The TFTP server accepts a DATA datagram of any size.
- Published
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
- Exploitation: none
- Automatable: yes
- Technical impact: partial
Summary
The TFTP server accepts a DATA datagram of any size. The dispatcher rejects datagrams shorter than four bytes (nxd_tftp_server.c:1037) and nothing anywhere checks an upper bound, in particular not against the protocol maximum of 4 + NX_TFTP_FILE_TRANSFER_MAX. Two things follow from that one missing check, both reachable before any authentication because TFTP has none. The handler passes `nx_packet_length - 4` straight to FileX: ```c /* addons/tftp/nxd_tftp_server.c:1863, 1889 */ status = nx_packet_copy(packet_ptr, &temp_ptr, server_ptr -> nx_tftp_server_packet_pool_ptr, NX_WAIT_FOREVER); ... fx_file_write(&(client_request_ptr -> nx_tftp_client_request_file), packet_ptr -> nx_packet_prepend_ptr + 4, packet_ptr -> nx_packet_length - 4); ``` `nx_packet_length` is the length of a chain, not of one contiguous buffer, so FileX copies past the end of the first packet: ``` ERROR: AddressSanitizer: heap-buffer-overflow READ of size 1280 at 0x621000001108 thread T5 #0 __interceptor_memcpy #1 _fx_utility_memory_copy filex/common/src/fx_utility_memory_copy.c:78 0x621000001108 is 0 bytes to the right of 4104-byte region ``` Those bytes are written into the file the attacker is uploading, and a TFTP read request hands them back, so this is a memory disclosure with a convenient retrieval channel. The same datagram also wedges the server. `nx_packet_copy` at :1863 needs ceil(nx_packet_length / pool_payload) packets and asks for them with NX_WAIT_FOREVER, so when the attacker sizes the datagram beyond what the pool holds, the server thread suspends and never returns. A liveness probe after one such datagram times out with the pool at 0 of 12 packets and the server thread suspended, and no later client is served. Reject `nx_packet_length > 4 + NX_TFTP_FILE_TRANSFER_MAX` in the DATA branch before either call, and use a bounded wait rather than NX_WAIT_FOREVER for the copy.
Timeline
- CVE published
- CISA SSVC assessment
Exploitation: none · Automatable: yes · Technical impact: partial
- Record last updated
Affected versions
- NetX Duo
through 6.5.1.202602