CVE-2026-31622 — NFC: digital: Bounds check NFC-A cascade depth in SDD response handler

Affected: Linux

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

NFC: digital: Bounds check NFC-A cascade depth in SDD response handler

The NFC-A anti-collision cascade in digital_in_recv_sdd_res() appends 3 or 4 bytes to target->nfcid1 on each round, but the number of cascade rounds is controlled entirely by the peer device. The peer sets the cascade tag in the SDD_RES (deciding 3 vs 4 bytes) and the cascade-incomplete bit in the SEL_RES (deciding whether another round follows).

ISO 14443-3 limits NFC-A to three cascade levels and target->nfcid1 is sized accordingly (NFC_NFCID1_MAXSIZE = 10), but nothing in the driver actually enforces this. This means a malicious peer can keep the cascade running, writing past the heap-allocated nfc_target with each round.

Fix this by rejecting the response when the accumulated UID would exceed the buffer.

Commit e329e71013c9 ("NFC: nci: Bounds check struct nfc_target arrays") fixed similar missing checks against the same field on the NCI path.

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CVE-2026-31622 — NFC: digital: Bounds check NFC-A cascade depth in SDD response handler