Cisco IOS and IOS XE SNMP Subsystem Remote Code Execution Vulnerability (CVE-2017-6743)
Executive & SecOps Summary
SECOPS ASSESSMENTCisco IOS and IOS XE Software with SNMP enabled and affected MIBs/OIDs not explicitly excluded
Authenticated remote attackers can execute arbitrary code with full system privileges or trigger a device reload (DoS) via crafted SNMP packets
Apply official Cisco software updates, restrict SNMP access using ACLs, enforce strong community strings/credentials, or disable vulnerable MIB views
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Verify the current software version and upgrade to a fixed release recommended by the Cisco IOS Software Checker.
# Check current IOS version and boot image
show version
show flash:
# Download the fixed image from TFTP and configure boot path
copy tftp: flash:
# (Enter TFTP server IP and the secure target image filename)
configure terminal
no boot system
boot system flash:c3750e-universalk9-mz.152-4.E10.bin
exit
write memory
reload2. Temporary Workaround & Hardening Configuration
If patching is not immediately feasible, restrict SNMP access using Access Control Lists (ACLs) and exclude vulnerable MIBs.
configure terminal
# 1. Define an ACL to restrict SNMP access to trusted hosts only
ip access-list standard SNMP_ALLOW_LIST
permit 192.168.10.50
deny any log
exit
# 2. Remove default community strings and apply ACL to a strong community string
no snmp-server community public RO
snmp-server community Complex_RO_String RO SNMP_ALLOW_LIST
# 3. Exclude vulnerable MIB views (Example)
snmp-server view restrict-view 1.3.6.1.2.1.1 excluded
snmp-server community Complex_RO_String view restrict-view RO SNMP_ALLOW_LIST
end
write memory3. Log Audit & IoC Verification Commands
Inspect system logs and SNMP statistics for signs of exploitation or unexpected reloads.
# Inspect SNMP statistics and error counters
show snmp
# Search system logs for SNMP anomalies or unexpected reloads
show logging | include SNMP|reload|ExceptionStop Exposing VPN Ports to the Internet — Switch to Zero-Trust Access
Eliminate public-facing VPN concentrators and firewall management ports with identity-first Zero-Trust Network Access.
Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability is a buffer overflow (CWE-119) within the Simple Network Management Protocol (SNMP) subsystem of Cisco IOS and IOS XE Software. The root cause is insufficient boundary validation of input data when processing crafted SNMP packets, affecting all versions of SNMP (v1, v2c, and v3).
2. Exploitation Mechanics & Attack Scenario
An attacker exploits this vulnerability by sending a specially crafted SNMP packet via IPv4 or IPv6 directly to the target system. To successfully execute the attack, authentication is required: for SNMP v1/v2c, the attacker must know the read-only community string; for SNMP v3, valid user credentials are required. Upon receiving the malicious OID request, the SNMP subsystem buffer overflows, allowing arbitrary code execution or causing the device to reload.
3. Infrastructure & Business Impact
With a CVSS score of 8.8 (High) and its inclusion in the CISA Known Exploited Vulnerabilities (KEV) catalog, this vulnerability poses a severe threat. Successful exploitation allows complete compromise of the network infrastructure, enabling attackers to intercept traffic, manipulate routing tables, or pivot deeper into the enterprise network.
Official Vendor Advisories & References
The Simple Network Management Protocol (SNMP) subsystem of Cisco IOS and IOS XE Software contains multiple vulnerabilities that could allow an authenticated, remote attacker to remotely execute code on an affected system or cause an affected system to reload. An attacker could exploit these vulnerabilities by sending a crafted SNMP packet to an affected system via IPv4 or IPv6. Only traffic directed to an affected system can be used to exploit these vulnerabilities. The vulnerabilities are due to a buffer overflow condition in the SNMP subsystem of the affected software. The vulnerabilities affect all versions of SNMP - Versions 1, 2c, and 3. To exploit these vulnerabilities via SNMP Version 2c or earlier, the attacker must know the SNMP read-only community string for the affected system. To exploit these vulnerabilities via SNMP Version 3, the attacker must have user credentials for the affected system. A successful exploit could allow the attacker to execute arbitrary code and obtain full control of the affected system or cause the affected system to reload. Customers are advised to apply the workaround as contained in the Workarounds section below. Fixed software information is available via the Cisco IOS Software Checker. All devices that have enabled SNMP and have not explicitly excluded the affected MIBs or OIDs should be considered vulnerable. There are workarounds that address these vulnerabilities.
Frequently Asked SecOps Questions (CVE-2017-6743)
FAQQ1. How critical is CVE-2017-6743 and is it actively exploited in the wild?
CVE-2017-6743 is rated CVSS 8.8 (HIGH) with a 30-day EPSS exploitation probability of 10.8%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2017-6743?
Primary impacted vendors include cisco across ios, ios_xe. Scope summary: All versions of Cisco IOS and IOS XE Software where SNMP is enabled and affected MIBs are not excluded
Q3. What temporary mitigations or workarounds exist for CVE-2017-6743 before patching?
[Mitigation] Apply official Cisco software updates, restrict SNMP access using ACLs, enforce strong community strings/credentials, or disable vulnerable MIB views Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
Generate an Internal Engineering Notice or CISO Report for CVE-2017-6743
Instantly format this advisory into an executive CISO summary or engineering patch ticket.
🔗 Related Advisories in Similar Stack (cisco)
View Category →Cisco Identity Services Engine (ISE) Critical Authentication Bypass Vulnerability (CVE-2026-76460)
[Affected Scope] Cisco Identity Services Engine (ISE) web-based management interface and API endpoints.
Cisco Catalyst SD-WAN Peering Authentication Bypass Vulnerability (CVE-2026-20182)
[Affected Scope] Cisco Catalyst SD-WAN Controller (formerly vSmart), Manager (formerly vManage), and Validator (formerly vBond)
Cisco Secure Firewall Management Center (FMC) Insecure Deserialization Vulnerability (CVE-2026-20131, CVSS 10.0) - Remote Code Execution and Root Privilege Escalation
[Affected Scope] Web-based management interface of Cisco Secure Firewall Management Center (FMC) Software.
Cisco Secure Firewall Management Center (FMC) Authentication Bypass and Root RCE Vulnerability (CVE-2026-20079)
[Affected Scope] Web-based management interface of Cisco Secure Firewall Management Center (FMC) Software
Subscribe to Daily Vulnerability Briefings & KEV Alerts
Concise morning briefings for SecOps, DevSecOps, and SRE teams covering newly exploited CVEs and mitigation priorities.