptp_handle_msg() fails to verify that an incoming Ethernet frame contains sufficient payload data before attempting to parse the Generic Precision Time Protocol header. The code relies on the macro GPTP_HDR(), which is implemented via the helper function gptp_get_hdr(). This accessor deliberately bypasses length checks and simply returns a pointer to the start of the packet fragment's data buffer, assuming that callers will perform necessary validation. However, in this specific instance, no such validation occurs prior to dereferencing the header structure. Consequently, when an attacker sends a truncated Ethernet frame with fewer than thirty-four bytes—the size required for a valid gPTP header—the system interprets memory immediately following the actual packet data as part of the protocol header. This constitutes a classic out-of-bounds read vulnerability where the application accesses memory regions outside the bounds of the allocated buffer associated with the received network packet.
From an operational perspective, this flaw is exploitable by any unauthenticated peer located on the same local area network segment who can craft and transmit Ethernet frames with the ethertype 0x88F7 to the PTP multicast address. While standard Ethernet specifications mandate that valid frames be padded to a minimum of sixty bytes, certain virtualized or specialized networking environments allow for sub-minimum frame transmission. For instance, drivers such as native_sim TAP forward packets exactly as supplied by the host device without enforcing minimum length constraints. When configured with CONFIG_NET_GPTP enabled, the affected system accepts these undersized frames and proceeds to process them through media-dependent and media-independent state machines located in gptp_md.c and gptp_mi.c. These subsequent processing stages attempt to read tens of additional bytes from the malformed header structure, leading to further out-of-bounds memory accesses beyond the initial truncation point.
The security impact of this vulnerability is primarily categorized as an information disclosure risk rather than a denial of service or code execution vector. The nature of the exploit depends heavily on the network buffer allocation strategy employed by the system configuration. Under the default fixed-size buffer allocator, where fragments are allocated with a standard size such as one hundred twenty-eight bytes regardless of actual packet length, the out-of-bounds reads remain confined within the same memory fragment. In this scenario, the attacker can potentially read stale data from previously recycled buffers that have not yet been overwritten by new traffic. This allows for the leakage of sensitive information stored in those buffer slots, such as credentials or internal state variables from prior connections. Conversely, if the system utilizes the experimental variable-size allocator where fragments are heap-allocated to match the exact frame length, the out-of-bounds reads extend into adjacent memory regions entirely unrelated to the packet processing context. This presents a more severe risk of disclosing arbitrary kernel memory contents, although it still does not permit direct writes or immediate service disruption.
This vulnerability aligns with CWE-125, which describes Out-of-Bounds Read vulnerabilities where software accesses data outside the intended buffer boundaries. Furthermore, in terms of attack vectors and techniques, this flaw facilitates reconnaissance activities consistent with ATT&CK technique T1083, File and Directory Discovery, as it enables an attacker to enumerate memory contents that may reveal system configuration or other sensitive details. The lack of write capability means the vulnerability cannot be directly leveraged for remote code execution, but its potential to leak internal state information makes it a significant concern in security-sensitive deployments where precision time protocol is utilized for synchronization across critical infrastructure networks.
To mitigate this risk, immediate remediation should focus on enforcing strict length validation at the earliest possible stage of packet processing. Developers must ensure that gptp_handle_msg() or its underlying helper functions verify that the received frame payload size meets or exceeds sizeof(struct gptp_hdr) before any header fields are accessed. This check should be performed immediately after determining the ethertype and prior to invoking GPTP_HDR(). Additionally, it is advisable to review all packet parsing routines within the networking stack to ensure they adhere to similar defensive coding practices, validating buffer lengths against expected protocol structures. For administrators using variable-size buffers, while this does not eliminate the risk entirely due to potential adjacent memory exposure, reducing reliance on such experimental allocators in production environments may limit the scope of leaked data. Regular security audits and static analysis tools configured to detect out-of-bounds access patterns can also help identify similar flaws across other network protocol implementations within the codebase.