diff --git a/packages/core/src/tools/shell.test.ts b/packages/core/src/tools/shell.test.ts
index 9f83b00bb6..dd49a9c800 100644
--- a/packages/core/src/tools/shell.test.ts
+++ b/packages/core/src/tools/shell.test.ts
@@ -210,7 +210,7 @@ describe('ShellTool', () => {
         mockShellOutputCallback = callback;
         const match = cmd.match(/pgrep -g 0 >([^ ]+)/);
         if (match) {
-          extractedTmpFile = match[1].replace(/['"]/g, ''); // remove any quotes if present
+          extractedTmpFile = match[1].replace(/['"]/g, '');
         }
         return {
           pid: 12345,
@@ -994,7 +994,6 @@ EOF`;
       const result = await promise;
       expect(result.llmContent).not.toContain('Process Group PGID:');
     });
-
     it('should have minimal output for successful command', async () => {
       const invocation = shellTool.build({ command: 'echo hello' });
       const promise = invocation.execute({ abortSignal: mockAbortSignal });
@@ -1222,4 +1221,399 @@ EOF`;
       expect(schema.description).toMatchSnapshot();
     });
   });
+
+  describe('command injection detection', () => {
+    it('should block $() command substitution', async () => {
+      const tool = new ShellTool(mockConfig, createMockMessageBus());
+      const invocation = tool.build({ command: 'echo $(whoami)' });
+      const result = await invocation.execute({
+        abortSignal: new AbortController().signal,
+      });
+      expect(result.returnDisplay).toContain('Blocked');
+    });
+
+    it('should block backtick command substitution', async () => {
+      const tool = new ShellTool(mockConfig, createMockMessageBus());
+      const invocation = tool.build({ command: 'echo `whoami`' });
+      const result = await invocation.execute({
+        abortSignal: new AbortController().signal,
+      });
+      expect(result.returnDisplay).toContain('Blocked');
+    });
+
+    it('should allow normal commands without substitution', async () => {
+      mockShellExecutionService.mockImplementation((_cmd, _cwd, _callback) => ({
+        pid: 12345,
+        result: Promise.resolve({
+          output: 'hello',
+          rawOutput: Buffer.from('hello'),
+          exitCode: 0,
+          signal: null,
+          error: null,
+          aborted: false,
+          pid: 12345,
+          executionMethod: 'child_process',
+          backgrounded: false,
+        }),
+      }));
+      const tool = new ShellTool(mockConfig, createMockMessageBus());
+      const invocation = tool.build({ command: 'echo hello' });
+      const result = await invocation.execute({
+        abortSignal: new AbortController().signal,
+      });
+      expect(result.returnDisplay).not.toContain('Blocked');
+    });
+
+    it('should allow single quoted strings with special chars', async () => {
+      mockShellExecutionService.mockImplementation((_cmd, _cwd, _callback) => ({
+        pid: 12345,
+        result: Promise.resolve({
+          output: '$(not substituted)',
+          rawOutput: Buffer.from('$(not substituted)'),
+          exitCode: 0,
+          signal: null,
+          error: null,
+          aborted: false,
+          pid: 12345,
+          executionMethod: 'child_process',
+          backgrounded: false,
+        }),
+      }));
+      const tool = new ShellTool(mockConfig, createMockMessageBus());
+      const invocation = tool.build({
+        command: "echo '$(not substituted)'",
+      });
+      const result = await invocation.execute({
+        abortSignal: new AbortController().signal,
+      });
+      expect(result.returnDisplay).not.toContain('Blocked');
+    });
+
+    it('should allow escaped backtick outside double quotes', async () => {
+      mockShellExecutionService.mockImplementation((_cmd, _cwd, _callback) => ({
+        pid: 12345,
+        result: Promise.resolve({
+          output: 'hello',
+          rawOutput: Buffer.from('hello'),
+          exitCode: 0,
+          signal: null,
+          error: null,
+          aborted: false,
+          pid: 12345,
+          executionMethod: 'child_process',
+          backgrounded: false,
+        }),
+      }));
+      const tool = new ShellTool(mockConfig, createMockMessageBus());
+      const invocation = tool.build({ command: 'echo \\`hello\\`' });
+      const result = await invocation.execute({
+        abortSignal: new AbortController().signal,
+      });
+      expect(result.returnDisplay).not.toContain('Blocked');
+    });
+
+    it('should block $() inside double quotes', async () => {
+      const tool = new ShellTool(mockConfig, createMockMessageBus());
+      const invocation = tool.build({ command: 'echo "$(whoami)"' });
+      const result = await invocation.execute({
+        abortSignal: new AbortController().signal,
+      });
+      expect(result.returnDisplay).toContain('Blocked');
+    });
+
+    it('should block >() process substitution', async () => {
+      const tool = new ShellTool(mockConfig, createMockMessageBus());
+      const invocation = tool.build({ command: 'echo >(whoami)' });
+      const result = await invocation.execute({
+        abortSignal: new AbortController().signal,
+      });
+      expect(result.returnDisplay).toContain('Blocked');
+    });
+
+    it('should allow $() inside single quotes', async () => {
+      mockShellExecutionService.mockImplementation((_cmd, _cwd, _callback) => ({
+        pid: 12345,
+        result: Promise.resolve({
+          output: '$(whoami)',
+          rawOutput: Buffer.from('$(whoami)'),
+          exitCode: 0,
+          signal: null,
+          error: null,
+          aborted: false,
+          pid: 12345,
+          executionMethod: 'child_process',
+          backgrounded: false,
+        }),
+      }));
+      const tool = new ShellTool(mockConfig, createMockMessageBus());
+      const invocation = tool.build({
+        command: "echo '$(whoami)'",
+      });
+      const result = await invocation.execute({
+        abortSignal: new AbortController().signal,
+      });
+      expect(result.returnDisplay).not.toContain('Blocked');
+    });
+    it('should block PowerShell @() array subexpression', async () => {
+      mockPlatform.mockReturnValue('win32');
+      const tool = new ShellTool(mockConfig, createMockMessageBus());
+      const invocation = tool.build({ command: 'echo @(whoami)' });
+      const result = await invocation.execute({
+        abortSignal: new AbortController().signal,
+      });
+      expect(result.returnDisplay).toContain('Blocked');
+    });
+
+    it('should block PowerShell $() subexpression', async () => {
+      mockPlatform.mockReturnValue('win32');
+      const tool = new ShellTool(mockConfig, createMockMessageBus());
+      const invocation = tool.build({ command: 'echo $(whoami)' });
+      const result = await invocation.execute({
+        abortSignal: new AbortController().signal,
+      });
+      expect(result.returnDisplay).toContain('Blocked');
+    });
+
+    it('should allow PowerShell single quoted strings', async () => {
+      mockPlatform.mockReturnValue('win32');
+      mockShellExecutionService.mockImplementation((_cmd, _cwd, _callback) => ({
+        pid: 12345,
+        result: Promise.resolve({
+          output: '$(whoami)',
+          rawOutput: Buffer.from('$(whoami)'),
+          exitCode: 0,
+          signal: null,
+          error: null,
+          aborted: false,
+          pid: 12345,
+          executionMethod: 'child_process',
+          backgrounded: false,
+        }),
+      }));
+      const tool = new ShellTool(mockConfig, createMockMessageBus());
+      const invocation = tool.build({
+        command: "echo '$(whoami)'",
+      });
+      const result = await invocation.execute({
+        abortSignal: new AbortController().signal,
+      });
+      expect(result.returnDisplay).not.toContain('Blocked');
+    });
+    it('should allow escaped substitution outside quotes', async () => {
+      mockShellExecutionService.mockImplementation((_cmd, _cwd, _callback) => ({
+        pid: 12345,
+        result: Promise.resolve({
+          output: '$(whoami)',
+          rawOutput: Buffer.from('$(whoami)'),
+          exitCode: 0,
+          signal: null,
+          error: null,
+          aborted: false,
+          pid: 12345,
+          executionMethod: 'child_process',
+          backgrounded: false,
+        }),
+      }));
+      const tool = new ShellTool(mockConfig, createMockMessageBus());
+      const invocation = tool.build({ command: 'echo \\$(whoami)' });
+      const result = await invocation.execute({
+        abortSignal: new AbortController().signal,
+      });
+      expect(result.returnDisplay).not.toContain('Blocked');
+    });
+
+    it('should allow process substitution inside double quotes', async () => {
+      mockShellExecutionService.mockImplementation((_cmd, _cwd, _callback) => ({
+        pid: 12345,
+        result: Promise.resolve({
+          output: '<(whoami)',
+          rawOutput: Buffer.from('<(whoami)'),
+          exitCode: 0,
+          signal: null,
+          error: null,
+          aborted: false,
+          pid: 12345,
+          executionMethod: 'child_process',
+          backgrounded: false,
+        }),
+      }));
+      const tool = new ShellTool(mockConfig, createMockMessageBus());
+      const invocation = tool.build({ command: 'echo "<(whoami)"' });
+      const result = await invocation.execute({
+        abortSignal: new AbortController().signal,
+      });
+      expect(result.returnDisplay).not.toContain('Blocked');
+    });
+
+    it('should block process substitution without quotes', async () => {
+      const tool = new ShellTool(mockConfig, createMockMessageBus());
+      const invocation = tool.build({ command: 'echo <(whoami)' });
+      const result = await invocation.execute({
+        abortSignal: new AbortController().signal,
+      });
+      expect(result.returnDisplay).toContain('Blocked');
+    });
+
+    it('should allow escaped $() outside double quotes', async () => {
+      mockShellExecutionService.mockImplementation((_cmd, _cwd, _callback) => ({
+        pid: 12345,
+        result: Promise.resolve({
+          output: '$(whoami)',
+          rawOutput: Buffer.from('$(whoami)'),
+          exitCode: 0,
+          signal: null,
+          error: null,
+          aborted: false,
+          pid: 12345,
+          executionMethod: 'child_process',
+          backgrounded: false,
+        }),
+      }));
+      const tool = new ShellTool(mockConfig, createMockMessageBus());
+      const invocation = tool.build({ command: 'echo \\$(whoami)' });
+      const result = await invocation.execute({
+        abortSignal: new AbortController().signal,
+      });
+      expect(result.returnDisplay).not.toContain('Blocked');
+    });
+
+    it('should allow output process substitution inside double quotes', async () => {
+      mockShellExecutionService.mockImplementation((_cmd, _cwd, _callback) => ({
+        pid: 12345,
+        result: Promise.resolve({
+          output: '<(whoami)',
+          rawOutput: Buffer.from('<(whoami)'),
+          exitCode: 0,
+          signal: null,
+          error: null,
+          aborted: false,
+          pid: 12345,
+          executionMethod: 'child_process',
+          backgrounded: false,
+        }),
+      }));
+      const tool = new ShellTool(mockConfig, createMockMessageBus());
+      const invocation = tool.build({ command: 'echo "<(whoami)"' });
+      const result = await invocation.execute({
+        abortSignal: new AbortController().signal,
+      });
+      expect(result.returnDisplay).not.toContain('Blocked');
+    });
+
+    it('should block <() process substitution without quotes', async () => {
+      const tool = new ShellTool(mockConfig, createMockMessageBus());
+      const invocation = tool.build({ command: 'echo <(whoami)' });
+      const result = await invocation.execute({
+        abortSignal: new AbortController().signal,
+      });
+      expect(result.returnDisplay).toContain('Blocked');
+    });
+    it('should block PowerShell bare () grouping operator', async () => {
+      mockPlatform.mockReturnValue('win32');
+      const tool = new ShellTool(mockConfig, createMockMessageBus());
+      const invocation = tool.build({ command: 'echo (whoami)' });
+      const result = await invocation.execute({
+        abortSignal: new AbortController().signal,
+      });
+      expect(result.returnDisplay).toContain('Blocked');
+    });
+
+    it('should allow escaped $() inside double quotes', async () => {
+      mockShellExecutionService.mockImplementation((_cmd, _cwd, _callback) => ({
+        pid: 12345,
+        result: Promise.resolve({
+          output: '$(whoami)',
+          rawOutput: Buffer.from('$(whoami)'),
+          exitCode: 0,
+          signal: null,
+          error: null,
+          aborted: false,
+          pid: 12345,
+          executionMethod: 'child_process',
+          backgrounded: false,
+        }),
+      }));
+      const tool = new ShellTool(mockConfig, createMockMessageBus());
+      const invocation = tool.build({ command: 'echo "\\$(whoami)"' });
+      const result = await invocation.execute({
+        abortSignal: new AbortController().signal,
+      });
+      expect(result.returnDisplay).not.toContain('Blocked');
+    });
+
+    it('should allow escaped substitution inside double quotes', async () => {
+      mockShellExecutionService.mockImplementation((_cmd, _cwd, _callback) => ({
+        pid: 12345,
+        result: Promise.resolve({
+          output: '$(whoami)',
+          rawOutput: Buffer.from('$(whoami)'),
+          exitCode: 0,
+          signal: null,
+          error: null,
+          aborted: false,
+          pid: 12345,
+          executionMethod: 'child_process',
+          backgrounded: false,
+        }),
+      }));
+      const tool = new ShellTool(mockConfig, createMockMessageBus());
+      const invocation = tool.build({ command: 'echo "\\$(whoami)"' });
+      const result = await invocation.execute({
+        abortSignal: new AbortController().signal,
+      });
+      expect(result.returnDisplay).not.toContain('Blocked');
+    });
+
+    it('should allow PowerShell keyword with flag e.g. switch -regex ($x)', async () => {
+      mockPlatform.mockReturnValue('win32');
+      mockShellExecutionService.mockImplementation((_cmd, _cwd, _callback) => ({
+        pid: 12345,
+        result: Promise.resolve({
+          output: 'result',
+          rawOutput: Buffer.from('result'),
+          exitCode: 0,
+          signal: null,
+          error: null,
+          aborted: false,
+          pid: 12345,
+          executionMethod: 'child_process',
+          backgrounded: false,
+        }),
+      }));
+      const tool = new ShellTool(mockConfig, createMockMessageBus());
+      const invocation = tool.build({
+        command: 'switch -regex ($x) { "a" { 1 } }',
+      });
+      const result = await invocation.execute({
+        abortSignal: new AbortController().signal,
+      });
+      expect(result.returnDisplay).not.toContain('Blocked');
+    });
+
+    it('should allow PowerShell nested parentheses e.g. if ((condition))', async () => {
+      mockPlatform.mockReturnValue('win32');
+      mockShellExecutionService.mockImplementation((_cmd, _cwd, _callback) => ({
+        pid: 12345,
+        result: Promise.resolve({
+          output: 'result',
+          rawOutput: Buffer.from('result'),
+          exitCode: 0,
+          signal: null,
+          error: null,
+          aborted: false,
+          pid: 12345,
+          executionMethod: 'child_process',
+          backgrounded: false,
+        }),
+      }));
+      const tool = new ShellTool(mockConfig, createMockMessageBus());
+      const invocation = tool.build({
+        command: 'if ((condition)) { Write-Host ok }',
+      });
+      const result = await invocation.execute({
+        abortSignal: new AbortController().signal,
+      });
+      expect(result.returnDisplay).not.toContain('Blocked');
+    });
+  });
 });
diff --git a/packages/core/src/tools/shell.ts b/packages/core/src/tools/shell.ts
index a2cb44aba0..7be9a4f26f 100644
--- a/packages/core/src/tools/shell.ts
+++ b/packages/core/src/tools/shell.ts
@@ -40,6 +40,7 @@ import {
   stripShellWrapper,
   parseCommandDetails,
   hasRedirection,
+  detectCommandSubstitution,
   normalizeCommand,
   escapeShellArg,
 } from '../utils/shell-utils.js';
@@ -443,6 +444,18 @@ export class ShellToolInvocation extends BaseToolInvocation<
     } = options;
     const strippedCommand = stripShellWrapper(this.params.command);
 
+    if (detectCommandSubstitution(strippedCommand)) {
+      return {
+        llmContent:
+          'Command injection detected: command substitution syntax ' +
+          '($(), backticks, <() or >()) found in command arguments. ' +
+          'On PowerShell, @() array subexpressions and $() subexpressions are also blocked. ' +
+          'This is a security risk and the command was blocked.',
+        returnDisplay:
+          'Blocked: command substitution detected in shell command.',
+      };
+    }
+
     if (signal.aborted) {
       return {
         llmContent: 'Command was cancelled by user before it could start.',
diff --git a/packages/core/src/utils/shell-utils.ts b/packages/core/src/utils/shell-utils.ts
index 46cffa1d35..6f02579df9 100644
--- a/packages/core/src/utils/shell-utils.ts
+++ b/packages/core/src/utils/shell-utils.ts
@@ -1020,3 +1020,119 @@ export async function* execStreaming(
     prepared.cleanup?.();
   }
 }
+
+export function detectCommandSubstitution(command: string): boolean {
+  const shell = getShellConfiguration().shell;
+  const isPowerShell =
+    typeof shell === 'string' &&
+    (shell.toLowerCase().includes('powershell') ||
+      shell.toLowerCase().includes('pwsh'));
+  if (isPowerShell) {
+    return detectPowerShellSubstitution(command);
+  }
+  return detectBashSubstitution(command);
+}
+
+function detectBashSubstitution(command: string): boolean {
+  let inSingleQuote = false;
+  let inDoubleQuote = false;
+  let i = 0;
+  while (i < command.length) {
+    const char = command[i];
+    if (char === "'" && !inDoubleQuote) {
+      inSingleQuote = !inSingleQuote;
+      i++;
+      continue;
+    }
+    if (char === '"' && !inSingleQuote) {
+      inDoubleQuote = !inDoubleQuote;
+      i++;
+      continue;
+    }
+    if (inSingleQuote) {
+      i++;
+      continue;
+    }
+    if (char === '\\' && i + 1 < command.length) {
+      if (inDoubleQuote) {
+        const next = command[i + 1];
+        if (['$', '`', '"', '\\', '\n'].includes(next)) {
+          i += 2;
+          continue;
+        }
+      } else {
+        i += 2;
+        continue;
+      }
+    }
+    if (char === '$' && command[i + 1] === '(') {
+      return true;
+    }
+    if (
+      !inDoubleQuote &&
+      (char === '<' || char === '>') &&
+      command[i + 1] === '('
+    ) {
+      return true;
+    }
+    if (char === '`') {
+      return true;
+    }
+    i++;
+  }
+  return false;
+}
+
+const POWERSHELL_KEYWORD_RE =
+  /\b(if|elseif|else|foreach|for|while|do|switch|try|catch|finally|until|trap|function|filter)(\s+[-\w]+)*\s*$/i;
+
+function detectPowerShellSubstitution(command: string): boolean {
+  let inSingleQuote = false;
+  let inDoubleQuote = false;
+  let i = 0;
+  while (i < command.length) {
+    const char = command[i];
+
+    if (char === "'" && !inDoubleQuote) {
+      inSingleQuote = !inSingleQuote;
+      i++;
+      continue;
+    }
+    if (char === '"' && !inSingleQuote) {
+      inDoubleQuote = !inDoubleQuote;
+      i++;
+      continue;
+    }
+
+    if (inSingleQuote) {
+      i++;
+      continue;
+    }
+    if (char === '`' && i + 1 < command.length) {
+      i += 2;
+      continue;
+    }
+    if (char === '$' && command[i + 1] === '(') {
+      return true;
+    }
+    if (!inDoubleQuote && char === '@' && command[i + 1] === '(') {
+      return true;
+    }
+    if (!inDoubleQuote && char === '(') {
+      const before = command.slice(0, i).trimEnd();
+      const prevChar = before[before.length - 1];
+      if (prevChar === '(') {
+        i++;
+        continue;
+      }
+      if (POWERSHELL_KEYWORD_RE.test(before)) {
+        i++;
+        continue;
+      }
+      return true;
+    }
+
+    i++;
+  }
+  return false;
+}