CVE-2025-1691: MongoDB Mongosh XSS Vulnerability

CVE-2025-1691 Overview

The MongoDB Shell (mongosh) is susceptible to a control character injection vulnerability that allows attackers with control of the autocomplete feature to input and execute obfuscated malicious text. This vulnerability requires user interaction where the user must use the 'tab' key to autocomplete text that is a prefix of the attacker's prepared autocompletion payload. The vulnerability is exploitable only when mongosh is connected to a cluster that is partially or fully controlled by an attacker.

Critical Impact
Attackers controlling a MongoDB cluster can leverage the autocomplete feature to inject and execute obfuscated malicious commands when users interact with tab completion, potentially compromising system integrity.

Affected Products

MongoDB Shell (mongosh) versions prior to 2.3.9

Discovery Timeline

2025-02-27 - CVE-2025-1691 published to NVD
2025-09-22 - Last updated in NVD database

Technical Details for CVE-2025-1691

Vulnerability Analysis

This vulnerability falls under CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component), commonly known as an Injection vulnerability. The MongoDB Shell's autocomplete functionality fails to properly sanitize or validate control characters in autocompletion suggestions, allowing malicious content to be injected and executed.

The attack scenario requires a specific setup where the attacker has control over the MongoDB cluster to which the victim connects. By manipulating the autocomplete suggestions returned by the cluster, the attacker can craft payloads containing obfuscated malicious text that becomes active when the user triggers the tab completion feature.

The network-based attack vector combined with the requirement for user interaction (pressing tab to autocomplete) creates a social engineering component to the exploitation. While the vulnerability does not directly impact confidentiality or availability, it poses a significant integrity risk as attackers can execute arbitrary commands within the shell context.

Root Cause

The root cause of this vulnerability lies in insufficient input validation and sanitization of control characters within the mongosh autocomplete feature. The shell fails to properly neutralize special characters in autocompletion suggestions before presenting them to users or executing the completed commands. This allows an attacker who controls the cluster to inject crafted payloads that bypass normal input validation through the trusted autocomplete mechanism.

Attack Vector

The attack requires the following conditions to be met:

The attacker must have partial or full control over a MongoDB cluster
The victim must connect their mongosh client to the attacker-controlled cluster
The victim must type text that serves as a prefix to the attacker's malicious autocompletion
The victim must press 'tab' to trigger the autocomplete feature

When these conditions are met, the attacker's obfuscated malicious text is injected through the autocomplete suggestion and executed when the user accepts the completion. The network-based attack vector allows remote exploitation, though the requirement for user interaction and a controlled cluster environment limits the attack surface.

Detection Methods for CVE-2025-1691

Indicators of Compromise

Unexpected or unusual autocomplete suggestions appearing in mongosh sessions
Presence of non-printable or control characters in command history logs
Suspicious commands executed through mongosh that users don't recall initiating
Network connections from mongosh to unknown or untrusted MongoDB clusters

Detection Strategies

Monitor mongosh command history files for unusual patterns or obfuscated commands
Implement network monitoring to detect connections to unauthorized MongoDB clusters
Review MongoDB server logs for unexpected command executions that may indicate injection attacks
Deploy endpoint detection solutions to monitor shell process behavior for anomalous activity

Monitoring Recommendations

Enable verbose logging for mongosh sessions to capture all command inputs and outputs
Implement allowlisting for approved MongoDB cluster connections to prevent connections to attacker-controlled instances
Configure alerting for unusual command patterns or control character sequences in shell interactions
Regularly audit connection configurations and credentials used by mongosh clients

How to Mitigate CVE-2025-1691

Immediate Actions Required

Upgrade MongoDB Shell (mongosh) to version 2.3.9 or later immediately
Audit all mongosh connections to ensure they point only to trusted, verified MongoDB clusters
Review recent command history for signs of exploitation or suspicious activity
Restrict network access to prevent mongosh from connecting to unauthorized clusters

Patch Information

MongoDB has addressed this vulnerability in mongosh version 2.3.9 and later releases. Users should upgrade to the latest available version to remediate this issue. For detailed patch information and release notes, refer to the MongoDB Issue Tracking advisory.

Workarounds

Avoid connecting mongosh to untrusted or partially trusted MongoDB clusters until patching is complete
Disable or avoid using the tab autocomplete feature when connected to clusters not fully under your organization's control
Implement network segmentation to restrict mongosh client access to only approved MongoDB instances
Use connection strings with explicit server addresses rather than relying on service discovery mechanisms

bash

# Verify mongosh version and upgrade if necessary
mongosh --version
# If version is below 2.3.9, upgrade using your package manager
# For npm installations:
npm update -g mongosh
# For homebrew installations:
brew upgrade mongosh