What’s Vulnerable › Vulnerabilities

CVE-2025-39889: Bluetooth: l2cap: Check encryption key size on incoming connection

• Severity: medium (CVSS 5.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.1% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-09-24 · updated 2026-09-26
• Weakness: CWE-326

Description

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)

Affected products

• Linux kernel: from 5.11 before 5.15.181; from 5.16 before 6.1.135; from 6.2 before 6.6.88; from 6.7 before 6.12.25; from 6.13 before 6.14.4; 6.15-rc1, 6.15-rc2 — fixed in 5.15.181, 6.1.135, 6.12.25, 6.14.4, 6.6.88

How to fix

Upgrade to a fixed version: Linux kernel 5.15.181, 6.1.135, 6.12.25, 6.14.4. Check the vendor advisory for mitigations.

References

• https://git.kernel.org/stable/c/24b2cdfc16e9bd6ab3d03b8e01c590755bd3141f
• https://git.kernel.org/stable/c/522e9ed157e3c21b4dd623c79967f72c21e45b78
• https://git.kernel.org/stable/c/9e3114958d87ea88383cbbf38c89e04b8ea1bce5
• https://git.kernel.org/stable/c/c6d527bbd3d3896375079f5dbc8b7f96734a3ba5
• https://git.kernel.org/stable/c/d49798ecd26e0ee7995a7fc1e90ca5cd9b4402d6
• https://git.kernel.org/stable/c/d4ca2fd218caafbf50e3343ba1260c6a23b5676a
• https://git.kernel.org/stable/c/ed503d340a501e414114ddc614a3aae4f6e9eae2

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