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

CVE-2025-48769 Overview

CVE-2025-48769 is a Use After Free vulnerability in the fs/vfs/fs_rename code of the Apache NuttX real-time operating system (RTOS). The flaw stems from a recursive implementation that shares a single buffer between two different pointer variables. An attacker with write access to the virtual filesystem can trigger arbitrary user-controlled buffer reallocation and write into a previously freed heap chunk. The issue affects Apache NuttX RTOS from version 7.20 through versions prior to 12.11.0. Services exposing the virtual filesystem with write access, such as File Transfer Protocol (FTP) servers, are most exposed.

Critical Impact
Network-reachable attackers with low privileges can corrupt heap memory through NuttX FTP or similar VFS write services, causing unintended rename/move operations and potential loss of filesystem integrity and availability.

Affected Products

Apache NuttX RTOS versions 7.20 through 12.10.x
NuttX deployments exposing virtual filesystem write access over the network (e.g., FTP)
Embedded and IoT systems running vulnerable NuttX builds

Discovery Timeline

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

Technical Details for CVE-2025-48769

Vulnerability Analysis

The vulnerability resides in the fs_rename implementation within the NuttX virtual filesystem (VFS) layer. The rename routine uses recursion to traverse path components and relies on a single heap buffer referenced by two distinct pointer variables. During recursive calls, the buffer can be reallocated to an attacker-controlled size while one of the pointers still references the original, now-freed memory region.

This condition meets the classic definition of Use After Free, tracked under [CWE-416]. Subsequent writes through the stale pointer corrupt the newly allocated heap chunk. The result is unintended rename or move semantics in the virtual filesystem, with potential for broader heap corruption depending on allocator state and surrounding objects.

Root Cause

The root cause is improper buffer lifetime management across recursive frames. The function does not refresh or invalidate the secondary pointer after the shared buffer is freed and reallocated. Because the reallocation size is influenced by user-supplied path data, attackers gain control over both the chunk layout and the contents written through the dangling pointer.

Attack Vector

Exploitation requires network reachability to a NuttX service that exposes write access to the VFS. FTP is the canonical example cited in the advisory. An authenticated low-privilege user submits crafted rename or move operations with carefully sized path arguments to drive the recursive code path. The attacker triggers the free, forces reallocation through path length manipulation, and then writes through the stale pointer to corrupt filesystem metadata or adjacent heap objects.

No public proof-of-concept exploit is currently available, and the issue is not listed in the CISA Known Exploited Vulnerabilities catalog.

No verified exploitation code is published. Technical details are available in the upstream fix at Apache NuttX Pull Request #16455 and the OpenWall OSS-Security disclosure.

Detection Methods for CVE-2025-48769

Indicators of Compromise

Unexpected crashes, asserts, or memory faults originating in fs/vfs/fs_rename on NuttX devices
FTP or VFS service sessions issuing unusually long or malformed RNFR/RNTO path arguments
Filesystem entries appearing in unintended locations following rename operations from authenticated users
Repeated rename requests with varied path lengths from a single client, consistent with heap grooming

Detection Strategies

Inspect NuttX build versions across fleet inventory and flag any deployment running 7.20 through 12.10.x
Capture FTP command logs and alert on anomalous rename traffic volumes or oversized path parameters
Monitor device telemetry for kernel asserts, watchdog resets, or VFS errors correlated with rename activity
Apply network intrusion detection signatures against FTP command streams reaching embedded NuttX endpoints

Monitoring Recommendations

Centralize syslog and crash dumps from NuttX devices into a security data lake for correlation
Baseline normal FTP rename behavior per device class and alert on deviations in command size or frequency
Track authentication events for FTP and other VFS-exposing services to identify low-privilege accounts abusing rename operations

How to Mitigate CVE-2025-48769

Immediate Actions Required

Upgrade all Apache NuttX RTOS deployments to version 12.11.0 or later, which contains the upstream fix
Inventory devices exposing FTP or other VFS write services over untrusted networks and prioritize them for patching
Restrict network access to NuttX FTP services using firewalls or network segmentation until patches are applied
Audit and rotate credentials for any low-privilege accounts that can authenticate to VFS-exposing services

Patch Information

The fix is merged in Apache NuttX 12.11.0. Review the upstream change in Apache NuttX Pull Request #16455 and the coordinated disclosure in the Apache mailing list thread. Rebuild and reflash device firmware with the patched NuttX release.

Workarounds

Disable FTP and any other services that expose VFS rename functionality if they are not required
Remove write permissions from VFS-exposing services where feasible, allowing only read-only access
Place vulnerable devices behind a VPN or management network that blocks untrusted clients from reaching FTP ports
Enforce strong authentication and minimize the number of accounts permitted to perform rename operations

bash

# Confirm NuttX version and disable FTP service until patched
# Check the configured NuttX release in your build system
grep CONFIG_VERSION_STRING .config

# Disable FTP in menuconfig if write access is not required
# Networking Support  -> File Transfer Protocol (FTP) server -> [ ] off
make menuconfig

# Rebuild and flash the patched firmware (NuttX >= 12.11.0)
make distclean && ./tools/configure.sh <board>:<config> && make -j