CVE-2017-1000410

What it actually does

Uninitialized stack variable in l2cap_parse_conf_req and l2cap_parse_conf_rsp can be returned to a remote peer when an L2CAP_CONF_EFS element with mismatched length is supplied, leaking up to 16 bytes that may contain kernel pointers or stack canaries.

Why it matters to the business

Attackers gain an information-disclosure primitive that weakens kernel exploit mitigations on any system exposing Bluetooth L2CAP, raising the likelihood of successful remote kernel compromise and subsequent data theft or persistence.

How an attack unfolds

An attacker establishes an L2CAP connection, sends a ConfigRequest or ConfigResponse containing an EFS element whose length field does not equal sizeof(struct l2cap_conf_efs), skips the memcpy, then receives the uninitialized efs structure in the subsequent configuration packet; the leaked bytes are used to defeat KASLR or stack canaries, after which the attacker chains the disclosure with a separate L2CAP RCE such as CVE-2017-1000251.

How to fix it

Upgrade the Linux kernel to the commit d8a5b80568a9cb66810e75b182018e9edb68e8ff or any later mainline or distribution release that contains the fix; disable Bluetooth if the interface is not required.

How to confirm the fix worked

Verify the running kernel contains commit d8a5b80568a9cb66810e75b182018e9edb68e8ff; confirm the l2cap_parse_conf_req and l2cap_parse_conf_rsp functions now initialize the efs structure before l2cap_add_conf_opt.

Typical attack path

1. Establish Bluetooth L2CAP channel to target
2. Transmit ConfigRequest/Response with L2CAP_CONF_EFS element of incorrect olen
3. Receive response containing uninitialized stack bytes
4. Parse leaked pointers or canaries to prepare follow-on exploit
5. Deliver chained payload that bypasses mitigations and achieves RCE

How to detect it

Inspect Bluetooth host-controller logs and packet captures for L2CAP configuration packets carrying EFS elements whose length field deviates from the expected 16-byte structure; correlate with kernel stack traces or Oops messages indicating information disclosure.

What your security team should do

• Apply the referenced kernel commit or equivalent distribution update on all systems exposing Bluetooth
• Disable the Bluetooth stack via kernel configuration or runtime module blacklisting where Bluetooth is unnecessary
• Add network monitoring for anomalous L2CAP configuration traffic on Bluetooth interfaces