CVE-2025-52435: 
NixOS vulnerability analysis and mitigation

CVE-2025-52435 is a data transmission without encryption vulnerability in Apache NimBLE (the Bluetooth Low Energy stack for Apache Mynewt) affecting all versions through 1.8.0. The flaw involves improper handling of the Pause Encryption procedure at the BLE Link Layer, which can leave a previously encrypted connection in an unencrypted state, allowing a nearby eavesdropper to observe the remainder of the communication exchange. It was reported by Henrik Schnor, disclosed via the oss-security mailing list on January 8, 2026, and published as a CVE on January 10, 2026. The vulnerability carries a CVSS v3.1 base score of 7.5 (High) (Openwall OSS-Sec, Apache Advisory).

The root cause is classified as CWE-5 (J2EE Misconfiguration: Data Transmission Without Encryption), reflecting improper state management during the BLE Pause Encryption procedure. Specifically, the NimBLE Link Layer controller failed to restrict which LL Control PDUs were permitted in each encryption state, and did not correctly handle the case where a host provides a negative LTK reply following a Pause Encryption sequence — leaving the connection in an unencrypted (CONN_ENC_S_PAUSED) state rather than terminating it. The fix introduced state-aware PDU filtering in ble_ll_ctrl_enc_allowed_pdu_rx() and added an encrypt_paused flag to ensure that when the host fails to provide an LTK after a Pause Encryption procedure, the link is terminated with error code PIN or Key Missing (0x06) per Bluetooth Core Spec 6.1, Vol 6, Part B, §5.1.3.1 (GitHub Commit 1, GitHub Commit 2).

Successful exploitation allows a passive eavesdropper within Bluetooth radio range to observe plaintext BLE traffic that was previously protected by encryption. The confidentiality impact is high — any sensitive data exchanged after the encryption pause (e.g., sensor readings, authentication tokens, health data) is exposed. Integrity and availability are not directly affected by this vulnerability. The scope is limited to the affected BLE connection, but in IoT and embedded deployments using Apache Mynewt NimBLE, this could expose sensitive application-layer data (Openwall OSS-Sec, Apache Advisory).

1. Reconnaissance: Identify target devices running Apache NimBLE versions ≤ 1.8.0 using BLE scanning tools (e.g., hcitool lescan, Wireshark with a BLE sniffer, or a dedicated BLE analyzer like Ubertooth One).
2. Position for passive capture: Place a BLE sniffer within radio range of the target device to capture all Link Layer PDUs on the active BLE connection.
3. Trigger Pause Encryption procedure: Act as or wait for the central device to initiate a LL_PAUSE_ENC_REQ procedure (e.g., during re-keying or connection parameter updates). This causes the NimBLE peripheral to transition to the paused encryption state.
4. Observe unencrypted traffic: Due to the improper state handling, the connection remains in an unencrypted state after the pause procedure completes. The sniffer captures subsequent plaintext PDUs that should have been re-encrypted.
5. Extract sensitive data: Analyze the captured plaintext BLE traffic for application-layer data such as sensor readings, credentials, or other sensitive information (Openwall OSS-Sec, GitHub Commit 1).

• Network/RF: Unexpected unencrypted BLE PDUs observed on a connection that was previously encrypted, detectable via BLE protocol analyzers (e.g., Wireshark, Ubertooth); BLE Link Layer PDUs with LLID indicating data frames transmitted without encryption after a LL_PAUSE_ENC_REQ/LL_PAUSE_ENC_RSP exchange.
• Logs: On NimBLE-based devices with debug logging enabled, absence of re-encryption confirmation (CONN_ENC_S_ENCRYPTED state) following a Pause Encryption sequence; unexpected connection termination events with error code BLE_ERR_CONN_TERM_MIC (0x3D) if the patched version is deployed and detects the anomaly.
• Device Behavior: Devices running NimBLE ≤ 1.8.0 that do not terminate the BLE link after a failed LTK reply following a Pause Encryption procedure may indicate exploitation conditions.

The Apache Software Foundation has released NimBLE version 1.9.0, which fixes this vulnerability via two commits: one restricting allowed LL Control PDUs per encryption state, and another ensuring the link is terminated when the host provides a negative LTK reply after a Pause Encryption procedure. All users of Apache NimBLE ≤ 1.8.0 are strongly recommended to upgrade to version 1.9.0 immediately. No configuration-based workaround is available; upgrading is the only remediation (Apache Advisory, GitHub Commit 1, GitHub Commit 2).

The vulnerability was covered by security news outlet SecurityOnline.info under the headline "Bluetooth Broken: Apache NimBLE Flaws Enable Spoofing, Eavesdropping," indicating moderate community interest. Social media activity was observed on Bluesky and Mastodon, primarily from automated CVE tracking accounts. The Apache Software Foundation credited researcher Henrik Schnor for the responsible disclosure. No major vendor statements beyond the Apache advisory have been identified (Openwall OSS-Sec).