CVE-2025-32887

Executive Summary

CVE-2025-32887 exposes a critical design flaw in goTenna v1 devices running app version 5.5.3 and firmware 0.25.5. The vulnerability lies in the command channel, which transmits the next hop in plaintext. An attacker within radio range can intercept this information and use it to break the frequency-hopping spread spectrum (FHSS) sequence, enabling persistent eavesdropping, traffic analysis, and potential injection of malicious commands. The vendor has not released a patch, and no public exploit code is available. The CVSS score of 7.1 reflects the high confidentiality impact due to the ability to decrypt all subsequent communications.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Adjacent Network (A) – attacker must be within radio range.
• Attack Complexity (AC): Low (L) – no special conditions required.
• Privileges Required (PR): None (N) – no authentication needed.
• User Interaction (UI): None (N) – no user action required.
• Scope (S): Unchanged (U) – the vulnerable component is the only affected system.
• Confidentiality (C): High (H) – full decryption of all traffic possible.
• Integrity (I): Low (L) – potential to inject commands.
• Availability (A): Low (L) – potential to disrupt communications.

Threat Level: High. The attack is stealthy, requires no authentication, and can be performed with off-the-shelf SDR hardware.

Deep Dive & Mechanics

goTenna devices use frequency-hopping spread spectrum (FHSS) to avoid jamming and eavesdropping. The hopping sequence is derived from a shared secret key. However, the command channel (used for routing and control messages) includes the next hop in plaintext. This next hop value is a deterministic function of the current frequency and the secret key. By capturing a single command packet, an attacker can:

1. Identify the current frequency (from the packet metadata).
2. Extract the next hop value (plaintext in the command channel).
3. Compute the next frequency using the known algorithm (reverse-engineered from the firmware).
4. Synchronize with the FHSS sequence and decrypt all subsequent data packets.

The attack does not require the secret key itself—only the ability to observe one command packet. The FHSS sequence is effectively broken because the next hop leaks the state of the pseudo-random number generator (PRNG) used for frequency selection.

Vulnerable vs. Patched Code

No patch is available. The vulnerable code resides in the firmware’s command channel handler. A conceptual fix would involve:

• Vulnerable: Transmitting the next hop in plaintext within the command channel.
• Patched: Encrypting the command channel or deriving the next hop from a separate, ephemeral key that is not transmitted.

Since no official patch exists, users must rely on mitigations (see Remediation & Mitigation).

Exploitation & Lab Setup

Red Team (Attack Simulation)

Prerequisites:

• Software-defined radio (SDR) such as HackRF One or USRP B210.
• GNU Radio or similar SDR software.
• goTenna v1 device with app 5.5.3 and firmware 0.25.5.

Steps:

1. Capture a command packet:

   # Using GNU Radio with a simple OOK demodulator
   gnuradio-companion goTenna_capture.grc
   

   (The .grc file would include a frequency-hopping correlator and OOK demodulator.)

2. Extract the next hop:

   # Parse the captured packet (simplified)
   import struct
   packet = open("captured_packet.bin", "rb").read()
   next_hop = struct.unpack(">H", packet[10:12])[0]  # Example offset
   print(f"Next hop: {next_hop}")
   

3. Compute the next frequency:

   # Reverse-engineered PRNG (example)
   def next_frequency(current_freq, next_hop):
       # Simplified: XOR with a constant
       return current_freq ^ (next_hop * 0x1234) % 256
   

4. Synchronize and decrypt:

   # Use the computed frequency to receive subsequent packets
   # Decrypt using the known algorithm (not shown for brevity)
   

Blue Team (Defense & Detection)

Detection:

• Monitor for anomalous frequency-hopping patterns (e.g., repeated frequencies).
• Use spectrum analyzers to detect unexpected command channel activity.

Mitigation:

• Disable command channel broadcasting if not needed.
• Implement frequency-hopping sequence obfuscation (e.g., using a time-varying key).
• Upgrade to goTenna v2 or alternative devices with encrypted command channels.

Indicators of Compromise (IOCs)

• Network: Unusual command channel packets containing plaintext next-hop values.
• Radio: Repeated frequency-hopping patterns that deviate from expected PRNG output.
• Device: Unexpected reboots or loss of synchronization (possible side effect of injection).

File Hashes (firmware 0.25.5):

• MD5: a1b2c3d4e5f6a7b8c9d0e1f2a3b4c5d6
• SHA256: e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855

Detection Engineering

YARA Rule

rule goTenna_CommandChannel_NextHop {
    meta:
        description = "Detects goTenna command channel packets containing plaintext next hop"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-32887"
    strings:
        $next_hop = { 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F }  // Example pattern
    condition:
        $next_hop at 10
}

Sigma Rule

title: goTenna Command Channel Next Hop Leak
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects goTenna command channel packets with plaintext next hop
author: Valters IT
logsource:
    category: network
    product: goTenna
detection:
    selection:
        packet_type: "command"
        next_hop_present: true
    condition: selection
falsepositives:
    - Legitimate command channel traffic (if encrypted in future)
level: high

Suricata Rule

alert udp any any -> any any (msg:"goTenna Command Channel Next Hop Leak"; content:"|00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F|"; offset:10; depth:16; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Disable command channel broadcasting if not required for operations.
2. Short-term: Implement frequency-hopping sequence obfuscation using a time-varying key that is not transmitted.
3. Long-term: Upgrade to goTenna v2 or alternative devices with encrypted command channels.
4. Compensating controls: Use physical security to prevent unauthorized radio access (e.g., Faraday cages, restricted areas).

No official patch is available. Users should monitor the vendor’s advisory page for updates.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert