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CVE-2026-71263— FreeModbus LINUXTCP Port Off-by-One Global Buffer Overflow in xMBPortTCPPool()

Quick assessment

Affected
cwalter-at FreeModbus
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Dr. techn. Christian Walter FreeModbus Library是Dr. techn. Christian Walter个人开发者开源的一个Modbus协议通信库。 Dr. techn. Christian Walter FreeModbus Library存在缓冲区错误漏洞，该漏洞源于demo/LINUXTCP/port/porttcp.c文件中的xMBPortTCPPool()函数边界检查不当，使用了严格大于比较而非大于等于，导致缓冲区溢出，可能造成内存破坏。攻击者可通过发

CVSS 9.1 · Critical EPSS 0.28% · P21

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
cwalter-at FreeModbus ≤ * affected
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I. Basic Information for CVE-2026-71263

Vulnerability Information
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Vulnerability Title
FreeModbus LINUXTCP Port Off-by-One Global Buffer Overflow in xMBPortTCPPool()
Source: CVE Program / CVE List V5
Vulnerability Description
The LINUXTCP port of FreeModbus contains an off-by-one bounds check in xMBPortTCPPool (demo/LINUXTCP/port/porttcp.c). The check uses a strict greater-than comparison instead of greater-than-or-equal against the 263-byte MB_TCP_BUF_SIZE limit.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
跨界内存写
Source: CVE Program / CVE List V5
Vulnerability Title
Dr. techn. Christian Walter FreeModbus Library 缓冲区错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Dr. techn. Christian Walter FreeModbus Library是Dr. techn. Christian Walter个人开发者开源的一个Modbus协议通信库。 Dr. techn. Christian Walter FreeModbus Library存在缓冲区错误漏洞，该漏洞源于demo/LINUXTCP/port/porttcp.c文件中的xMBPortTCPPool()函数边界检查不当，使用了严格大于比较而非大于等于，导致缓冲区溢出，可能造成内存破坏。攻击者可通过发
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
cwalter-at FreeModbus 0 ~ * -

II. Public POCs for CVE-2026-71263

# POC Description Source Link Shenlong Link
AI-Generated POC Premium
Qwen3.6-35B-A3B · 10105 chars
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Vulnerability reproduction recording (real sandbox build + trigger, exclusive)
In-depth vulnerability mechanism
Trigger conditions & impact
Full executable POC code
Exploit chain & mitigation
POC zip download
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III. Intelligence Information for CVE-2026-71263

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Other References for CVE-2026-71263 (2)

IV. Related Vulnerabilities

Same weakness: CWE-787

V. Comments for CVE-2026-71263

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