Cisco IOS / IOS XE / IOS XR / PIX IKEv1 Information Disclosure Vulnerability (CVE-2016-6415, BENIGNCERTAIN)
Executive & SecOps Summary
SECOPS ASSESSMENTCisco IOS 12.2 through 12.4 and 15.0 through 15.6, IOS XE through 3.18S, IOS XR 4.3.x and 5.0.x through 5.2.x, and PIX before 7.0
Unauthenticated remote attackers can retrieve sensitive information from device memory (including private keys and configuration data) by sending crafted IKEv1 negotiation requests
Upgrade affected device firmware to the latest patched releases, or restrict access to UDP ports 500 and 4500 using infrastructure ACLs to trusted peers only
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Administrators must upgrade to a fixed Cisco IOS/IOS XE/IOS XR software release. Verify your current version and perform the upgrade via TFTP/FTP as shown below:
# Check current software version and boot image
show version | include Software
show boot
# Example: Copying a secure patched image from a TFTP server
copy tftp: flash:
# Address or name of remote host? 10.1.1.50
# Source filename? c3900e-universalk9-mz.SPA.156-3.M10.bin
# Destination filename [c3900e-universalk9-mz.SPA.156-3.M10.bin]?
configure terminal
no boot system
boot system flash c3900e-universalk9-mz.SPA.156-3.M10.bin
end
write memory
reload2. Temporary Workaround & Hardening Configuration
If immediate patching is not feasible, implement Infrastructure Access Control Lists (iACLs) to restrict IKEv1 traffic (UDP ports 500 and 4500) only to authorized VPN peers.
# Define ACL to permit only trusted peer (e.g., 203.0.113.50) and deny all other IKE traffic
configure terminal
ip access-list extended SECURE-IKE-ACL
permit udp host 203.0.113.50 any eq non500-isakmp
permit udp host 203.0.113.50 any eq isakmp
deny udp any any eq non500-isakmp
deny udp any any eq isakmp
permit ip any any
exit
# Apply the ACL to the external interface
interface GigabitEthernet0/0
ip access-group SECURE-IKE-ACL in
end
write memory3. Log Audit & IoC Verification Commands
Verify if IKEv1/ISAKMP is active on the device and inspect system logs for potential exploitation attempts or unexpected crashes.
# Check active ISAKMP (IKEv1) security associations
show crypto isakmp sa
show crypto ipsec sa
# Search system logs for unusual IKE negotiations or process crashes
show logging | include ISAKMP|IKE|HEARTBEAT|CrashStop 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 (CVE-2016-6415), widely known as 'BENIGNCERTAIN', is a critical information disclosure vulnerability in the Internet Key Exchange Version 1 (IKEv1) packet processing engine of Cisco IOS, IOS XE, IOS XR, and PIX software. The root cause lies in insufficient input validation and missing boundary checks when handling Security Association (SA) negotiation requests. When a malformed IKEv1 request is received, the system fails to validate the requested payload length, leading to an out-of-bounds read condition.
2. Exploitation Mechanics & Attack Scenario
An attacker exploits this vulnerability by sending a specially crafted IKEv1 SA negotiation packet to an affected device listening on UDP port 500 (ISAKMP) or UDP port 4500 (IPsec NAT-T). The malicious packet contains anomalous parameters or length fields. Because the IKEv1 daemon does not properly bound-check the buffer, it responds by copying adjacent memory segments into the response payload. This allows an unauthenticated remote attacker to dump chunks of volatile memory (RAM), which may contain highly sensitive data such as IPsec pre-shared keys (PSKs), RSA private keys, configuration files, and active session credentials.
3. Infrastructure & Business Impact
As a vulnerability listed in the CISA KEV catalog with an EPSS score exceeding 0.87, this flaw represents an active and severe threat. If an attacker successfully extracts cryptographic keys or configuration details, they can decrypt VPN traffic, perform Man-in-the-Middle (MitM) attacks, or gain unauthorized administrative access to the internal network. This compromises the entire confidentiality and integrity of the enterprise network infrastructure, potentially leading to lateral movement and catastrophic data breaches.
Official Vendor Advisories & References
The server IKEv1 implementation in Cisco IOS 12.2 through 12.4 and 15.0 through 15.6, IOS XE through 3.18S, IOS XR 4.3.x and 5.0.x through 5.2.x, and PIX before 7.0 allows remote attackers to obtain sensitive information from device memory via a Security Association (SA) negotiation request, aka Bug IDs CSCvb29204 and CSCvb36055 or BENIGNCERTAIN.
Frequently Asked SecOps Questions (CVE-2016-6415)
FAQQ1. How critical is CVE-2016-6415 and is it actively exploited in the wild?
CVE-2016-6415 is rated CVSS 7.5 (HIGH) with a 30-day EPSS exploitation probability of 87.7%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2016-6415?
Primary impacted vendors include cisco across ios, ios_xe, ios_xr, pix_firewall_software. Scope summary: Cisco IOS 12.2 through 12.4 and 15.0 through 15.6, IOS XE through 3.18S, IOS XR 4.3.x and 5.0.x through 5.2.x, and PIX before 7.0 with IKEv1 enabled
Q3. What temporary mitigations or workarounds exist for CVE-2016-6415 before patching?
[Mitigation] Upgrade affected device firmware to the latest patched releases, or restrict access to UDP ports 500 and 4500 using infrastructure ACLs to trusted peers only Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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