CVE-2025-39889
Description
From CVE.org
In the Linux kernel, the following vulnerability has been resolved: Bluetooth: l2cap: Check encryption key size on incoming connection This is required for passing GAP/SEC/SEM/BI-04-C PTS test case: Security Mode 4 Level 4, Responder - Invalid Encryption Key Size - 128 bit This tests the security key with size from 1 to 15 bytes while the Security Mode 4 Level 4 requests 16 bytes key size. Currently PTS fails with the following logs: - expected:Connection Response: Code: [3 (0x03)] Code Identifier: (lt)WildCard: Exists(gt) Length: [8 (0x0008)] Destination CID: (lt)WildCard: Exists(gt) Source CID: [64 (0x0040)] Result: [3 (0x0003)] Connection refused - Security block Status: (lt)WildCard: Exists(gt), but received:Connection Response: Code: [3 (0x03)] Code Identifier: [1 (0x01)] Length: [8 (0x0008)] Destination CID: [64 (0x0040)] Source CID: [64 (0x0040)] Result: [0 (0x0000)] Connection Successful Status: [0 (0x0000)] No further information available And HCI logs: < HCI Command: Read Encrypti.. (0x05|0x0008) plen 2 Handle: 14 Address: 00:1B:DC:F2:24:10 (Vencer Co., Ltd.) > HCI Event: Command Complete (0x0e) plen 7 Read Encryption Key Size (0x05|0x0008) ncmd 1 Status: Success (0x00) Handle: 14 Address: 00:1B:DC:F2:24:10 (Vencer Co., Ltd.) Key size: 7 > ACL Data RX: Handle 14 flags 0x02 dlen 12 L2CAP: Connection Request (0x02) ident 1 len 4 PSM: 4097 (0x1001) Source CID: 64 < ACL Data TX: Handle 14 flags 0x00 dlen 16 L2CAP: Connection Response (0x03) ident 1 len 8 Destination CID: 64 Source CID: 64 Result: Connection successful (0x0000) Status: No further information available (0x0000)
Statement
The Bluetooth L2CAP stack accepted incoming connections even when the negotiated BR/EDR encryption key size was below the policy requirement (e.g., <16 bytes for Security Mode 4 Level 4), effectively allowing a downgrade to weaker encryption. The fix adds an explicit key-size check for non-SDP PSMs and rejects such connections with SECURITY BLOCK. Practically, a nearby device could trigger this only over an established encrypted link with a too-short key, resulting in policy bypass and weaker protection rather than a kernel crash.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.4 | 5.5 | 8.1 |
| Attack Vector | Adjacent Network | Local | Adjacent Network |
| Attack Complexity | Low | Low | Low |
| Privileges Required | None | Low | None |
| User Interaction | None | None | None |
| Scope | Unchanged | Unchanged | Unchanged |
| Confidentiality | Low | None | High |
| Integrity Impact | Low | None | High |
| Availability Impact | None | High | None |
Vector
Red Hat: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
NVD: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
cve.org: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Understanding the Weakness (CWE)
Access Control,Confidentiality
Technical Impact: Bypass Protection Mechanism; Read Application Data
An attacker may be able to decrypt the data using brute force attacks.
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