CVE-2020-3297: Cisco SG250X-24 Auth Bypass Vulnerability

CVE-2020-3297 Overview

A vulnerability in session management for the web-based interface of Cisco Small Business Smart and Managed Switches could allow an unauthenticated, remote attacker to defeat authentication protections and gain unauthorized access to the management interface. The attacker could obtain the privileges of the hijacked session account, which could include administrator privileges on the device. This vulnerability is due to the use of weak entropy generation for session identifier values, enabling attackers to brute-force current session identifiers and take over ongoing administrative sessions.

Critical Impact

Unauthenticated remote attackers can bypass authentication and gain full administrative control over affected Cisco switches by exploiting weak session ID entropy, potentially compromising entire network segments.

Affected Products

• Cisco SG250 Series Smart Switches (SG250-08, SG250-10P, SG250-18, SG250-26, SG250-50 and variants)
• Cisco SG350 Series Managed Switches (SG350-10, SG350-28, SG350X, SG350XG and variants)
• Cisco SG550 Series Stackable Managed Switches (SG550X-24, SG550X-48, SX550X and variants)
• Cisco SF250 Series Smart Switches (SF250-24, SF250-48 and variants)
• Cisco SF350 Series Managed Switches (SF350-48, SF350-48P, SF350-48MP and variants)
• Cisco SG200/SF200 Series Smart Switches
• Cisco SG300/SF300 Series Managed Switches
• Cisco SG500/SF500 Series Stackable Managed Switches

Discovery Timeline

• 2020-07-02 - CVE-2020-3297 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-3297

Vulnerability Analysis

This authentication bypass vulnerability (CWE-287) affects the web-based management interface of Cisco Small Business Smart and Managed Switches. The core issue lies in the session management implementation, which relies on a weak entropy source for generating session identifier values. Session identifiers are tokens used to maintain state between HTTP requests and to authenticate users after initial login. When these identifiers are generated using predictable or low-entropy algorithms, they become susceptible to brute-force attacks.

An attacker targeting this vulnerability does not need any prior authentication or credentials. By systematically attempting session identifier values, the attacker can eventually determine a valid session ID belonging to an authenticated user. Once a valid session is identified, the attacker can hijack that session and assume the identity and privileges of the legitimate user—potentially including full administrative access to the switch.

The vulnerability enables complete compromise of affected network infrastructure. Attackers with administrative access can modify switch configurations, create persistent backdoor accounts, intercept network traffic, disable security features, or pivot to other network devices.

Root Cause

The root cause is improper authentication implementation stemming from weak entropy generation in the session identifier creation process. The session management subsystem fails to utilize cryptographically secure random number generation, resulting in predictable session tokens. This cryptographic weakness violates fundamental security principles for session management, where session IDs must be generated with sufficient randomness (typically 128 bits or more of entropy) to prevent brute-force attacks within practical timeframes.

Attack Vector

The attack is network-based and requires no authentication or user interaction. An attacker with network access to the switch's web management interface can remotely exploit this vulnerability. The attack sequence involves:

1. The attacker identifies a target Cisco Small Business switch with the web management interface exposed
2. The attacker initiates a brute-force attack against the session management mechanism, systematically trying session identifier values
3. Due to weak entropy in session ID generation, the attacker can feasibly enumerate valid session IDs within a practical timeframe
4. Upon discovering a valid session identifier belonging to an authenticated administrator, the attacker reuses that session ID in their HTTP requests
5. The attacker gains full administrative access to the switch management interface with all associated privileges

Detection Methods for CVE-2020-3297

Indicators of Compromise

• Unusual or high-volume HTTP/HTTPS requests to the switch management interface from unexpected source IP addresses
• Multiple authentication sessions appearing to originate from different IP addresses with the same session identifier
• Administrative configuration changes occurring outside of normal change windows or from unrecognized sources
• New administrator accounts created without authorization
• Unexpected changes to VLAN configurations, ACLs, or port settings

Detection Strategies

• Monitor web server logs on affected switches for anomalous patterns of HTTP requests, particularly rapid sequential requests that may indicate brute-force attempts
• Implement network-based detection rules to identify high-volume connections to switch management ports (typically TCP/80 or TCP/443)
• Deploy SIEM correlation rules to detect multiple administrative sessions from geographically disparate locations
• Conduct regular audits of switch configurations and administrator account lists to identify unauthorized changes

Monitoring Recommendations

• Enable and centralize logging for all Cisco Small Business switch management interfaces to a secure SIEM or log management platform
• Configure alerts for authentication anomalies, including multiple failed login attempts followed by successful authentication
• Implement network traffic monitoring at management network segments to detect reconnaissance and brute-force activity
• Establish baseline metrics for normal administrative activity to enable anomaly detection

How to Mitigate CVE-2020-3297

Immediate Actions Required

• Apply Cisco's firmware updates immediately to all affected switch models as outlined in the Cisco Security Advisory
• Restrict management interface access to trusted IP addresses using access control lists (ACLs) until patching is complete
• Disable HTTP management access and use HTTPS only; consider disabling web-based management entirely if not required
• Monitor for signs of compromise and review switch configurations for unauthorized changes
• Implement network segmentation to isolate switch management interfaces from general user networks

Patch Information

Cisco has released firmware updates addressing this vulnerability. Administrators should consult the Cisco Security Advisory for CVE-2020-3297 to determine the appropriate fixed firmware version for their specific switch model. The advisory covers the SG200, SG250, SG300, SG350, SG500, SG550, SF200, SF250, SF300, SF350, SF500, SF550, and SX550 series switches with their respective firmware versions.

Workarounds

• Restrict web management interface access to dedicated out-of-band management networks that are not accessible from untrusted network segments
• Implement firewall rules or switch ACLs to allow management access only from specific trusted administrator IP addresses or subnets
• Disable the web-based management interface and use CLI-based management via SSH if web access is not operationally required
• Reduce active session timeout values to minimize the window of opportunity for session hijacking

# Example ACL configuration to restrict management access (Cisco CLI)
# Limit management interface access to trusted management subnet
access-list 10 permit 192.168.100.0 0.0.0.255
access-list 10 deny any log
line vty 0 15
 access-class 10 in