CVE-2023-39276: SonicWall SonicOS Buffer Overflow Flaw

CVE-2023-39276 Overview

CVE-2023-39276 is a post-authentication stack-based buffer overflow vulnerability discovered in SonicWall SonicOS. The vulnerability exists in the getBookmarkList.json URL endpoint and can be exploited by an authenticated attacker to cause a denial of service condition, resulting in a firewall crash. This vulnerability affects a wide range of SonicWall firewall products across multiple hardware series including NSA, NSSP, NSv, TZ, SM, and SOHO product lines.

Critical Impact

Authenticated attackers can crash SonicWall firewalls by exploiting a stack-based buffer overflow in the bookmark management endpoint, potentially causing network outages and security gaps.

Affected Products

• SonicWall SonicOS (multiple versions across hardware platforms)
• SonicWall NSA Series (NSA2700, NSA3700, NSA4700, NSA5700, NSA6700, NSA_2600, NSA_2650, NSA_3600, NSA_3650, NSA_4600, NSA_4650, NSA_5600, NSA_5650, NSA_6600, NSA_6650)
• SonicWall NSSP Series (NSSP10700, NSSP11700, NSSP13700, NSSP15700)
• SonicWall NSv Series (NSv10, NSv25, NSv50, NSv100, NSv200, NSv270, NSv300, NSv400, NSv470, NSv800, NSv870, NSv1600)
• SonicWall TZ Series (TZ270, TZ270W, TZ370, TZ370W, TZ470, TZ470W, TZ570, TZ570P, TZ570W, TZ670, TZ_300, TZ_300P, TZ_300W, TZ_350, TZ_400, TZ_400W, TZ_500, TZ_500W, TZ_600, TZ_600P)
• SonicWall SM Series (SM_9200, SM_9250, SM_9400, SM_9450, SM_9600, SM_9650)
• SonicWall SOHO Series (SOHO_250, SOHO_250W, SOHOW)

Discovery Timeline

• October 17, 2023 - CVE-2023-39276 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2023-39276

Vulnerability Analysis

This vulnerability is a post-authentication stack-based buffer overflow (CWE-121, CWE-787) that occurs when processing requests to the getBookmarkList.json endpoint in SonicOS. The flaw allows an authenticated attacker with network access to send specially crafted requests that overflow a stack buffer, corrupting memory and causing the firewall to crash.

The attack requires valid authentication credentials, meaning an attacker must first gain access to a legitimate user account on the SonicWall device. Once authenticated, the attacker can trigger the buffer overflow by sending malformed data to the vulnerable endpoint, leading to memory corruption on the stack and subsequent device failure.

Root Cause

The root cause of CVE-2023-39276 is improper input validation and insufficient bounds checking in the getBookmarkList.json endpoint handler. When processing bookmark list requests, the application fails to properly validate the size of input data before copying it to a fixed-size stack buffer. This allows an attacker to supply input that exceeds the allocated buffer space, overwriting adjacent memory on the stack.

The vulnerability is classified under CWE-121 (Stack-based Buffer Overflow) and CWE-787 (Out-of-bounds Write), indicating that the application writes data beyond the boundaries of its allocated stack memory, corrupting the stack frame and causing a denial of service condition.

Attack Vector

The attack vector for this vulnerability involves sending a crafted HTTP request to the /api/sonicos/getBookmarkList.json endpoint on a SonicWall firewall's management interface. The attacker must first authenticate to the device using valid credentials. Once authenticated, the attacker submits a request containing oversized or malformed data that triggers the stack buffer overflow.

When the vulnerable function processes this malicious input without proper bounds checking, the stack is corrupted, leading to an unhandled exception that causes the firewall to crash. In enterprise environments, this can result in network connectivity loss, security policy enforcement gaps, and potential cascading failures in dependent systems.

Detection Methods for CVE-2023-39276

Indicators of Compromise

• Unexpected firewall reboots or crashes shortly after authenticated API requests
• Log entries showing errors or exceptions related to the getBookmarkList.json endpoint
• Anomalous access patterns to the SonicOS management interface from unusual source addresses
• Multiple sequential requests to bookmark-related API endpoints from a single authenticated session

Detection Strategies

• Monitor SonicWall system logs for crash events and unexpected restarts that correlate with management interface activity
• Implement network traffic analysis to detect unusually large or malformed requests to the /api/sonicos/getBookmarkList.json endpoint
• Deploy intrusion detection signatures targeting stack overflow patterns in HTTP POST data to SonicOS management interfaces
• Configure alerting for repeated authentication followed by immediate firewall unavailability

Monitoring Recommendations

• Enable detailed logging on SonicWall management interfaces and forward logs to a SIEM for correlation analysis
• Implement baseline monitoring for firewall uptime and availability to quickly detect exploitation attempts
• Monitor authenticated session activity for anomalous patterns such as rapid API requests to bookmark endpoints
• Establish alerts for management interface access from non-standard administrative IP addresses

How to Mitigate CVE-2023-39276

Immediate Actions Required

• Apply the latest SonicOS firmware update from SonicWall that addresses this vulnerability
• Restrict management interface access to trusted administrative networks using firewall rules or VPN-only access
• Review and audit all user accounts with management interface access, removing unnecessary privileges
• Enable multi-factor authentication for all administrative accounts to reduce risk of credential compromise

Patch Information

SonicWall has released security patches addressing this vulnerability. Administrators should review the SonicWall Vulnerability Advisory SNWLID-2023-0012 for specific firmware versions that contain the fix. Organizations should download and apply the appropriate updated firmware for their specific hardware model through the SonicWall support portal.

Workarounds

• Limit management interface exposure by binding it only to internal management VLANs or out-of-band management networks
• Implement network-level access controls to restrict which IP addresses can reach the SonicOS management interface
• Configure firewall rules to block external access to API endpoints including getBookmarkList.json until patching is complete
• Monitor administrative sessions closely and implement session timeout policies to reduce the window of opportunity for exploitation

# Example: Restrict SonicOS management access to specific admin networks
# Configure access rules in SonicOS management interface:
# 1. Navigate to Network > Interfaces > Edit Management Interface
# 2. Set allowed management IP ranges to trusted admin subnets only
# 3. Disable HTTP/HTTPS management on WAN interfaces
# 4. Enable management access only via internal interfaces or VPN