CVE-2026-102721

A TFTP server that answers with a short ERROR packet makes the client read up to 64 bytes past the

received datagram.

Each receive path checks only that the datagram is at least four bytes long (nxd_tftp_client.c:1229,

1521, 1984). When the opcode is NX_TFTP_CODE_ERROR the message string is copied with a loop whose

only limits are the destination buffer and a NUL byte:

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/* addons/tftp/nxd_tftp_client.c:1769 */



for (i = 0; (i < (sizeof(tftp_client_ptr -> nx_tftp_client_error_string) - 1)) && (*buffer_ptr); i++)

Nothing compares buffer_ptr against nx_packet_append_ptr. An ERROR packet that carries no

terminating NUL, which a server controls completely, walks the loop off the end of the packet until

it happens to meet a zero byte or fills the 64 byte destination.

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ERROR: AddressSanitizer: heap-buffer-overflow



READ of size 1 at 0x60d0000000c8 thread T4

    #0 _nxd_tftp_client_file_read  addons/tftp/nxd_tftp_client.c:1769


0x60d0000000c8 is 0 bytes to the right of 136-byte region

The open path has the same loop at :1327 and reports the same way. What is read lands in

nx_tftp_client_error_string, which the application is expected to display or log, so adjacent

packet pool memory ends up in whatever the device does with the error text.

Add (buffer_ptr < packet_ptr -> nx_packet_append_ptr) to the loop condition in all three paths.

Weakness

The product reads data past the end, or before the beginning, of the intended buffer.

Potential Mitigations

• Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
• When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
• Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
• To reduce the likelihood of introducing an out-of-bounds read, ensure that you validate and ensure correct calculations for any length argument, buffer size calculation, or offset. Be especially careful of relying on a sentinel (i.e. special character such as NUL) in untrusted inputs.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/540.html

References

• https://github.com/eclipse-threadx/netxduo/security/advisories/GHSA-wvc9-5m9h-rvxc