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CVE-2026-80819 Affecting linux-6.12 package, versions <6.12.107-1~deb12u1

Severity

 Recommended
low

Based on default assessment until relevant scores are available.

Threat Intelligence

EPSS
0.2% (10th percentile)

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  • Snyk IDSNYK-ECHOLATEST-LINUX612-19964491
  • published20 Sept 2026
  • disclosed4 Sept 2026
Report a new vulnerability Found a mistake?

Introduced: 4 Sep 2026

NewCVE-2026-80819  (opens in a new tab)

How to fix?

Upgrade Echo:latest linux-6.12 to version 6.12.107-1~deb12u1 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream linux-6.12 package and not the linux-6.12 package as distributed by Echo. See How to fix? for Echo:latest relevant fixed versions and status.

In the Linux kernel, the following vulnerability has been resolved:

Bluetooth: RFCOMM: take rfcomm_mutex for the deferred setup accept

rfcomm_sock_recvmsg() completes a deferred setup by calling rfcomm_dlc_accept() without holding any RFCOMM lock:

if (test_and_clear_bit(RFCOMM_DEFER_SETUP, &amp;d-&gt;flags)) {
    rfcomm_dlc_accept(d);
    return 0;
}

and rfcomm_dlc_accept() dereferences the session on its first line:

struct sock *sk = d-&gt;session-&gt;sock-&gt;sk;

Every other path that touches d->session runs under rfcomm_mutex: rfcomm_dlc_open(), rfcomm_dlc_close(), rfcomm_dlc_exists(), rfcomm_dlc_send_rpn(), and the RFCOMM thread through rfcomm_process_sessions(). rfcomm_connect_ind() is even documented as "called under rfcomm_lock()". This call site is the only one that skips it.

The RFCOMM_DEFER_SETUP bit looks like it serialises the accept against teardown, since __rfcomm_dlc_close() returns early when it wins the test_and_clear. But rfcomm_recv_disc() forces the state first:

d-&gt;state = BT_CLOSED;
__rfcomm_dlc_close(d, err);

and the early return only covers BT_CONNECT, BT_CONFIG, BT_OPEN and BT_CONNECT2. With the state already BT_CLOSED that switch does not match, the bit is never consulted, and __rfcomm_dlc_close() falls through to rfcomm_dlc_unlink(), which sets d->session = NULL.

So a remote DISC on a deferred dlc clears the session while leaving RFCOMM_DEFER_SETUP set. The next recvmsg() then passes the test_and_clear and dereferences a NULL session. No timing window is needed: once the DISC has been processed, the dereference is unconditional.

Give rfcomm_dlc_accept() the same shape as rfcomm_dlc_open() and rfcomm_dlc_close(): an exported wrapper that takes rfcomm_mutex and re-checks the session, around a __rfcomm_dlc_accept() that the two in-core callers, which already hold the mutex, keep using.

Reproduced on a KASAN + PROVE_LOCKING kernel with a BR/EDR peer emulated over /dev/vhci: the peer brings up an ACL link, opens L2CAP on the RFCOMM PSM, starts a session, opens a dlc on a channel bound with BT_DEFER_SETUP, and sends DISC after the socket is accepted. recv() on the accepted socket then hits:

Oops: general protection fault KASAN: null-ptr-deref in range [0x0000000000000010-0x0000000000000017] RIP: 0010:rfcomm_dlc_accept+0x54/0x350 Call Trace: rfcomm_sock_recvmsg+0x1cd/0x230 sock_recvmsg+0x166/0x1c0 __sys_recvfrom+0x20d/0x300

0x10 is the offset of sock in struct rfcomm_session. With this patch the same run completes with recv() returning 0 and no report, and lockdep stays quiet, confirming rfcomm_mutex is still taken before lock_sock on this path as it is on the thread side.