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CVE-2026-12520— Stack buffer overflow and off-by-one writes in Zephyr HL7800 modem AT response handlers

Quick assessment

Affected
zephyrproject zephyr
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Zephyr是Zephyr组织开源的一款面向物联网的实时操作系统。 Zephyr 2.4.0版本至4.4.2之前版本存在缓冲区错误漏洞，该漏洞源于Sierra Wireless HL7800蜂窝调制解调器驱动解析AT响应时对缓冲区长度验证不当，可能导致栈缓冲区溢出和单字节越界写入，攻击者可利用该漏洞在内核上下文中执行代码或导致系统崩溃。

CVSS 6.4 · Medium EPSS 0.21% · P11

Affected Version Matrix 1

VendorProduct Version RangeStatus
zephyrproject zephyr 2.4.0< 4.4.2 affected
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I. Basic Information for CVE-2026-12520

Vulnerability Information
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Vulnerability Title
Stack buffer overflow and off-by-one writes in Zephyr HL7800 modem AT response handlers
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:A/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
跨界内存写
Source: CVE Program / CVE List V5
Vulnerability Title
Zephyr 缓冲区错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Zephyr是Zephyr组织开源的一款面向物联网的实时操作系统。 Zephyr 2.4.0版本至4.4.2之前版本存在缓冲区错误漏洞，该漏洞源于Sierra Wireless HL7800蜂窝调制解调器驱动解析AT响应时对缓冲区长度验证不当，可能导致栈缓冲区溢出和单字节越界写入，攻击者可利用该漏洞在内核上下文中执行代码或导致系统崩溃。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
zephyrproject zephyr 2.4.0 ~ 4.4.2 -

II. Public POCs for CVE-2026-12520

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III. Intelligence Information for CVE-2026-12520

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Patches & Fixes for CVE-2026-12520 (1)

Vendor Advisories for CVE-2026-12520 (1)

Same Patch Batch · zephyrproject · 2026-08-18 · 3 CVEs total

CVE-2026-12631 6.5 MEDIUM Broken access-control denial in k_thread_join/k_thread_abort syscall validation in Zephyr
CVE-2026-12632 6.5 MEDIUM Out-of-bounds read in Zephyr PTP message parsing from unvalidated message type

IV. Related Vulnerabilities

Same product: zephyr
Same vendor: zephyrproject
Same weakness: CWE-787

V. Comments for CVE-2026-12520

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