CVE-2026-22320: CLI TFTP Command DoS Vulnerability

CVE-2026-22320 Overview

A stack-based buffer overflow vulnerability exists in the CLI's TFTP file-transfer command handling. This flaw allows a low-privileged attacker with Telnet or SSH access to trigger memory corruption by supplying unexpected or oversized filename input. Exploitation results in the corruption of the internal buffer, causing the CLI and web dashboard to become unavailable and leading to a denial of service condition.

Critical Impact

Successful exploitation of this stack-based buffer overflow causes the CLI and web dashboard to become unavailable, resulting in denial of service for device administrators.

Affected Products

• Devices with CLI-based TFTP file transfer functionality
• Systems exposing Telnet/SSH management interfaces
• Network equipment with vulnerable firmware versions

Discovery Timeline

• 2026-03-18 - CVE-2026-22320 published to NVD
• 2026-03-18 - Last updated in NVD database

Technical Details for CVE-2026-22320

Vulnerability Analysis

This vulnerability is classified as CWE-121: Stack-based Buffer Overflow. The flaw resides in the CLI's TFTP file-transfer command handler, which fails to properly validate the length of filename input before copying it to a stack-allocated buffer. When an attacker with low-privileged access (requiring only Telnet or SSH credentials) provides an oversized or malformed filename, the input exceeds the buffer's allocated space, overwriting adjacent memory on the stack.

The vulnerability requires network access and low-privilege authentication, meaning attackers need valid credentials to access the management interface. However, once authenticated, exploitation is straightforward and does not require user interaction.

Root Cause

The root cause is improper bounds checking in the TFTP command processing logic. The CLI component allocates a fixed-size buffer on the stack for storing the filename parameter but does not verify that user-supplied input fits within this allocated space. This classic buffer overflow pattern allows data to overflow into adjacent stack memory, corrupting program state.

Attack Vector

The attack is executed remotely over the network through authenticated Telnet or SSH sessions. An attacker with low-privileged credentials can:

1. Establish a Telnet or SSH connection to the target device
2. Navigate to the TFTP file transfer command interface
3. Submit an oversized or specially crafted filename parameter
4. Trigger the buffer overflow, corrupting stack memory

The overflow causes the CLI process to crash or become unresponsive, which also impacts the web dashboard functionality, resulting in a complete management interface denial of service. For detailed technical information, refer to the CERT-VDE Security Advisory.

Detection Methods for CVE-2026-22320

Indicators of Compromise

• Unexpected CLI service crashes or restarts following TFTP command execution
• Web dashboard becoming unresponsive or unavailable without scheduled maintenance
• Authentication logs showing repeated access followed by service failures
• Core dumps or crash logs indicating stack corruption in TFTP-related processes

Detection Strategies

• Monitor Telnet/SSH session logs for unusually long command inputs or repeated command attempts
• Implement intrusion detection rules to flag abnormally large filename parameters in TFTP commands
• Deploy endpoint detection solutions capable of identifying buffer overflow exploitation patterns
• Enable crash reporting and alerting for CLI service failures

Monitoring Recommendations

• Configure SIEM alerts for correlating management interface logins with subsequent service disruptions
• Establish baseline metrics for CLI service availability and alert on anomalies
• Monitor network traffic for unusual patterns in management protocol sessions
• Review authentication logs regularly for accounts being used to access TFTP functionality

How to Mitigate CVE-2026-22320

Immediate Actions Required

• Restrict Telnet/SSH access to the device from trusted IP addresses only using firewall rules or ACLs
• Disable TFTP functionality if not required for operations
• Review and minimize user accounts with CLI access privileges
• Implement network segmentation to isolate management interfaces from untrusted networks

Patch Information

Consult the CERT-VDE Security Advisory for vendor-specific patch availability and installation guidance. Apply firmware updates as soon as they become available from your device vendor.

Workarounds

• Disable Telnet access and use SSH only with strong authentication mechanisms
• Implement access control lists (ACLs) to limit management interface access to specific administrator workstations
• Deploy a jump server or bastion host for all management access, adding an additional authentication layer
• Consider disabling the TFTP command functionality through CLI configuration if supported

# Example access restriction configuration (syntax varies by vendor)
# Restrict management access to trusted subnet only
access-list management permit 10.0.0.0/24
access-list management deny any

# Apply to management interface
interface mgmt0
  ip access-group management in

# Disable Telnet, use SSH only
line vty 0 15
  transport input ssh
  no transport input telnet