CVE-2026-98482: nfc: llcp: drop truncated I/RR/RNR PDUs in nfc_llcp_recv_hdlc()
In the Linux kernel, the following vulnerability has been resolved:
nfc: llcp: drop truncated I/RR/RNR PDUs in nfcllcprecvhdlc()
nfcllcprecvhdlc() reads the sequence byte skb->data[2], via nfcllcpns()/nfcllcpnr(), before any length check. The receive path only guarantees the two-byte LLCP header -- nfcllcprecv() checks it with pskbmaypull() and nfcllcprecvagf() admits two-byte inner PDUs -- so a two-byte I, RR or RNR PDU reads one byte of uninitialised skb tailroom. The byte becomes N(R)/N(S); a peer can already set those with a well-formed PDU, so this is acting on uninitialised memory, not new peer control.
Guard the read with pskbmaypull(), as commit 95674f506c63 ("nfc: llcp: reject PDUs shorter than the LLCP header") did for the two-byte header, so the sequence byte is present and linear before it is read. RR and RNR PDUs are LLCPHEADERSIZE + LLCPSEQUENCESIZE bytes and an I PDU is longer, so no valid frame is rejected; a truncated PDU is malformed, so return without a DM reply.
Affected Software
Remediation
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Fixed in 6.6.159.1-1 - Upgrade
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In nfc_llcp_recv_hdlc(), guard access to skb->data[2] with pskb_may_pull() so the sequence byte is present and linear; drop truncated I, RR, and RNR PDUs without sending a DM reply.
Event History
Frequently Asked Questions
What must an attacker be able to do to reach the vulnerable path?
An attacker needs to send a malformed, truncated LLCP I, RR, or RNR PDU to the affected NFC LLCP receive path. The malformed frame contains only the two-byte LLCP header, causing the kernel to read a missing sequence byte from uninitialised skb tailroom.
Are valid LLCP frames affected by the fix?
No. RR and RNR PDUs normally include both the LLCP header and sequence byte, and I PDUs are longer; the added length check rejects only truncated malformed PDUs.
What behavior indicates the system has the remediation?
The receive handler checks that the sequence byte is present and linear with pskb_may_pull() before calling nfc_llcp_ns() or nfc_llcp_nr(). Truncated I, RR, and RNR PDUs are dropped without sending a DM reply.