Cisco IOS and IOS-XE SNMP Buffer Overflow Remote Code Execution Vulnerability (CVE-2017-6742) Security Advisory
Executive & SecOps Summary
SECOPS ASSESSMENTCisco IOS and IOS-XE devices with active SNMP services and exposed valid credentials (community strings or SNMPv3 users)
An authenticated remote attacker can send crafted SNMP packets to trigger a buffer overflow, causing a system reload (DoS) or executing arbitrary code with full administrative privileges
Apply official Cisco software updates, restrict SNMP access using strict Access Control Lists (ACLs), or disable SNMP services if not required
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Upgrading to a non-vulnerable Cisco IOS/IOS-XE release is the recommended permanent fix.
# Example: Downloading and configuring a secure IOS image via TFTP
copy tftp: flash:
Address or name of remote host? 192.168.1.100
Source filename? c3900e-universalk9-mz.SPA.157-3.M9.bin
Destination filename [c3900e-universalk9-mz.SPA.157-3.M9.bin]?
configure terminal
no boot system
boot system flash c3900e-universalk9-mz.SPA.157-3.M9.bin
end
write memory
reload2. Temporary Workaround & Hardening Configuration
If immediate patching is not feasible, disable SNMP or restrict access to authorized management hosts only.
configure terminal
# Option A: Completely disable SNMP services
no snmp-server
# Option B: Restrict SNMP access using an Access Control List (ACL)
ip access-list standard SNMP_ALLOW_ONLY
permit 10.10.100.50
deny any log
exit
snmp-server community SECURE_COMMUNITY_STRING RO SNMP_ALLOW_ONLY
end
write memory3. Log Audit & IoC Verification Commands
Verify the SNMP configuration status and inspect system logs for unexpected reloads or unauthorized SNMP access attempts.
# Check active SNMP configurations and community strings
show running-config | include snmp-server
# Inspect reload history and SNMP-related system logs
show version | include returned to ROM
show logging | include %SYS-5-RELOAD|%SNMPStop 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 exists in the SNMP packet processing engine of Cisco IOS and IOS-XE software. It is classified as a buffer overflow vulnerability (CWE-119) resulting from inadequate bounds checking when copying SNMP packet data into internal memory buffers. The flaw affects all versions of SNMP (v1, v2c, and v3).
2. Exploitation Mechanics & Attack Scenario
To exploit this vulnerability, an attacker must possess valid SNMP credentials. For SNMPv1 and SNMPv2c, the attacker needs to know the read-only (RO) community string; for SNMPv3, valid user credentials are required. The attacker then transmits crafted SNMP packets directly to the UDP port 161 of the target device. Upon processing, the malformed packet triggers a buffer overflow, allowing the attacker to overwrite memory structures to hijack execution flow or crash the system.
3. Infrastructure & Business Impact
As a CISA Known Exploited Vulnerabilities (KEV) catalog entry, this vulnerability has been actively exploited in the wild. Successful exploitation allows complete compromise of critical routing and switching infrastructure, enabling attackers to intercept network traffic, perform Man-in-the-Middle (MitM) attacks, or pivot deeper into the enterprise network.
Official Vendor Advisories & References
A vulnerability in the SNMP implementation of could allow an authenticated, remote attacker to cause a reload of the affected system or to remotely execute code. An attacker could exploit this vulnerability by sending a crafted SNMP packet to the affected device. The vulnerability is due to a buffer overflow in the affected code area. The vulnerability affects all versions of SNMP (versions 1, 2c, and 3). The attacker must know the SNMP read only community string (SNMP version 2c or earlier) or the user credentials (SNMPv3). An exploit could allow the attacker to execute arbitrary code and obtain full control of the system or to cause a reload of the affected system. Only traffic directed to the affected system can be used to exploit this vulnerability.
Frequently Asked SecOps Questions (CVE-2017-6742)
FAQQ1. How critical is CVE-2017-6742 and is it actively exploited in the wild?
CVE-2017-6742 is rated CVSS 8.8 (HIGH) with a 30-day EPSS exploitation probability of 21.3%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2017-6742?
Primary impacted vendors include cisco across ios, ios-xe. Scope summary: All Cisco IOS and IOS-XE software versions with SNMP enabled (affecting SNMPv1, v2c, and v3)
Q3. What temporary mitigations or workarounds exist for CVE-2017-6742 before patching?
[Mitigation] Apply official Cisco software updates, restrict SNMP access using strict Access Control Lists (ACLs), or disable SNMP services if not required Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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