CVE-2025-48769: Apache NuttX Use After Free Vulnerability

CVE-2025-48769 Overview

A Use After Free vulnerability has been discovered in the fs/vfs/fs_rename code of Apache NuttX RTOS. The flaw stems from a recursive implementation that uses a single buffer referenced by two different pointer variables. This design error allows for arbitrary user-provided size buffer reallocation and subsequent writes to previously freed heap chunks. In specific exploitation scenarios, this could result in unintended virtual filesystem rename or move operation outcomes, potentially compromising system integrity and availability.

This vulnerability affects Apache NuttX RTOS versions from 7.20 through versions prior to 12.11.0. Users who have virtual filesystem based services with write access—especially when exposed over the network via protocols like FTP—are at elevated risk.

Critical Impact

Attackers with low-privilege network access can exploit this Use After Free condition to corrupt heap memory, potentially causing denial of service or unauthorized filesystem modifications in embedded systems running Apache NuttX RTOS.

Affected Products

• Apache NuttX RTOS versions 7.20 through 12.10.x
• Systems exposing virtual filesystem services over the network (e.g., FTP servers)
• Embedded devices and IoT platforms running vulnerable NuttX versions

Discovery Timeline

• 2026-01-01 - CVE CVE-2025-48769 published to NVD
• 2026-01-06 - Last updated in NVD database

Technical Details for CVE-2025-48769

Vulnerability Analysis

The vulnerability exists within the virtual filesystem rename operation (fs_rename) in Apache NuttX RTOS. The core issue is a Use After Free (CWE-416) condition that arises from the recursive nature of the rename function implementation combined with improper buffer management.

When the rename operation is invoked, a single memory buffer is accessed through two different pointer variables. During recursive calls, the buffer can be reallocated with an arbitrary user-provided size while the original pointer still references the freed memory location. Subsequent write operations through the stale pointer corrupt the heap, writing data to memory that has already been freed and potentially reallocated for other purposes.

The vulnerability is particularly dangerous in network-exposed scenarios such as FTP services, where remote authenticated users can trigger the vulnerable code path by performing rename or move operations on the virtual filesystem.

Root Cause

The root cause is a memory management flaw in the recursive implementation of fs/vfs/fs_rename. The function fails to properly synchronize buffer ownership between two pointer variables when the buffer is reallocated during recursive execution. This creates a dangling pointer condition where one variable continues to reference memory that has been freed and potentially reused by subsequent allocations.

The use of a single buffer across recursive calls without proper lifetime management leads to a classic Use After Free scenario. When the buffer is reallocated with attacker-controlled size parameters, the freed memory can be overwritten with attacker-influenced data.

Attack Vector

Exploitation requires network access with low-privilege authentication to a system running affected Apache NuttX RTOS versions. The attack is most feasible through network-exposed virtual filesystem services such as FTP:

1. An attacker authenticates to a network-exposed filesystem service (e.g., FTP server) running on vulnerable NuttX
2. The attacker initiates a rename or move operation designed to trigger the recursive code path
3. By controlling the size parameter during buffer reallocation, the attacker causes the original buffer to be freed
4. The stale pointer writes to the freed memory, corrupting heap metadata or adjacent allocations
5. This corruption can result in denial of service, unintended filesystem modifications, or potentially further memory corruption leading to broader system compromise

The vulnerability mechanism involves heap memory management during the fs_rename operation. When the recursive implementation reallocates a buffer while a stale pointer still references the original allocation, any subsequent write through that pointer corrupts freed memory. For detailed technical analysis, refer to the GitHub NuttX Pull Request which contains the fix.

Detection Methods for CVE-2025-48769

Indicators of Compromise

• Unexpected crashes or service restarts in Apache NuttX RTOS systems, particularly in filesystem-related operations
• Anomalous FTP or virtual filesystem rename/move activity patterns
• Memory corruption errors or heap integrity violations in system logs
• Unusual filesystem state inconsistencies following rename operations

Detection Strategies

• Monitor network-exposed filesystem services for unusual rename or move operation patterns
• Implement intrusion detection rules to flag high volumes of filesystem modification requests from single sources
• Deploy memory integrity monitoring on NuttX-based systems where available
• Audit authentication logs for services exposing virtual filesystem access

Monitoring Recommendations

• Enable verbose logging for FTP and other network filesystem services on NuttX devices
• Monitor for repeated failed or abnormal filesystem operations that could indicate exploitation attempts
• Implement network segmentation to isolate IoT and embedded devices running NuttX from untrusted network segments
• Establish baseline behavior for filesystem operations to detect anomalies

How to Mitigate CVE-2025-48769

Immediate Actions Required

• Upgrade Apache NuttX RTOS to version 12.11.0 or later immediately
• If immediate upgrade is not possible, disable or restrict network access to virtual filesystem services
• Limit authentication credentials for network-exposed filesystem services to essential users only
• Implement network-level access controls to restrict which hosts can connect to affected services

Patch Information

Apache has released version 12.11.0 of NuttX RTOS which addresses this vulnerability. The fix is documented in GitHub Pull Request #16455. Users should upgrade to this version as soon as possible.

For additional details, consult the Apache Mailing List Thread and the Openwall OSS Security Update.

Workarounds

• Disable network-exposed filesystem services such as FTP until patching is complete
• Implement strict firewall rules limiting access to virtual filesystem services to trusted IP addresses only
• If filesystem services must remain active, ensure strong authentication and minimal privilege access
• Monitor systems closely for signs of exploitation while awaiting patch deployment

# Example: Restricting FTP access via firewall (adjust for your environment)
# Only allow specific trusted IP addresses to access FTP service
iptables -A INPUT -p tcp --dport 21 -s 192.168.1.100 -j ACCEPT
iptables -A INPUT -p tcp --dport 21 -j DROP