CVE-2026-80800: nfc: llcp: bound the connect_sn TLV walk to the skb
In the Linux kernel, the following vulnerability has been resolved:
nfc: llcp: bound the connectsn TLV walk to the skb
Commit 27256cdb290e ("nfc: llcp: bound SNL TLV parsing to the skb and add length checks") fixed the unbounded TLV walk in nfcllcprecvsnl(), and commit d8bd2dedbde5 ("nfc: llcp: fix OOB read and u8 offset wrap in TLV parsers") subsequently bounded nfcllcpparsegbtlv() and nfcllcpparseconnectiontlv(). One sibling parser sharing the same pattern remains unbounded: nfcllcpconnectsn().
nfcllcpconnectsn() walks a TLV list, reading a two-byte header (type, length) followed by length bytes of value, without checking that the two header bytes or the declared length stay within the buffer. It returns a pointer to a service name of up to 255 bytes that may point past the end of the skb; it is subsequently consumed by memcmp() in nfcllcpsockfromsn(). In addition tlvarraylen was computed as "skb->len - LLCPHEADERSIZE" in sizet, so a CONNECT/CC frame shorter than the LLCP header underflows to a huge length and the walk runs far past the buffer.
nfcllcpconnectsn() is reachable from nfcllcprecvconnect() and nfcllcprecvcc(), i.e. from received CONNECT and CC PDUs. A nearby NFC device can reach this without authentication; LLCP link activation happens automatically after NFC-DEP, and the nfcllcprxskb() dispatcher applies no minimum-length guard.
Walk the TLV list by pointer, bounded by skbtailpointer(skb), and validate each declared length before use, matching the approach already used for nfcllcprecvsnl(). Starting the walk at &skb->data[LLCPHEADERSIZE] against the tail pointer also removes the sizet underflow for short frames.
Found by 0sec automated security-research tooling (https://0sec.ai).
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
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Modify nfc_llcp_connect_sn() to walk the TLV list by pointer, bound the walk by skb_tail_pointer(skb), validate that each two-byte TLV header and its declared length remain within the skb before use, and prevent processing frames shorter than LLCP_HEADER_SIZE.
Event History
Frequently Asked Questions
What access would an attacker need to reach the vulnerable code?
An attacker would need to send crafted NFC LLCP CONNECT or CC frames to a system that processes received LLCP traffic. The affected parser is reached through the CONNECT and CC receive paths.
What malformed input conditions trigger the out-of-bounds parsing?
A frame shorter than the LLCP header can cause the computed TLV length to underflow, making the parser walk far beyond the skb buffer. TLVs with incomplete two-byte headers or declared value lengths extending past the buffer can also lead to reads beyond the received data.