CVE-2026-27190: Deno Runtime Command Injection RCE Flaw

CVE-2026-27190 Overview

A command injection vulnerability has been identified in Deno's node:child_process implementation. Deno, a modern JavaScript, TypeScript, and WebAssembly runtime designed with security in mind, contains a flaw in how shell arguments are processed when spawning child processes. Prior to version 2.6.8, insufficient escaping of shell arguments allows attackers to inject arbitrary commands through crafted input, potentially leading to unauthorized command execution on the underlying system.

Critical Impact

Attackers can exploit this command injection vulnerability to execute arbitrary system commands, potentially compromising server integrity, stealing sensitive data, or establishing persistent access to affected systems running Deno applications that utilize the node:child_process module.

Affected Products

• Deno versions prior to 2.6.8
• Applications using node:child_process module with shell option enabled
• Node.js compatibility layer implementations in Deno

Discovery Timeline

• February 20, 2026 - CVE-2026-27190 published to NVD
• February 23, 2026 - Last updated in NVD database

Technical Details for CVE-2026-27190

Vulnerability Analysis

This command injection vulnerability (CWE-78) exists in Deno's Node.js compatibility layer, specifically within the node:child_process polyfill implementation. The flaw occurs when the shell option is enabled and arguments are passed to child process spawn functions. The vulnerability allows attackers to break out of the intended command context by injecting shell metacharacters.

The attack requires network access and exploitation complexity is considered high, as specific conditions must be met—namely, the target application must use the affected child_process functions with shell mode enabled and pass user-controllable input as arguments. Successful exploitation can result in complete compromise of confidentiality, integrity, and availability of the affected system.

Root Cause

The root cause lies in the improper handling of shell arguments in the ext/node/polyfills/internal/child_process.ts file. When the shell option is set to true, the original implementation simply joined the file path and arguments with spaces using ArrayPrototypeJoin([file, ...args], " ") without properly escaping shell-special characters. This allowed attackers to inject additional commands or modify the intended command structure through carefully crafted input containing shell metacharacters such as semicolons, pipes, or backticks.

Attack Vector

The attack vector is network-based, targeting Deno applications that expose functionality utilizing child_process methods with shell interpretation enabled. An attacker can supply malicious input containing shell metacharacters that, when concatenated without proper escaping, results in unintended command execution. Common injection patterns include using ; to chain commands, | to pipe output, or $() for command substitution.

   ]);
 
   if (options.shell) {
-    let command = ArrayPrototypeJoin([file, ...args], " ");
+    // When args are provided, escape them to prevent shell injection.
+    // When no args are provided (just a string command), the user intends
+    // for shell interpretation, so don't escape.
+    let command;
+    if (args.length > 0) {
+      const escapedParts = [escapeShellArg(file), ...args.map(escapeShellArg)];
+      command = ArrayPrototypeJoin(escapedParts, " ");
+    } else {
+      command = file;
+    }
     // Transform Node.js flags to Deno equivalents in shell commands that invoke Deno
     command = transformDenoShellCommand(command, options.env);
     // Set the shell, switches, and commands.

Source: GitHub Deno Commit Update

Detection Methods for CVE-2026-27190

Indicators of Compromise

• Unexpected child processes spawned by Deno applications with unusual command-line arguments
• Log entries showing malformed or suspicious command strings containing shell metacharacters (;, |, &, $(), backticks)
• Network traffic patterns indicating command-and-control communication from Deno process contexts
• Unauthorized file system modifications or data exfiltration originating from Deno runtime processes

Detection Strategies

• Implement application-level logging for all child_process invocations, capturing the full command and arguments being executed
• Deploy runtime application self-protection (RASP) solutions to monitor and block suspicious shell command patterns
• Use SentinelOne's Singularity Platform to detect anomalous process spawning behavior and command injection attack patterns
• Monitor for process trees where Deno spawns unexpected shell interpreters (bash, sh, cmd.exe, powershell)

Monitoring Recommendations

• Enable audit logging for all process creation events on systems running Deno applications
• Configure alerts for Deno processes spawning child processes with shell metacharacters in arguments
• Implement network segmentation and monitor egress traffic from application servers running vulnerable Deno versions
• Use SentinelOne's behavioral AI to identify post-exploitation activities following potential command injection attacks

How to Mitigate CVE-2026-27190

Immediate Actions Required

• Upgrade Deno to version 2.6.8 or later immediately on all affected systems
• Audit application code for usage of node:child_process functions with the shell option enabled
• Implement input validation and sanitization for any user-controllable data passed to child process functions
• Consider disabling shell mode (shell: false) where direct execution is sufficient

Patch Information

The vulnerability is fixed in Deno version 2.6.8. The patch implements proper shell argument escaping using a new escapeShellArg() function that sanitizes arguments when the shell option is enabled and arguments are provided. This ensures shell metacharacters are properly escaped, preventing injection attacks while preserving intentional shell interpretation when only a command string is provided without arguments.

For detailed patch information, refer to the GitHub Deno Release v2.6.8 and the GitHub Security Advisory GHSA-hmh4-3xvx-q5hr.

Workarounds

• Avoid using the shell: true option in child_process functions when not strictly necessary
• Implement application-layer input validation to reject inputs containing shell metacharacters before they reach child_process calls
• Use allowlists for permitted commands and arguments rather than blocklists for dangerous characters
• Deploy Web Application Firewalls (WAF) to filter requests containing potential command injection payloads

# Check current Deno version
deno --version

# Upgrade Deno to patched version
deno upgrade --version 2.6.8

# Verify upgrade was successful
deno --version