CVE-2026-80802 in Linux
Summary
by MITRE • 09/04/2026
In the Linux kernel, the following vulnerability has been resolved:
nfc: fdp: bound the device-reported read length and fix an skb leak
fdp_nci_i2c_read() takes the next packet length from two device-supplied bytes and never validates it. The value is a u16 used as the i2c_master_recv() count into a 261-byte on-stack buffer: a malicious, counterfeit or malfunctioning controller (or an i2c bus interposer) can drive it far past the buffer for a stack out-of-bounds write that clobbers the canary and return address, or below the minimum frame size (directly, or by truncating the computed sum) so the header/LRC strip and the next length read run past a short receive. Reject a length outside [FDP_NCI_I2C_MIN_PAYLOAD, FDP_NCI_I2C_MAX_PAYLOAD], as a
corrupted packet already is, and force resynchronization.
The same loop allocates one data skb per iteration and assumes a length packet followed by a data packet; a device that sends two data packets in one call leaks the first skb when the second allocation overwrites it. Free a previously allocated skb before allocating the next.
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Analysis
by VulDB Data Team • 09/04/2026
The vulnerability identified within the Linux kernel's Near Field Communication (NFC) subsystem, specifically affecting the fdp_nci_i2c_read function, represents a critical failure in input validation and resource management for I2C-connected NFC controllers. This flaw allows for both stack-based buffer overflows and memory leaks that can be exploited by malicious or malfunctioning hardware devices connected via the Inter-Integrated Circuit bus. The core of the issue lies in how the driver processes packet lengths provided directly by the device without any sanity checks against expected operational boundaries. By accepting a u16 value representing the next packet length from two untrusted bytes, the code proceeds to use this value as the count for i2c_master_recv operations targeting a fixed-size on-stack buffer of 261 bytes. This lack of validation creates a direct pathway for stack out-of-bounds writes if an attacker controls or spoofs the device connected to the I2C bus.
From a technical perspective, the absence of bounds checking permits a malicious controller, such as one that is counterfeit or physically compromised by an interposer on the I2C line, to supply length values significantly exceeding the buffer capacity. When i2c_master_recv attempts to read this excessive amount of data into the stack-allocated space, it overwrites adjacent memory locations, including the stack canary and return addresses. This condition aligns with CWE-120 Buffer Copy without Checking Size of Input Classic Buffer Overflow, enabling potential arbitrary code execution or denial of service through kernel panic if the overwritten control flow leads to an invalid instruction pointer. Furthermore, the vulnerability extends beyond simple overflow; by providing a length below the minimum frame size, either directly or via truncation of computed sums, the driver may fail to correctly strip headers and Link Control Responses (LRC). This misalignment causes subsequent reads to operate on incorrect offsets, further exacerbating memory corruption risks and protocol desynchronization.
In addition to the buffer overflow risk, the implementation contains a significant resource management flaw leading to kernel memory leaks. The processing loop allocates one socket buffer skb per iteration under the assumption that each call will receive exactly one length packet followed by one data packet. However, if a device sends two consecutive data packets within a single invocation, the driver fails to release the first allocated skb before allocating space for the second. This results in the loss of reference to the initial memory block, causing it to remain allocated but unreachable until system reboot or extreme resource exhaustion. This scenario corresponds closely with CWE-401 Missing Release of Memory after Effective Lifetime and CWE-772 Missing Release of Resource after Effective Lifetime, contributing to gradual degradation of system stability over time as kernel heap space is consumed by orphaned buffers.
The operational impact of these vulnerabilities is severe for systems relying on NFC connectivity, particularly in environments where hardware trust boundaries are not strictly enforced or where devices may be physically accessible to adversaries. An attacker with physical access could exploit the stack overflow to escalate privileges from user space to ring zero kernel level, gaining full control over the host system. Alternatively, they could trigger a denial of service by crashing the kernel through corrupted return addresses or exhausting memory resources via repeated allocation without deallocation. These risks are particularly pertinent in IoT and mobile device ecosystems where NFC interfaces are common entry points for physical attacks. The vulnerability is categorized under MITRE ATT&CK techniques related to exploitation of remote services and local privilege escalation, specifically leveraging improper input validation to bypass security controls.
To mitigate these issues, the Linux kernel maintainers have implemented strict bounds checking on the device-reported read length. The fix enforces that any received packet length must fall within defined operational limits, specifically between FDP_NCI_I2C_MIN_PAYLOAD and FDP_NCI_I2C_MAX_PAYLOAD values. By rejecting packets with lengths outside this range, the driver prevents both stack overflows caused by excessive data reads and protocol errors resulting from undersized frames. Additionally, the logic has been updated to ensure proper resource cleanup; a previously allocated skb is now freed before allocating memory for subsequent packets within the same loop iteration. This change ensures that no socket buffers are leaked during multi-packet exchanges, maintaining kernel heap integrity. System administrators should apply these kernel updates immediately and consider physical security measures to prevent unauthorized access to NFC controller interfaces, as software mitigations alone cannot fully protect against hardware-level tampering or sophisticated interposer attacks on the I2C bus.