CVE-2026-76788
8.8HighPublished 19 Oct 2026 · NVD status: Received · AI triage by gemini-3.8-flash
- Attack vector
- Adjacent network
- Complexity
- Low
- Privileges needed
- None
- User interaction
- None
- Impact
- Full C/I/A compromise
- Weakness
- CWE-787
Impact
Attackers with access to the RS-485 bus or a compromised peripheral can crash the access-control panel or hijack control flow in the OSDP receive thread. They need local RS-485 bus access to inject crafted unauthenticated or plaintext OSDP replies.
Root cause
The OSDP Control Panel reply parser fails to validate payload lengths for REPLY_KEYPPAD and REPLY_RAW against the fixed 64-byte destination buffers before calling memcpy(), causing a stack buffer overflow.
Affected systems
Zephyr RTOS built with CONFIG_OSDP and CONFIG_OSDP_MODE_CP; exact release versions are not listed — check the vendor advisory.
CVSS v3.1 · CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Fix & remediation
Apply Zephyr commit f10d55f47c6970e95d3a7c6ba08e6adec3c79acd to enforce the OSDP_EVENT_MAX_DATALEN bound on incoming replies. As an interim mitigation, physically secure the RS-485 bus wiring and isolate peripheral devices.
AI-suggested. Run it in staging first and check it against the vendor advisory. Why?
NVD description
The OSDP Control Panel reply parser cp_decode_response() in subsys/mgmt/osdp/src/osdp_cp.c decodes replies from a Peripheral Device into a stack-allocated struct osdp_event. For the REPLY_KEYPPAD and REPLY_RAW reply types, the payload length is taken from the received frame and the only validation performed is that the declared length is self-consistent with the number of payload bytes present in the frame. Because the attacker controls both the length field and the frame length, that check imposes no bound, and the subsequent memcpy() writes into the fixed 64-byte data arrays of struct osdp_event_keypress / struct osdp_event_cardread (OSDP_EVENT_MAX_DATALEN). The sibling REPLY_FMT handler in the same switch already carried the missing > OSDP_EVENT_MAX_DATALEN bound. The defect is reached from cp_process_reply(), which reads bytes from the OSDP RS-485 channel and passes them through osdp_phy_check_packet() and osdp_phy_decode_packet() before dispatching on the reply ID. Triggering it requires CONFIG_OSDP with CONFIG_OSDP_MODE_CP and an application event callback registered (the normal Control Panel integration), plus a frame carrying a correct SOM, a valid CRC-16, and a matching 2-bit sequence number — all of which are computable or observable by anyone on the bus. No check ties the reply ID to the outstanding command, so an oversized REPLY_KEYPPAD or REPLY_RAW is accepted as the answer to a routine CMD_POLL. A malicious or compromised card reader, or anyone with access to the RS-485 wiring, can supply such a frame; CONFIG_OSDP_SC_ENABLED only helps while a secure channel is active, and a single unauthenticated frame carrying a bad MAC causes sc_deactivate(), after which plaintext replies are again accepted. With the default CONFIG_OSDP_UART_BUFFER_LENGTH of 256, roughly 180 bytes of fully attacker-chosen data can be written past the end of the stack-allocated event object, over saved registers and the return address on typical Cortex-M and RISC-V frame layouts (Zephyr does not enable stack canaries by default). The impact ranges from a hard crash of the access-control panel to potential control-flow hijack in the context of the OSDP receive thread. The fix adds an OSDP_EVENT_MAX_DATALEN bound to both handlers, capping each memcpy() at the size of its destination.