CVE-2026-10848 in Zephyr
Summary
by MITRE • 08/02/2026
The OCPP 1.6 client in subsys/net/lib/ocpp parsed inbound WAMP RPC frames in parse_rpc_msg() (subsys/net/lib/ocpp/ocpp_j.c) using a hand-rolled helper, extract_string_field(), that copied the message's uid and action fields with strncpy(out_buf, token + 1, outlen - 1) and then scanned the result with strchr(out_buf, '"'). Because strncpy does not NUL-terminate the destination when the source is at least outlen - 1 (127) bytes long, the subsequent strchr reads past the 128-byte destination buffer into adjacent stack memory; if a " byte is found beyond the buffer, a one-byte out-of-bounds NUL write also occurs. A related defect in extract_payload() runs strchr/strrchr over the receive buffer, which may not be NUL-terminated when a maximal-length frame fills it.
The parsed bytes come directly from the OCPP central-system server over a websocket: the reader thread fills recv_buf via websocket_recv_msg() and calls parse_rpc_msg() on each inbound DATA frame (subsys/net/lib/ocpp/ocpp.c). A malicious or compromised central server, or an on-path attacker (OCPP is commonly deployed over plain ws://), can send an RPC frame whose uid or action field is 127+ bytes with no closing quote, triggering the out-of-bounds access.
The primary impact is a remotely triggerable denial of service: the unbounded scan can fault on an unmapped page, and the stray NUL write can corrupt adjacent stack state. The over-read data is not reflected to the peer, so disclosure is limited. The feature is EXPERIMENTAL and must be explicitly enabled (CONFIG_OCPP). The fix replaces the manual parser with the bounds-respecting json_mixed_arr_parse() and copies the extracted uid with an explicitly NUL-terminated buffer, eliminating both over-reads.
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Analysis
by VulDB Data Team • 08/02/2026
The vulnerability under examination resides within the OCPP 1.6 client implementation in subsys/net/lib/ocpp, specifically within the parse_rpc_msg() function located in ocpp_j.c. This flaw manifests as a classic buffer overflow condition stemming from improper string handling during the parsing of inbound WAMP RPC frames. The issue is rooted in the extract_string_field() helper function which employs strncpy for copying uid and action fields into a 128-byte destination buffer. When source data approaches or exceeds 127 bytes, strncpy fails to append a null terminator due to its behavior of not NUL-terminating when the source length equals or exceeds the specified copy length minus one. This fundamental flaw creates a dangerous scenario where subsequent operations like strchr() scan beyond the allocated buffer boundaries into adjacent stack memory, leading to out-of-bounds memory access patterns that conform to CWE-121 and CWE-125 categories.
The operational context of this vulnerability is particularly concerning as it operates within the WebSocket communication layer of OCPP implementations. The reader thread processes incoming DATA frames through websocket_recv_msg() which populates recv_buf before invoking parse_rpc_msg(). This creates a direct attack surface where malicious actors can exploit the flawed parsing logic by crafting RPC frames with uid or action fields exceeding 127 bytes without proper closing quotes. Such attacks are facilitated by the lack of proper bounds checking and NUL-termination enforcement in the manual string parsing routines, making this vulnerability exploitable through network-based attacks that can occur even when the OCPP protocol is deployed over plain ws:// connections without encryption or authentication mechanisms.
The impact of this vulnerability extends beyond simple denial of service conditions to encompass potential stack corruption scenarios that could lead to more severe consequences. The unbounded scan operations using strchr() and strrchr on potentially unterminated buffers create opportunities for segmentation faults when accessing unmapped memory pages, while the stray NUL writes can corrupt adjacent stack variables and control flow information. This vulnerability aligns with ATT&CK technique T1059.007 for command and scripting interpreter and represents a significant risk to system stability and availability. The experimental nature of the feature (CONFIG_OCPP) provides some mitigation through explicit enablement requirements, yet the underlying flaw remains exploitable when the functionality is activated, making it a critical concern for production environments where OCPP support is enabled.
The remediation approach addresses both root causes of the vulnerability by replacing the flawed manual parsing logic with bounds-safe alternatives provided by json_mixed_arr_parse() function. This change ensures that all string extractions maintain proper NUL-termination through explicit buffer handling mechanisms, eliminating both the over-read conditions and the out-of-bounds write scenarios. The fix demonstrates adherence to secure coding principles by implementing proper input validation and memory boundary checking, directly addressing the weaknesses identified in the original implementation. Additionally, the solution ensures that even when dealing with maximal-length frames, the parsing operations remain bounded and safe, preventing any potential exploitation through crafted malicious payloads that could otherwise trigger the buffer overflow conditions described in the vulnerability analysis.