Zephyr Project up to 4.4.1 HL7800 Cellular Modem Driver hl7800.c on_cmd_atcmdinfo_rssi stack-based overflow

Summaryinfo

A vulnerability categorized as very critical has been discovered in Zephyr Project Zephyr up to 4.4.1. Affected by this vulnerability is the function on_cmd_atcmdinfo_rssi of the file drivers/modem/vendor_standalone/hl7800.c of the component HL7800 Cellular Modem Driver. Such manipulation leads to stack-based overflow. This vulnerability is uniquely identified as CVE-2026-12520. The attack can be launched remotely. No exploit exists.

Detailsinfo

A vulnerability, which was classified as very critical, has been found in Zephyr Project Zephyr up to 4.4.1. Affected by this issue is the function on_cmd_atcmdinfo_rssi of the file drivers/modem/vendor_standalone/hl7800.c of the component HL7800 Cellular Modem Driver. The manipulation with an unknown input leads to a stack-based overflow vulnerability. Using CWE to declare the problem leads to CWE-121. A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function). Impacted is confidentiality, integrity, and availability. CVE summarizes:

The Sierra Wireless HL7800 cellular modem driver (drivers/modem/vendor_standalone/hl7800.c, located at drivers/modem/hl7800.c in v4.4.0 and earlier) parses AT responses with roughly twenty handlers that call net_buf_linearize(value, sizeof(value), *buf, 0, len) into a 128-byte stack buffer and then write value[out_len] = 0. Because net_buf_linearize() (lib/net_buf/buf.c) can return a count equal to its destination-length argument, a field that exactly fills the buffer makes the terminating NUL land one byte past the end, a single-byte out-of-bounds write into adjacent stack memory. The +KCELLMEAS cell-measurement handler on_cmd_atcmdinfo_rssi() is worse: it passed the wire length len as the destination size (net_buf_linearize(value, len, *buf, 0, len)), so a response line longer than 128 bytes overflows the value stack buffer with attacker-influenceable content. The line length comes from net_buf_findcrlf(), which accumulates bytes across the whole net_buf fragment chain and is not bounded to 128, so an over-long line reaches the defect. The data originates from the cellular modem over UART, driven by the network: operator-scan results, +CGCONTRDP IP/DNS info, socket indications, and +KCELLMEAS neighbour-cell reports. An attacker able to shape what the modem emits — a rogue base station, a compromised modem baseband, or a remote peer feeding oversized response framing — can drive a line past 128 bytes. The handlers run in the driver's RX thread in kernel context, so the corruption is kernel-side. The +KCELLMEAS path is a full stack buffer overflow whose worst case is code execution in kernel context and whose floor is a reliable crash; the remaining sites are single-byte NUL out-of-bounds writes. Exploitation requires the modem to emit an over-long AT response line, giving high attack complexity over an adjacent (cellular radio) vector. The fix passes sizeof(dst) - 1 (and correct explicit bounds for the IMSI and +KCELLMEAS sites) so the terminator always stays in bounds.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-12520 since 06/17/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 08/18/2026).

Upgrading to version 4.4.2 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-61175). VulDB is the best source for vulnerability data and more expert information about this specific topic.

Productinfo

Type

• Project Management Software

Vendor

• Zephyr Project

Name

• Zephyr

Version

• 4.4.0
• 4.4.1

CPE 2.3info

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CPE 2.2info

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Entryinfo

VulDB is the best source for vulnerability data and more expert information about this specific topic.

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