Pentesting Tftp

Pentesting TFTP (port 69/UDP)

When to Use

• Default port 69/udp. TFTP is a minimal UDP file-transfer protocol (RFC 1350) with no authentication.
• When nmap -sU/banner shows tftp on 69 (Shodan also labels this port; some scanners mislabel it as bittorrent-tracker).
• Common on large internal networks distributing config files and ROM/firmware images to VoIP phones, routers, switches, and PXE boot infrastructure.

Quick Enumeration

# UDP service detection + path brute force (no directory listing exists)
nmap -n -Pn -sU -p69 -sV --script tftp-enum <IP>

# Manual client probe
tftp <IP>
tftp> get <known_filename> /tmp/out
tftp> put /tmp/test.txt test.txt    # test write access

# Shodan-style discovery marker
#   port:69

Critical: Checks Most Often Missed

• No authentication, ever — any reachable client can attempt read/write. The protocol has no logins.
  • How to CONFIRM: a successful get/put against the server with no credentials.
• No directory listing → must brute-force paths — scanners that don't fuzz miss everything. Use tftp-enum's default-path list and device-specific names.
  • How to CONFIRM: nmap --script tftp-enum <IP> returns found files (it brute-forces common paths).
• Device config / firmware exposure — target known names: running-config, startup-config, <MAC>.cfg, SEP<MAC>.cnf.xml (Cisco VoIP), bootrom.ld, pxelinux.cfg/default, *.bin ROM images. These leak credentials, SNMP strings, and topology.
  • How to CONFIRM: tftp <IP>; get running-config /tmp/rc succeeds and contains secrets.
• Arbitrary write/upload — writable TFTP roots allow overwriting configs/firmware or staging payloads for PXE/device boot.
  • How to CONFIRM: tftp> put payload.bin succeeds, then re-get to verify it landed.

Workflow

Step 1: Enumerate (service + default paths)

nmap -n -Pn -sU -p69 -sV --script tftp-enum <IP>
# Augment with a custom filename list (device-specific names)
nmap -sU -p69 --script tftp-enum --script-args tftp-enum.filelist=tftplist.txt <IP>

Step 2: Access (read/write — no auth step)

# Read a known/guessed file
tftp <IP>
tftp> mode octet            # binary mode for ROM/firmware images
tftp> get running-config /tmp/running-config
tftp> get SEP001122334455.cnf.xml /tmp/phone.xml

# Test write access
tftp> put /tmp/test.txt test.txt

Step 3: Exploit / Extract (download configs, upload payloads)

# Metasploit transfer utility (download or upload)
msfconsole -q -x 'use auxiliary/admin/tftp/tftp_transfer_util; set RHOSTS <IP>; set RPORT 69; set FILENAME running-config; set ACTION Download; run; exit'

# Python (tftpy) for scripted download/upload
python3 - <<'PY'
import tftpy
c = tftpy.TftpClient("<IP>", 69)
c.download("running-config", "/tmp/running-config", timeout=5)
c.upload("payload.bin", "/local/path/payload.bin", timeout=5)
PY

Step 4: Post-access / pivot

• Parse downloaded configs for cleartext/Type-7 passwords, SNMP community strings, and management IPs; reuse on SSH/Telnet/SNMP.
• For PXE environments, inspect pxelinux.cfg/default and boot images for credentials or to assess boot-tampering risk.
• If write is allowed, document the ability to overwrite device firmware/config (high impact) rather than modifying production devices.

Key Concepts

Tools & Systems

Common Scenarios

Scenario 1: Cisco VoIP config disclosure

nmap --script tftp-enum and guessing SEP<MAC>.cnf.xml retrieves a phone config containing the provisioning server and credentials, reused to access the call manager.

Scenario 2: Router running-config leak

tftp <IP>; get running-config downloads a device config with Type-7 passwords and SNMP community strings, decoded and reused against the device's SSH/SNMP interfaces.

Scenario 3: Writable TFTP root

tftp> put payload.bin succeeds, demonstrating that an attacker could overwrite firmware/config images served to provisioned devices — flagged as high impact.

Output Format

## TFTP Finding

**Service**: TFTP
**Port**: 69/udp
**Severity**: High
**Finding**: Unauthenticated read (and write) access exposing device configuration
**Evidence**:
  - nmap tftp-enum found "running-config", "startup-config"
  - tftp get running-config -> contained enable secret + SNMP community "private"
  - tftp put test.txt succeeded (writable root)
**Impact**: Unauthenticated attackers can read device credentials/topology and overwrite served configs/firmware.
**Recommendation**:
  1. Restrict TFTP to provisioning VLANs with ACLs; block UDP/69 from untrusted networks.
  2. Make the TFTP root read-only and serve only non-sensitive files.
  3. Use secure provisioning (HTTPS/SCP) and encrypt/rotate any credentials exposed in configs.