CVE-2026-1998: MicroPython Use-After-Free Vulnerability

CVE-2026-1998 Overview

A memory corruption vulnerability has been identified in MicroPython versions up to 1.27.0. This flaw exists within the mp_import_all function located in the file py/runtime.c. When exploited, the vulnerability allows an attacker with local access to cause memory corruption, potentially leading to denial of service or other undefined behavior. The exploit methodology has been disclosed publicly, and a patch has been made available to address this issue.

Critical Impact

Local attackers can exploit the mp_import_all function to cause memory corruption in MicroPython applications, affecting embedded systems and IoT devices running the vulnerable runtime.

Affected Products

• MicroPython versions up to and including 1.27.0
• Systems running MicroPython runtime environment
• Embedded devices and IoT applications using vulnerable MicroPython builds

Discovery Timeline

• February 6, 2026 - CVE-2026-1998 published to NVD
• February 6, 2026 - Last updated in NVD database

Technical Details for CVE-2026-1998

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw resides in the mp_import_all function within py/runtime.c, which is responsible for handling import operations in the MicroPython runtime. When specially crafted input is processed, the function fails to properly validate memory boundaries, resulting in memory corruption.

The local attack vector requires an attacker to have access to the system running MicroPython, where they can execute malicious code that triggers the vulnerable function. While the impact is primarily limited to availability (causing crashes or denial of service), memory corruption vulnerabilities can sometimes be leveraged for more severe exploits depending on the execution context.

Root Cause

The root cause of CVE-2026-1998 stems from improper bounds checking within the mp_import_all function in py/runtime.c. The function does not adequately validate the boundaries of memory operations during the import process, allowing malformed or unexpected input to write beyond allocated memory regions. This lack of proper input validation and memory management leads to the memory corruption condition.

Attack Vector

The attack requires local access to the system running MicroPython. An attacker must be able to execute Python code within the MicroPython environment to trigger the vulnerable mp_import_all function. The exploitation involves crafting specific import statements or module manipulations that cause the function to mishandle memory operations.

The vulnerability mechanism involves improper memory boundary validation in the import handling logic. When the mp_import_all function processes certain inputs, it fails to properly restrict operations within the bounds of allocated memory buffers. Technical details and the specific triggering conditions can be found in the GitHub Issue Discussion and the associated GitHub Pull Request.

Detection Methods for CVE-2026-1998

Indicators of Compromise

• Unexpected crashes or segmentation faults in MicroPython applications during module import operations
• Memory-related error messages originating from py/runtime.c or the mp_import_all function
• Unusual memory consumption patterns in MicroPython processes
• Application instability when processing untrusted Python code

Detection Strategies

• Monitor MicroPython runtime logs for memory allocation failures or corruption warnings
• Implement runtime monitoring for abnormal behavior in embedded devices running MicroPython
• Use memory sanitizers (such as AddressSanitizer) during development and testing to detect memory corruption issues
• Audit code paths that invoke mp_import_all or perform wildcard imports

Monitoring Recommendations

• Deploy application-level monitoring to detect crashes in MicroPython-based services
• Implement watchdog processes to restart services affected by memory corruption crashes
• Log and alert on repeated failures in module import operations
• Review system logs for patterns consistent with memory corruption exploitation attempts

How to Mitigate CVE-2026-1998

Immediate Actions Required

• Update MicroPython to a version that includes patch 570744d06c5ba9dba59b4c3f432ca4f0abd396b6
• Restrict local access to systems running vulnerable MicroPython versions
• Avoid processing untrusted Python code on affected systems until patched
• Implement input validation for any externally-sourced modules or code

Patch Information

A patch has been released to address this vulnerability. The fix is available in commit 570744d06c5ba9dba59b4c3f432ca4f0abd396b6 in the MicroPython repository. Organizations should apply this patch or upgrade to a version that incorporates the fix. The patch can be reviewed at the GitHub Commit Changes page.

Workarounds

• Limit execution of untrusted code within MicroPython environments until the patch is applied
• Implement sandboxing or isolation mechanisms for MicroPython runtime processes
• Restrict the use of wildcard imports (from module import *) in production environments where possible
• Consider deploying MicroPython in containerized environments to limit the impact of potential exploitation

# Apply the security patch from source
cd micropython
git fetch origin
git cherry-pick 570744d06c5ba9dba59b4c3f432ca4f0abd396b6
make clean
make