Stack out-of-bounds write in the OSDP Control Panel reply parser

Summary

CVE	CVE-2026-76788
State	PUBLISHED
Assigner	zephyr
Source Priority	CVE Program / NVD first with legacy fallback
Published	2026-10-19 21:18:01 UTC
Updated	2026-10-19 21:18:01 UTC
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.

Risk And Classification

Primary CVSS: v3.1 8.8 HIGH from [email protected]

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Problem Types: CWE-787 | CWE-787 bounds

Version	Source	Type	Score	Severity	Vector
3.1	[email protected]	Secondary	8.8	HIGH	`CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`
3.1	CNA	CVSS	8.8	HIGH	`CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`

CVSS v3.1 Breakdown

Attack Vector

Adjacent

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Vendor Declared Affected Products

Source	Vendor	Product	Version	Platforms
CNA	Zephyrproject	Zephyr	affected 3.3.0 4.4.2 semver	Not specified

References

Reference	Source	Link	Tags
github.com/zephyrproject-rtos/zephyr/commit/f10d55f47c6970e95d3a7c6ba08e...	[email protected]	github.com
github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-fgg7-h8p9-...	[email protected]	github.com
CVE Program record	CVE.ORG	www.cve.org	canonical
NVD vulnerability detail	NVD	nvd.nist.gov	canonical, analysis

No vendor comments have been submitted for this CVE.

There are currently no legacy QID mappings associated with this CVE.