CVE-2026-80823 in Linux
Summary
by MITRE • 09/04/2026
In the Linux kernel, the following vulnerability has been resolved:
nfc: st21nfca: validate ATR_REQ length against the received frame
st21nfca_tm_recv_atr_req() checks that the received ATR_REQ frame is at least ST21NFCA_ATR_REQ_MIN_SIZE and that the self-declared atr_req->length is at least sizeof(struct st21nfca_atr_req), but never checks that atr_req->length does not exceed the actual received length (skb->len).
st21nfca_tm_send_atr_res() then trusts the declared length:
gb_len = atr_req->length - sizeof(struct st21nfca_atr_req); ... memcpy(atr_res->gbi, atr_req->gbi, gb_len);
so an RF peer that sends a short frame but sets atr_req->length larger than the frame makes gb_len exceed the general bytes actually present, and the memcpy reads out of bounds past the received skb. Those bytes are placed in the ATR_RES and sent back to the peer (kernel-memory disclosure to a proximity attacker); a larger declared length is an out-of-bounds read (DoS).
Reject frames whose declared length exceeds the received length. The adjacent nfc_tm_activated() path in the same function already derives its general-bytes length from skb->len rather than the declared field.
Found by 0sec (https://0sec.ai) using automated source analysis; the missing bound is evident from source. Compile-tested.
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Analysis
by VulDB Data Team • 09/04/2026
The vulnerability identified within the Linux kernel's Near Field Communication subsystem specifically affects the st21nfca driver, which handles communication with STMicroelectronics NFC controllers. This flaw represents a critical failure in input validation during the processing of Answer to Reset (ATR) requests received from RF peers. The core technical issue lies in the function st21nfca_tm_recv_atr_req(), where the kernel performs basic sanity checks on incoming frames but fails to enforce upper bounds on data length fields provided by external entities. While the code verifies that a received ATR_REQ frame meets a minimum size requirement and ensures the self-declared atr_req->length is at least large enough to contain the expected structure, it completely neglects to verify whether this declared length exceeds the actual amount of data present in the socket buffer skb->len. This omission creates a significant discrepancy between trusted metadata provided by an attacker-controlled source and the physical limits of available memory buffers.
The operational impact of this vulnerability is severe due to how subsequent functions handle the unvalidated length field. The function st21nfca_tm_send_atr_res() relies directly on atr_req->length to calculate gb_len, which determines the number of bytes copied into the response frame using memcpy. When an RF peer transmits a short frame but artificially inflates the atr_req->length value beyond the actual received data size, gb_len becomes larger than the available buffer contents. Consequently, the kernel performs an out-of-bounds read, accessing memory locations immediately following the original skb allocation. This behavior results in two distinct security consequences depending on the magnitude of the length mismatch and system state. First, it leads to a kernel-memory disclosure vulnerability where sensitive data from adjacent kernel memory regions is inadvertently included in the ATR_RES response sent back to the proximity attacker. Second, if the declared length is excessively large or points to unmapped pages, it can trigger a fault condition leading to a Denial of Service by crashing the affected system component or potentially destabilizing the entire kernel.
This vulnerability aligns with Common Weakness Enumeration CWE-125 Out-of-bounds Read and CWE-20 Improper Input Validation. From an adversarial perspective, this flaw facilitates exploitation via the ATT&CK technique T1608 Link Exploitation, as it allows a nearby attacker to interact directly with the NFC interface without physical access or complex network positioning. The attack vector is local but requires proximity due to the nature of Near Field Communication protocols, making it particularly relevant for mobile devices and embedded systems where NFC interfaces are commonly exposed. The lack of boundary checking on untrusted input length fields is a classic pattern that undermines memory safety guarantees in C-based kernel drivers.
To mitigate this vulnerability, developers must implement strict validation logic within st21nfca_tm_recv_atr_req() to ensure that atr_req->length does not exceed the actual received frame size stored in skb->len. The fix involves adding a conditional check that rejects any ATR_REQ frames where the declared length is greater than the available buffer data, thereby preventing the downstream memcpy operation from reading beyond allocated memory boundaries. This approach mirrors existing safe practices within the same driver module, such as those found in nfc_tm_activated(), which correctly derive general-bytes lengths directly from skb->len rather than trusting external declarations. System administrators should ensure that kernel updates incorporating this patch are applied promptly to close the information disclosure and denial-of-service vectors exposed by NFC-enabled devices.