CVE-2025-53477: Apache NimBLE NULL Pointer Vulnerability

CVE-2025-53477 Overview

CVE-2025-53477 is a NULL Pointer Dereference vulnerability discovered in Apache NimBLE, a popular open-source Bluetooth Low Energy (BLE) stack. The vulnerability stems from missing validation of HCI (Host Controller Interface) connection complete events or HCI command TX buffer operations, which could lead to a NULL pointer dereference condition.

This vulnerability is classified under CWE-476 (NULL Pointer Dereference) and can result in denial of service conditions when exploited. The issue specifically requires disabled asserts and a broken or malicious Bluetooth controller to trigger, which limits the practical attack surface but still presents a risk in certain deployment scenarios.

Critical Impact

Successful exploitation can cause application crashes and denial of service in IoT devices and embedded systems using Apache NimBLE through version 1.8.0.

Affected Products

• Apache NimBLE through version 1.8.0
• IoT devices and embedded systems utilizing the Apache mynewt-nimble Bluetooth stack
• Applications built on Apache NimBLE with disabled runtime assertions

Discovery Timeline

• 2026-01-10 - CVE CVE-2025-53477 published to NVD
• 2026-01-13 - Last updated in NVD database

Technical Details for CVE-2025-53477

Vulnerability Analysis

The vulnerability exists in Apache NimBLE's handling of HCI (Host Controller Interface) events and command transmission buffers. When the Bluetooth stack processes incoming HCI connection complete events or prepares HCI command TX buffers, the code fails to properly validate that the associated memory pointers are non-NULL before dereferencing them.

In a typical scenario, the BLE stack allocates buffers for HCI operations and maintains pointers to these structures. However, under certain conditions—particularly when runtime assertions are disabled during compilation and when interacting with a malfunctioning or malicious Bluetooth controller—these pointers may remain uninitialized or become invalidated. The subsequent dereference of a NULL pointer causes the application to crash, resulting in denial of service.

The exploitation scenario requires specific preconditions: the target system must have been compiled with assertions disabled (which removes safety checks), and the Bluetooth controller must behave unexpectedly by sending malformed or out-of-sequence HCI events. This combination of factors limits widespread exploitation but poses real risks in production environments where assertions are commonly disabled for performance reasons.

Root Cause

The root cause is insufficient input validation in the HCI event handling and command transmission pathways within Apache NimBLE. The code assumes that buffers and connection structures will always be properly initialized when HCI events arrive, but does not defensively verify pointer validity before use. When assertions are disabled during compilation (a common practice in production builds), the safety net provided by assert() statements is removed, exposing the underlying NULL pointer dereference vulnerability.

Attack Vector

The attack vector is network-based, exploitable through the Bluetooth interface. An attacker with a malicious or specially crafted Bluetooth controller could send unexpected HCI responses or connection complete events that trigger the vulnerable code path. The attack requires:

1. Physical proximity within Bluetooth range of the target device
2. A modified or malicious Bluetooth controller capable of generating malformed HCI responses
3. A target device running Apache NimBLE version 1.8.0 or earlier with disabled assertions

While the attack requires specific conditions, compromised or rogue Bluetooth adapters could potentially be used in targeted attacks against IoT devices, medical equipment, or industrial systems running the vulnerable NimBLE stack. The denial of service impact could be particularly severe in safety-critical embedded applications.

Detection Methods for CVE-2025-53477

Indicators of Compromise

• Unexpected application crashes or device reboots in systems using Apache NimBLE for Bluetooth connectivity
• Core dumps or crash logs showing NULL pointer dereference in HCI-related functions
• Unusual Bluetooth controller behavior or connection anomalies preceding crashes
• Repeated crash patterns correlating with Bluetooth pairing or connection events

Detection Strategies

• Monitor system logs and crash reports for NULL pointer dereference exceptions in NimBLE-related processes
• Implement runtime monitoring for abnormal Bluetooth HCI event patterns
• Deploy application stability monitoring to detect crash loops in BLE-enabled services
• Review build configurations to identify deployments with disabled assertions

Monitoring Recommendations

• Enable crash reporting and telemetry on IoT devices running Apache NimBLE
• Implement watchdog timers to detect and recover from denial of service conditions
• Log all Bluetooth connection events and HCI command sequences for forensic analysis
• Monitor device availability metrics to identify potential DoS attack patterns

How to Mitigate CVE-2025-53477

Immediate Actions Required

• Upgrade Apache NimBLE to version 1.9.0 or later, which contains the security fix
• Review and update all IoT devices and embedded systems using the affected NimBLE versions
• Consider enabling runtime assertions in high-security deployments as a defense-in-depth measure
• Assess exposure of Bluetooth-enabled devices to untrusted environments

Patch Information

Apache has released version 1.9.0 of NimBLE which addresses this vulnerability. The fix adds proper NULL pointer validation before dereferencing HCI connection and command buffer pointers. Two commits have been published addressing this issue:

• GitHub Commit 0caf9ba
• GitHub Commit 3160b8c

Additional details are available in the Apache Mailing List Discussion and the OpenWall OSS Security Post.

Workarounds

• If immediate patching is not possible, consider enabling runtime assertions (NDEBUG not defined) during compilation to activate safety checks
• Restrict physical access to Bluetooth-enabled devices in sensitive environments
• Implement application-level watchdog mechanisms to recover from potential crashes
• Consider disabling Bluetooth functionality on affected devices if not required for operations

# Configuration example for upgrading Apache NimBLE
# Clone the latest NimBLE repository with the security fix
git clone https://github.com/apache/mynewt-nimble.git
cd mynewt-nimble
git checkout nimble_1_9_0_tag

# Rebuild your project with the patched NimBLE version
# Ensure assertions are enabled for additional protection
CFLAGS="-UNDEBUG" make rebuild