CVE-2019-25656: R i386 Buffer Overflow Vulnerability

CVE-2019-25656 Overview

CVE-2019-25656 is a local buffer overflow vulnerability affecting R i386 version 3.5.0. The vulnerability exists in the GUI Preferences dialog and allows local attackers to trigger a structured exception handler (SEH) overwrite by supplying malicious input. By crafting a payload string in the 'Language for menus and messages' field, attackers can overwrite SEH records and achieve arbitrary code execution.

Critical Impact

This vulnerability enables local attackers to execute arbitrary code, including shellcode, by exploiting the buffer overflow to overwrite SEH records in the R GUI Preferences dialog.

Affected Products

• R i386 3.5.0 (Windows)
• R Project Windows Installation

Discovery Timeline

• 2026-04-05 - CVE CVE-2019-25656 published to NVD
• 2026-04-07 - Last updated in NVD database

Technical Details for CVE-2019-25656

Vulnerability Analysis

This vulnerability is classified as CWE-787 (Out-of-bounds Write), which occurs when the software writes data past the end of a buffer. In the context of CVE-2019-25656, the R i386 GUI Preferences dialog fails to properly validate the length of user-supplied input in the 'Language for menus and messages' field before copying it into a fixed-size buffer on the stack.

The local attack vector means an attacker must have some level of access to the system running R i386 3.5.0. The exploitation requires no user interaction beyond having the vulnerable software installed and accessible. This vulnerability specifically targets the Windows 32-bit (i386) version of R, where the SEH mechanism is used for exception handling.

Root Cause

The root cause of this vulnerability is improper input validation in the GUI Preferences dialog component. When a user enters text in the 'Language for menus and messages' field, the application copies this input into a stack-based buffer without adequate bounds checking. This allows an attacker to supply an oversized string that overflows the buffer and overwrites adjacent memory, including the Structured Exception Handler (SEH) chain stored on the stack.

Attack Vector

The attack is local in nature, requiring the attacker to have access to a system with R i386 3.5.0 installed. The attacker exploits the vulnerability by navigating to the GUI Preferences dialog and entering a specially crafted payload string in the 'Language for menus and messages' input field.

The payload typically consists of:

1. Padding characters to fill the buffer and reach the SEH chain
2. A crafted SEH record containing the address of a POP-POP-RET gadget
3. Shellcode positioned to execute when the exception handler is invoked

When an exception is triggered (either naturally or forced by the overflow), Windows invokes the SEH chain, which now points to attacker-controlled code, resulting in arbitrary code execution. The Exploit-DB #46288 entry provides details on this exploitation technique.

Detection Methods for CVE-2019-25656

Indicators of Compromise

• Unexpected crashes or exceptions in Rgui.exe processes
• Presence of unusually long strings in R configuration files or registry entries related to language preferences
• Evidence of calculator (calc.exe) or other unexpected processes spawning from R GUI processes
• Memory dumps showing SEH chain manipulation in R-related process memory

Detection Strategies

• Monitor for anomalous input lengths in R GUI preference dialogs using endpoint detection tools
• Implement application-level controls that detect buffer overflow attempts in user input fields
• Deploy endpoint protection that monitors for SEH overwrite patterns and exploitation techniques
• Use behavioral analysis to detect shellcode execution originating from the R application process

Monitoring Recommendations

• Enable Windows event logging for application crashes, particularly for Rgui.exe
• Implement process creation monitoring to detect suspicious child processes spawned by R
• Configure SentinelOne to monitor for SEH exploitation patterns in legacy applications
• Review and audit systems for the presence of R i386 3.5.0 installations

How to Mitigate CVE-2019-25656

Immediate Actions Required

• Upgrade R to the latest stable version from the R Project Official Website
• Remove R i386 3.5.0 from systems where it is no longer needed
• Restrict local access to systems running vulnerable R installations
• Implement application allowlisting to prevent unauthorized code execution

Patch Information

Users should upgrade to a newer version of R from the official R Project Windows Installer download page. The VulnCheck Advisory on Buffer Overflow provides additional guidance on remediation. Organizations should prioritize removing or upgrading R i386 3.5.0 installations as part of their vulnerability management program.

Workarounds

• Restrict access to the R GUI Preferences dialog through group policy or application restrictions
• Use the 64-bit version of R where possible, as this vulnerability specifically affects the i386 (32-bit) version
• Deploy endpoint protection solutions like SentinelOne that can detect and block SEH exploitation attempts
• Implement least-privilege access controls to limit which users can modify R preferences