CVE-2025-53470: Apache NimBLE Buffer Overflow Vulnerability

CVE-2025-53470 Overview

CVE-2025-53470 is an out-of-bounds read vulnerability affecting the Apache NimBLE HCI H4 driver. The vulnerability occurs when specially crafted HCI events are processed, leading to invalid memory reads in the H4 driver. This flaw allows an attacker with adjacent network access to potentially read sensitive memory contents through malicious Bluetooth HCI packets.

Critical Impact

While rated as low severity, this out-of-bounds read vulnerability could expose sensitive memory contents when exploited through a malicious or compromised Bluetooth controller. Organizations using Apache NimBLE in IoT and embedded Bluetooth implementations should prioritize upgrading to version 1.9.

Affected Products

• Apache NimBLE through version 1.8
• NimBLE HCI H4 transport driver implementations
• Embedded systems and IoT devices utilizing the vulnerable NimBLE Bluetooth stack

Discovery Timeline

• 2026-01-10 - CVE CVE-2025-53470 published to NVD
• 2026-01-13 - Last updated in NVD database

Technical Details for CVE-2025-53470

Vulnerability Analysis

The vulnerability resides in the HCI H4 driver component of Apache NimBLE, specifically in the event parsing logic within hci_h4.c. When the driver receives HCI events, it calculates the expected length of incoming data based on header information. Prior to the fix, the driver did not validate whether the expected event length exceeded the configured buffer size (BLE_TRANSPORT_EVT_SIZE), allowing oversized events to trigger out-of-bounds memory reads.

This vulnerability requires an attacker to have access to a malicious or compromised Bluetooth controller that can send specially crafted HCI events. The attack vector is adjacent network (Bluetooth proximity), requiring the attacker to be within Bluetooth range of the target device. The complexity is considered high because exploitation requires control over the Bluetooth controller hardware or firmware.

Root Cause

The root cause is a missing bounds check in the H4 transport layer's event parsing routine. When processing HCI events, the driver reads the expected payload length from the event header (h4sm->hdr[1] + 2) but fails to validate this value against the maximum allowed event size before proceeding with memory operations. This oversight allows an attacker-controlled length value to cause the driver to read beyond allocated buffer boundaries (CWE-125: Out-of-bounds Read).

Attack Vector

The attack requires an adjacent network position (Bluetooth proximity) and involves sending malformed HCI events through a compromised or malicious Bluetooth controller. The attacker must:

1. Gain control over a Bluetooth controller that communicates with the target device running Apache NimBLE
2. Craft HCI events with header length values exceeding BLE_TRANSPORT_EVT_SIZE
3. Send these malformed events to trigger out-of-bounds memory reads in the H4 driver

The following patch addresses the vulnerability by adding proper bounds checking:

         }
 
         h4sm->exp_len = h4sm->hdr[1] + 2;
+        if (h4sm->exp_len > MYNEWT_VAL(BLE_TRANSPORT_EVT_SIZE)) {
+            return -1;
+        }
         break;
     case HCI_H4_ISO:
         assert(h4sm->allocs && h4sm->allocs->iso);

Source: GitHub Commit Update

Detection Methods for CVE-2025-53470

Indicators of Compromise

• Unexpected crashes or memory access violations in Bluetooth-enabled devices running Apache NimBLE
• Anomalous HCI event traffic with unusually large length values in event headers
• System logs indicating invalid memory access errors originating from the HCI H4 driver
• Bluetooth controller firmware exhibiting unexpected behavior or sending malformed packets

Detection Strategies

• Monitor Bluetooth HCI traffic for events with length fields exceeding expected maximum values
• Implement memory access monitoring on embedded systems to detect out-of-bounds read attempts
• Deploy runtime memory protection mechanisms that can identify and alert on invalid memory accesses
• Review system crash dumps for patterns indicating exploitation of the H4 driver vulnerability

Monitoring Recommendations

• Enable verbose logging for the NimBLE Bluetooth stack to capture HCI event processing details
• Implement watchdog mechanisms to detect and recover from driver crashes caused by malformed events
• Monitor firmware integrity of connected Bluetooth controllers for unauthorized modifications
• Track Apache NimBLE version deployments across the organization to identify vulnerable instances

How to Mitigate CVE-2025-53470

Immediate Actions Required

• Upgrade Apache NimBLE to version 1.9 or later, which includes the security fix
• Audit all deployed devices and systems using Apache NimBLE to identify vulnerable versions
• Restrict physical access to Bluetooth-enabled devices in sensitive environments
• Consider temporarily disabling Bluetooth functionality on critical systems until patches are applied

Patch Information

Apache has released version 1.9 of NimBLE which addresses this vulnerability. The fix adds a bounds check to validate that received HCI events do not exceed the configured BLE_TRANSPORT_EVT_SIZE buffer. The patch is available via the GitHub Commit Update. Additional details can be found in the Apache Mailing List Thread and the OpenWall OSS-Security Post.

Workarounds

• Use only trusted and verified Bluetooth controllers from reputable manufacturers
• Implement network segmentation to isolate Bluetooth-enabled devices from critical systems
• Disable Bluetooth functionality entirely on devices where it is not required
• Apply defense-in-depth measures including memory protection features available on the target platform

# Verify NimBLE version and update to patched release
# Check current version in your project configuration
grep -r "NIMBLE_VERSION" ./nimble/

# Update to version 1.9 or later
# For Apache Mynewt projects, update the dependency in project.yml
# pkg.deps:
#     - "@apache-mynewt-nimble/nimble"
# Then rebuild with the latest version
newt upgrade
newt build <target>