CVE-2026-12520
MediumCVSS 6.4Exploitation Probability (EPSS)
Low risk22th percentile - higher than 22% of all known CVEs
Summary
The Sierra Wireless HL7800 cellular modem driver (up to v4.4.0) contains a vulnerability involving out-of-bounds writes on the stack while parsing AT responses. Most handlers write a NUL terminator one byte past the end of a 128-byte buffer, while the +KCELLMEAS handler allows a full stack buffer overflow with data from response lines longer than 128 bytes.
Risk Assessment
An attacker (e.g., a rogue base station, compromised modem baseband, or remote peer) can cause kernel memory corruption, potentially leading to arbitrary code execution in kernel context or at least a reliable system crash.
Recommendation
Update the modem driver to a patched version that uses sizeof(dst)-1 as the destination size and adds proper bounds for IMSI and +KCELLMEAS fields. If patching is not possible, limit the modem's exposure to untrusted cellular networks.
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Original NVD description (English source)
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.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS