CVE-2026-1977: mcp-vegalite-server RCE Vulnerability

CVE-2026-1977 Overview

A code injection vulnerability has been identified in isaacwasserman mcp-vegalite-server up to commit 16aefed598b8cd897b78e99b907f6e2984572c61. The vulnerability affects the eval function within the visualize_data component, where improper handling of the vegalite_specification argument allows attackers to inject and execute arbitrary code. This flaw can be exploited remotely over the network, posing a significant risk to systems utilizing this visualization server.

Critical Impact

Remote attackers can exploit the code injection vulnerability to execute arbitrary code on affected systems by manipulating the vegalite_specification parameter, potentially leading to full system compromise.

Affected Products

• isaacwasserman mcp-vegalite-server up to commit 16aefed598b8cd897b78e99b907f6e2984572c61

Discovery Timeline

• February 6, 2026 - CVE-2026-1977 published to NVD
• February 6, 2026 - Last updated in NVD database

Technical Details for CVE-2026-1977

Vulnerability Analysis

This vulnerability falls under CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component), commonly known as Injection. The flaw exists in the visualize_data component where user-controlled input passed through the vegalite_specification argument is processed by an eval function without proper sanitization or validation.

The use of eval to process user-supplied data is inherently dangerous, as it allows the interpretation and execution of arbitrary code within the application's runtime context. When attackers craft malicious input disguised as legitimate Vega-Lite specifications, the application executes the injected code with the same privileges as the server process.

The exploit has been publicly disclosed, increasing the urgency for organizations to assess their exposure. The project maintainers were notified through an issue report but have not yet responded.

Root Cause

The root cause of this vulnerability stems from the unsafe use of the eval function to process the vegalite_specification argument in the visualize_data component. The application fails to properly validate, sanitize, or constrain the input before passing it to the evaluation function, creating a direct path for code injection attacks. This represents a fundamental secure coding violation where untrusted input is treated as executable code.

Attack Vector

The vulnerability can be exploited remotely over the network. An attacker with low-level privileges can submit a specially crafted vegalite_specification payload to the visualize_data endpoint. The malicious specification, instead of containing legitimate Vega-Lite visualization parameters, includes injected code that gets executed when the eval function processes the input.

The attack requires no user interaction and can be performed from any network location that can reach the vulnerable server. For technical details on the exploitation mechanism, refer to the GitHub Issue Discussion and the VulDB entry.

Detection Methods for CVE-2026-1977

Indicators of Compromise

• Unusual or malformed requests to the visualize_data endpoint containing code syntax instead of standard Vega-Lite JSON specifications
• Unexpected process spawning or network connections originating from the mcp-vegalite-server process
• Log entries showing attempts to inject shell commands, JavaScript code, or system calls within specification parameters
• Anomalous server behavior such as elevated CPU usage or unauthorized file system access following visualization requests

Detection Strategies

• Implement web application firewall (WAF) rules to detect and block requests containing code injection patterns in the vegalite_specification parameter
• Deploy application-level logging to capture all incoming requests to the visualize_data component for forensic analysis
• Use runtime application self-protection (RASP) solutions to monitor and block eval function calls with suspicious input patterns
• Configure intrusion detection systems (IDS) to alert on network traffic containing potential code injection payloads targeting this endpoint

Monitoring Recommendations

• Enable verbose logging for the mcp-vegalite-server application to capture detailed request information
• Monitor server process behavior for unexpected child processes, file operations, or network connections
• Implement alerting for failed or malformed visualization requests that may indicate reconnaissance or exploitation attempts
• Review access logs periodically for patterns consistent with automated scanning or injection testing

How to Mitigate CVE-2026-1977

Immediate Actions Required

• Assess exposure by identifying all deployments of mcp-vegalite-server in your environment
• Restrict network access to the affected service using firewall rules or network segmentation to limit exposure to trusted sources only
• Implement input validation at the network perimeter using a WAF to filter malicious specification payloads
• Consider temporarily disabling the visualize_data functionality if it is not business-critical until a patch is available

Patch Information

As of the last update, the mcp-vegalite-server project uses a rolling release model and no official patch has been released. The maintainers were notified of the vulnerability through a GitHub issue but have not yet responded. Organizations should monitor the project repository for updates and apply patches as soon as they become available.

Workarounds

• Deploy a reverse proxy with strict input validation to sanitize all requests before they reach the vulnerable component
• Implement application-level sandboxing to limit the potential impact of successful code execution
• Replace the use of eval with safer JSON parsing methods if modifying the source code is feasible in your environment
• Isolate the mcp-vegalite-server in a containerized or virtualized environment with minimal privileges and restricted network access

# Example: Restrict access to mcp-vegalite-server using iptables
# Allow only trusted IP ranges to access the service
iptables -A INPUT -p tcp --dport 3000 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 3000 -j DROP