CVE-2026-53208
MediumCVSS 5.5Exploitation Probability (EPSS)
Low risk2th percentile - higher than 2% of all known CVEs
Summary
In the Linux kernel's Bluetooth L2CAP subsystem, a vulnerability allows an unauthenticated BR/EDR peer within radio range to send a signaling packet larger than the allowed MTU (MTUsig). Such a packet can contain multiple ECHO_REQ commands, forcing the target device to send many ECHO_RSP responses, potentially leading to overload.
Risk Assessment
An attacker before pairing can send a single packet (e.g., 681 bytes) containing 168 ECHO_REQ commands, causing 168 ECHO_RSP responses to be sent within about 220 ms. This can lead to excessive bandwidth consumption and potential denial of service (DoS) for the target device.
Recommendation
Immediately update the Linux kernel to a version containing the fix, which defines the BR/EDR signaling MTU as 48 bytes (per specification) and rejects larger signaling packets with L2CAP_COMMAND_REJECT_RSP.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: Bluetooth: L2CAP: reject BR/EDR signaling packets over MTUsig net/bluetooth/l2cap_core.c:l2cap_sig_channel() accepts BR/EDR signaling packets up to the channel MTU and dispatches each command without enforcing the signaling MTU (MTUsig). A Bluetooth BR/EDR peer within radio range can send a fixed-channel CID 0x0001 packet that is larger than MTUsig and contains many L2CAP_ECHO_REQ commands before pairing. In a real-radio stock-kernel run, one 681-byte signaling packet containing 168 zero-length ECHO_REQ commands made the target transmit 168 ECHO_RSP frames over about 220 ms. Impact: a Bluetooth BR/EDR peer within radio range, before pairing, can force 168 ECHO_RSP frames from one 681-byte fixed-channel signaling packet containing packed ECHO_REQ commands. Define Linux's BR/EDR signaling MTU as the spec minimum of 48 bytes and reject any larger signaling packet with one L2CAP_COMMAND_REJECT_RSP carrying L2CAP_REJ_MTU_EXCEEDED before any command is dispatched. The Bluetooth Core spec wording for MTUExceeded says the reject identifier shall match the first request command in the packet, and that packets containing only responses shall be silently discarded. Linux intentionally deviates from that prescription: silently discarding desynchronizes the peer because the remote stack never learns its responses were dropped, and locating the first request command requires walking command headers past MTUsig, i.e. processing bytes from a packet we have already decided is too large to process. We therefore always emit one reject and use the identifier from the first command header, a single fixed-offset byte read. The unrestricted BR/EDR signaling parser and ECHO_REQ response path both trace to the initial git import; no later introducing commit is available for a Fixes tag.