Description

The WNC-M14A2A LTE-M modem driver mishandles unsolicited %NOTIFYEV: events in on_cmd_socknotifyev() (drivers/modem/vendor_standalone/wncm14a2a.c). The response line is linearized into a fixed 40-byte stack buffer via net_buf_linearize(), which caps the copy at 39 bytes and returns out_len <= 39. The two quote-delimiter scanning loops, however, were bounded by len — the full CR/LF-delimited frame length returned by net_buf_findcrlf() — rather than by out_len. When a %NOTIFYEV: line longer than 39 bytes contains no " within the linearized region, the loop indices p1/p2 walk past value[39] and read adjacent stack memory until a stray quote byte is found or the index reaches len. The over-read string is then passed to strncmp()/atoi()/LOG_*, and if a quote byte is found out of bounds the subsequent value[p2] = '\0' performs a single-NUL out-of-bounds stack write at an attacker-influenced offset. The %NOTIFYEV: payload carries network-derived content (LTIME network time, SIB1 base-station system information, CSPS/RRCSTATE), so a rogue cellular base station, a malicious or compromised modem module, or RF manipulation that induces an over-long notify line reaches the defect without any application interaction; the handler runs automatically on the unsolicited event in the modem RX thread. The impact is out-of-bounds stack disclosure (into logs and parsing) and stack corruption that can crash the modem RX thread (denial of service). The write offset is only weakly controlled, so memory-safe code execution is not demonstrated. The fix bounds both scanning loops by out_len, keeping all accesses within the linearized buffer.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "5.0",
  "pubDate": "2026-08-17T17:16:38.867Z",
  "pubdate": "2026-08-17T17:16:38.867Z",
  "executiveSummary": "The WNC-M14A2A LTE-M modem driver contains a stack-based buffer overflow and out-of-bounds read vulnerability within the unsolicited event handling logic. The vulnerability stems from improper bounds checking during the processing of %NOTIFYEV: events in drivers/modem/vendor_standalone/wncm14a2a.c. Specifically, the response line is copied into a fixed 40-byte stack buffer using net_buf_linearize(), which restricts the copy operation to a maximum of 39 bytes. However, subsequent quote-delimiter scanning loops incorrectly use the full frame length instead of the linearized length. When a crafted %NOTIFYEV: payload exceeds 39 bytes without containing a quote character within the valid region, the loops traverse past the boundary of the stack buffer. This results in out-of-bounds stack memory disclosure via logs and parsing functions, as well as a single-NUL out-of-bounds stack write if a stray quote byte is located out of bounds. The attack vector is network-derived, enabling a rogue cellular base station, compromised modem module, or malicious RF manipulation to trigger the defect automatically within the modem RX thread without requiring application interaction or authentication. The impact includes out-of-bounds stack data disclosure and denial of service through stack corruption that crashes the modem RX thread.",
  "technicalDetails": "The vulnerability resides in the WNC-M14A2A modem driver function on_cmd_socknotifyev() located in drivers/modem/vendor_standalone/wncm14a2a.c. The root cause is a discrepancy between the copy mechanism's upper bound and the parsing loops' boundary conditions. When the modem receives an unsolicited %NOTIFYEV: event, the frame is returned by net_buf_findcrlf() with a CR/LF-delimited length denoted as len. The driver then invokes net_buf_linearize() to copy the response line into a fixed 40-byte stack buffer named value. Because net_buf_linearize() caps the copy operation at 39 bytes and returns an out_len <= 39, the actual safe operating region is strictly bounded by out_len. Despite this, the two quote-delimiter scanning loops intended to parse the payload use len instead of out_len as their termination condition.\nDuring step-by-step exploitation, an attacker capable of delivering a %NOTIFYEV: payload longer than 39 bytes—such as via a rogue cellular base station broadcasting malicious network-derived content including LTIME network time, SIB1 base-station system information, or CSPS/RRCSTATE parameters—triggers the vulnerable code path automatically upon receiving the unsolicited event in the modem RX thread. If the input payload lacks a quote character (\" ) within the first 39 bytes, the scanning loop indices p1 and p2 increment past the terminal index value[39] of the fixed stack buffer. Consequently, the execution context reads adjacent stack memory sequentially until either a stray quote byte is encountered or the index reaches the full frame length len. The resulting over-read string is subsequently passed to functions such as strncmp(), atoi(), and various logging mechanisms (LOG_*), leading to arbitrary stack memory disclosure.\nFurthermore, if a quote byte is encountered during the out-of-bounds traversal, the subsequent assignment operation value[p2] = '\\0' executes a single-NUL out-of-bounds stack write directly onto adjacent stack memory at an attacker-influenced offset. This corruption of the stack frame can destabilize execution flow and lead to a denial of service by crashing the modem RX thread. While memory-safe code execution is not demonstrated due to the weakly controlled write offset, the combination of information disclosure and thread termination poses a severe reliability risk to the affected system."
}