Apache NimBLE is a lightweight Bluetooth Low Energy (BLE) stack widely used in embedded and IoT environments. It is commonly integrated into firmware running on RTOS-based systems such as FreeRTOS, Zephyr, Apache Mynewt, and bare-metal microcontrollers.
NimBLE is responsible for:
- BLE pairing and bonding
- Encryption and key management
- GATT communication
- Host–controller interaction through HCI
Because NimBLE often runs on devices with no user interface and limited logging, security flaws at this layer can have long-lasting and hard-to-detect impact.
Vulnerability Summary
| Field | CVE-2025-62235 | CVE-2025-53470 |
|---|---|---|
| Vulnerability Type | Authentication bypass | Out-of-bounds read |
| Affected Component | BLE Security Manager (SMP / bonding) | HCI H4 transport parser |
| Affected Versions | Apache NimBLE ≤ 1.8.0 | Apache NimBLE ≤ 1.8.0 |
| Fixed Version | Apache NimBLE 1.9.0 | Apache NimBLE 1.9.0 |
| Attack Vector | Adjacent (BLE radio range) | Local / adjacent (HCI access) |
| Privileges Required | None | Low |
| User Interaction | None | None |
| Primary Impact | Device impersonation, persistent access | Memory disclosure |
| Exploit Practicality | High in real BLE deployments | Moderate, environment-dependent |
| Patch Available | Yes (official) | Yes (official) |
CVE-2025-62235 – BLE Authentication Bypass via Re-Bonding
Description
This vulnerability exists in the BLE pairing and bonding logic. Apache NimBLE allows a remote peer to initiate a new security request even when a bond already exists. Under certain conditions, the stack does not sufficiently verify that the device requesting re-bonding is the same device that originally established trust.
As a result, a malicious BLE device can impersonate a previously bonded peer and silently replace the existing bond.
How the Attack Works
A realistic exploitation flow looks like this:
- A target device has an existing trusted BLE bond (for example, with a phone or gateway).
- An attacker comes within BLE radio range.
- The attacker imitates identifying characteristics used during pairing (address, timing, security flags).
- A crafted BLE Security Request is sent to the target.
- The target accepts the request and removes the original bond.
- A new bond is created with the attacker instead.
No encryption needs to be broken, and in many embedded devices no user approval is required.
Impact
- Unauthorized access to device data
- Ability to read and write GATT characteristics
- Long-term persistence until bonds are manually cleared
- Legitimate device may be locked out permanently
This is especially serious for medical devices, industrial controllers, smart locks, and sensors deployed in the field.
Detection and Monitoring
Useful Log Sources
- BLE Security Manager or SMP logs
- Bond database write/delete events
- Connection and disconnection telemetry
- Firmware debug or audit logs (where available)
Suspicious Behaviors
- Bond deletion followed immediately by new bond creation
- Re-bonding without physical interaction or user approval
- Multiple security requests from the same peer identity
- Bond changes on devices that have been stable for long periods
Example Detection Logic
IF an existing bond is removed
AND a new bond is created within a short time window
AND no user interaction is recorded
THEN flag as possible bond hijacking
MITRE ATT&CK Mapping
- Modify Authentication Process
- Abuse of Trusted Relationships
- Hardware-based or proximity attacks
CVE-2025-53470 – HCI H4 Out-of-Bounds Read
Description
This issue affects the parsing of HCI H4 packets between the BLE controller and the host stack. The NimBLE H4 parser does not fully validate certain length fields before processing them, which can result in the stack reading beyond allocated memory.
The flaw results in memory disclosure, not memory corruption or code execution.
How the Attack Works
This vulnerability is typically exploitable in environments where the attacker can influence HCI traffic, such as:
- Exposed UART or USB debug interfaces
- Development or factory firmware builds
- Use of a malicious or compromised BLE controller
- Physical access to the device
By sending malformed HCI packets with incorrect length values, the attacker can cause the host to read unintended memory regions.
Impact
- Leakage of sensitive in-memory data
- Possible exposure of encryption keys or device identifiers
- Increased effectiveness of follow-on attacks
- Potential instability depending on memory layout
While less severe than the bonding issue, this vulnerability is important in high-assurance or regulated environments.
Detection and Monitoring
Useful Log Sources
- HCI transport logs
- Serial/UART driver logs
- Firmware error counters
- Crash or watchdog reset telemetry
Suspicious Behaviors
- Repeated HCI parsing errors
- HCI packets exceeding expected size limits
- Unexpected resets following malformed traffic
- Abnormal volume of controller-host traffic
Example Detection Logic
IF HCI packet length exceeds defined limits
THEN drop packet and log a security warning
MITRE ATT&CK Mapping
- Data from Local System
- Credentials in Memory
- Abuse of Protocol Parsers
Patch & Remediation
Recommended Action
All users should upgrade to Apache NimBLE version 1.9.0 or later and rebuild firmware using the updated stack.
This release introduces:
- Stronger validation of bond ownership before re-bonding
- Restrictions on silent bond replacement
- Strict length and boundary checks in the HCI H4 parser
Official Patch Links
Apache NimBLE 1.9.0 – Official Release
Fix for CVE-2025-62235 (Bonding / Security Request handling)
Fix for CVE-2025-53470 (HCI H4 length validation)
Post-Patch Validation Checklist
- Confirm NimBLE version is 1.9.0 or newer in build metadata
- Verify existing bonds are not overwritten by unsolicited re-bonding attempts
- Test pairing behavior under normal and abnormal conditions
- Confirm malformed HCI packets are rejected and logged
- Ensure debug and HCI interfaces are locked down in production firmware
