diff --git a/packages/mcp-provider-dx-core/src/shared/soqlUtils.ts b/packages/mcp-provider-dx-core/src/shared/soqlUtils.ts
new file mode 100644
index 00000000..32c4cfd4
--- /dev/null
+++ b/packages/mcp-provider-dx-core/src/shared/soqlUtils.ts
@@ -0,0 +1,88 @@
+/**
+ * Utility functions for safe SOQL query construction
+ */
+
+/**
+ * Escapes single quotes in a string for use in SOQL queries.
+ */
+export function escapeSoqlString(value: string): string {
+    if (typeof value !== 'string') {
+        throw new Error('SOQL escape requires string input');
+    }
+    // Escape single quotes by doubling them (SOQL standard)
+    return value.replace(/'/g, "\\'");
+}
+
+/**
+ * Checks if a string contains potential SQL injection patterns.
+ * Returns true if injection patterns are detected.
+ */
+export function containsSqlInjectionPatterns(value: string): boolean {
+    if (typeof value !== 'string') {
+        return true;
+    }
+
+    const trimmed = value.trim();
+
+    // Check for common SQL injection patterns
+    const injectionPatterns = [
+        /--/,           // SQL comment
+        /;/,            // Statement terminator
+        /\bOR\b/i,      // OR keyword
+        /\bAND\b/i,     // AND keyword
+        /\bUNION\b/i,   // UNION keyword
+        /\bSELECT\b/i,  // SELECT keyword
+        /\bDROP\b/i,    // DROP keyword
+        /\bINSERT\b/i,  // INSERT keyword
+        /\bUPDATE\b/i,  // UPDATE keyword
+        /\bDELETE\b/i,  // DELETE keyword
+        /\bEXEC\b/i,    // EXEC keyword
+    ];
+
+    // Check for injection patterns (excluding the single quote check since we'll escape those)
+    return injectionPatterns.some(pattern => pattern.test(trimmed));
+}
+
+/**
+ * Validates a Salesforce username format.
+ * Must contain @ and follow email-like format without injection patterns.
+ */
+export function isValidUsername(username: string): boolean {
+    if (typeof username !== 'string') {
+        return false;
+    }
+
+    const trimmed = username.trim();
+
+    // Must contain @
+    if (!trimmed.includes('@')) {
+        return false;
+    }
+
+    // Basic email format: something@something.something
+    const emailPattern = /^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$/;
+    if (!emailPattern.test(trimmed)) {
+        return false;
+    }
+
+    // Check for SQL injection patterns
+    if (containsSqlInjectionPatterns(trimmed)) {
+        return false;
+    }
+
+    return true;
+}
+
+/**
+ * Validates and escapes a Salesforce username for SOQL queries.
+ * Throws an error if the username format is invalid or contains injection attempts.
+ */
+export function validateAndEscapeUsername(username: string): string {
+    const trimmed = username.trim();
+
+    if (!isValidUsername(trimmed)) {
+        throw new Error(`Invalid username format or potential SQL injection detected: ${username}`);
+    }
+
+    return escapeSoqlString(trimmed);
+}
diff --git a/packages/mcp-provider-dx-core/src/tools/assign_permission_set.ts b/packages/mcp-provider-dx-core/src/tools/assign_permission_set.ts
index d55cba96..0e741a6e 100644
--- a/packages/mcp-provider-dx-core/src/tools/assign_permission_set.ts
+++ b/packages/mcp-provider-dx-core/src/tools/assign_permission_set.ts
@@ -20,6 +20,7 @@ import { McpTool, McpToolConfig, ReleaseState, Services, Toolset } from '@salesf
 import { CallToolResult } from '@modelcontextprotocol/sdk/types.js';
 import { directoryParam, usernameOrAliasParam } from '../shared/params.js';
 import { textResponse } from '../shared/utils.js';
+import { validateAndEscapeUsername } from '../shared/soqlUtils.js';
 
 /*
  * Assign permission set
@@ -117,10 +118,21 @@ export class AssignPermissionSetMcpTool extends McpTool<InputArgsShape, OutputAr
         return textResponse('Unable to resolve the username for alias. Make sure it is correct', true);
       }
 
+      // Validate and escape the username to prevent SOQL injection
+      let validatedUsername: string;
+      try {
+        validatedUsername = validateAndEscapeUsername(assignTo);
+      } catch (error) {
+        return textResponse(
+          `Invalid username format: ${error instanceof Error ? error.message : 'Unknown error'}`,
+          true,
+        );
+      }
+
       const org = await Org.create({ connection });
       const user = await User.create({ org });
       const queryResult = await connection.singleRecordQuery<{ Id: string }>(
-        `SELECT Id FROM User WHERE Username='${assignTo}'`,
+        `SELECT Id FROM User WHERE Username='${validatedUsername}'`,
       );
 
       await user.assignPermissionSets(queryResult.Id, [input.permissionSetName]);
diff --git a/packages/mcp-provider-dx-core/test/shared/soqlUtils.test.ts b/packages/mcp-provider-dx-core/test/shared/soqlUtils.test.ts
new file mode 100644
index 00000000..8ab69003
--- /dev/null
+++ b/packages/mcp-provider-dx-core/test/shared/soqlUtils.test.ts
@@ -0,0 +1,155 @@
+import { expect } from 'chai';
+import {
+    escapeSoqlString,
+    containsSqlInjectionPatterns,
+    isValidUsername,
+    validateAndEscapeUsername
+} from '../../src/shared/soqlUtils.js';
+
+describe('soqlUtils', () => {
+    describe('escapeSoqlString', () => {
+        it('should escape single quotes', () => {
+            expect(escapeSoqlString("O'Brien")).to.equal("O\\'Brien");
+            expect(escapeSoqlString("It's working")).to.equal("It\\'s working");
+        });
+
+        it('should handle strings without quotes', () => {
+            expect(escapeSoqlString("normal text")).to.equal("normal text");
+        });
+
+        it('should handle empty strings', () => {
+            expect(escapeSoqlString("")).to.equal("");
+        });
+
+        it('should throw on non-string values', () => {
+            expect(() => escapeSoqlString(null as any)).to.throw();
+            expect(() => escapeSoqlString(123 as any)).to.throw();
+        });
+    });
+
+    describe('containsSqlInjectionPatterns', () => {
+        it('should detect SQL injection patterns', () => {
+            expect(containsSqlInjectionPatterns("' OR '1'='1")).to.be.true;
+            expect(containsSqlInjectionPatterns("'; DROP TABLE--")).to.be.true;
+            expect(containsSqlInjectionPatterns("test UNION SELECT")).to.be.true;
+            expect(containsSqlInjectionPatterns("value--comment")).to.be.true;
+            expect(containsSqlInjectionPatterns("item; DELETE FROM")).to.be.true;
+        });
+
+        it('should allow safe strings', () => {
+            expect(containsSqlInjectionPatterns("user@example.com")).to.be.false;
+            expect(containsSqlInjectionPatterns("admin@test.org")).to.be.false;
+            expect(containsSqlInjectionPatterns("test.user@company.com")).to.be.false;
+        });
+
+        it('should handle non-string values', () => {
+            expect(containsSqlInjectionPatterns(null as any)).to.be.true;
+            expect(containsSqlInjectionPatterns(undefined as any)).to.be.true;
+            expect(containsSqlInjectionPatterns(123 as any)).to.be.true;
+        });
+    });
+
+    describe('isValidUsername', () => {
+        it('should accept valid email-like usernames', () => {
+            expect(isValidUsername('user@example.com')).to.be.true;
+            expect(isValidUsername('test.user@company.org')).to.be.true;
+            expect(isValidUsername('admin+test@domain.co.uk')).to.be.true;
+            expect(isValidUsername('user_name@sub.domain.com')).to.be.true;
+        });
+
+        it('should reject usernames without @', () => {
+            expect(isValidUsername('username')).to.be.false;
+            expect(isValidUsername('admin')).to.be.false;
+        });
+
+        it('should reject invalid email formats', () => {
+            expect(isValidUsername('@example.com')).to.be.false;
+            expect(isValidUsername('user@')).to.be.false;
+            expect(isValidUsername('user@domain')).to.be.false;
+            expect(isValidUsername('user@@domain.com')).to.be.false;
+        });
+
+        it('should reject SQL injection attempts', () => {
+            expect(isValidUsername("user@example.com' OR 1=1--")).to.be.false;
+            expect(isValidUsername("x@example.com' OR IsActive = true OR Username='x")).to.be.false;
+            expect(isValidUsername("admin@test.com; DROP TABLE")).to.be.false;
+            expect(isValidUsername("user@domain.com' UNION SELECT")).to.be.false;
+        });
+
+        it('should reject non-string values', () => {
+            expect(isValidUsername(null as any)).to.be.false;
+            expect(isValidUsername(undefined as any)).to.be.false;
+            expect(isValidUsername(123 as any)).to.be.false;
+        });
+    });
+
+    describe('validateAndEscapeUsername', () => {
+        it('should return escaped valid usernames', () => {
+            expect(validateAndEscapeUsername('user@example.com')).to.equal('user@example.com');
+            expect(validateAndEscapeUsername(' admin@test.org ')).to.equal('admin@test.org');
+            expect(validateAndEscapeUsername('test.user@company.com')).to.equal('test.user@company.com');
+        });
+
+        it('should escape single quotes in valid usernames', () => {
+            expect(validateAndEscapeUsername("o'brien@example.com")).to.equal("o\\'brien@example.com");
+        });
+
+        it('should throw on invalid usernames', () => {
+            expect(() => validateAndEscapeUsername('invalid')).to.throw(/Invalid username format/);
+            expect(() => validateAndEscapeUsername('user@')).to.throw(/Invalid username format/);
+            expect(() => validateAndEscapeUsername('@domain.com')).to.throw(/Invalid username format/);
+        });
+
+        it('should throw on SQL injection attempts', () => {
+            expect(() => validateAndEscapeUsername("user@example.com' OR 1=1--")).to.throw(/SQL injection/);
+            expect(() => validateAndEscapeUsername("x@example.com' OR IsActive = true OR Username='x")).to.throw(/SQL injection/);
+            expect(() => validateAndEscapeUsername("admin@test.com; DROP TABLE")).to.throw(/SQL injection/);
+        });
+
+        it('should reject the proof of concept from the bug report', () => {
+            const pocUsername = "x@example.com' OR IsActive = true OR Username='x";
+            expect(() => validateAndEscapeUsername(pocUsername)).to.throw(/SQL injection/);
+        });
+    });
+
+    describe('Security - Prevent injection from bug W-22550508', () => {
+        it('should block the exact proof of concept attack', () => {
+            // From the bug report:
+            // "onBehalfOf": "x@example.com' OR IsActive = true OR Username='x"
+            const attackUsername = "x@example.com' OR IsActive = true OR Username='x";
+
+            // Should be detected as invalid
+            expect(isValidUsername(attackUsername)).to.be.false;
+
+            // Should throw when trying to validate
+            expect(() => validateAndEscapeUsername(attackUsername)).to.throw();
+        });
+
+        it('should allow legitimate usernames', () => {
+            const legitimateUsernames = [
+                'authorized-org-admin@example.com',
+                'test-user@company.org',
+                'admin+alias@domain.co.uk'
+            ];
+
+            legitimateUsernames.forEach(username => {
+                expect(isValidUsername(username), `Should accept: ${username}`).to.be.true;
+                expect(() => validateAndEscapeUsername(username)).to.not.throw();
+            });
+        });
+
+        it('should prevent predicate modification via various injection techniques', () => {
+            const injectionAttempts = [
+                "user@test.com' OR 1=1--",
+                "admin@test.com'; DROP TABLE Users--",
+                "user@test.com' UNION SELECT * FROM User--",
+                "test@example.com' AND '1'='1",
+                "user@test.com' OR IsActive=true--"
+            ];
+
+            injectionAttempts.forEach(attempt => {
+                expect(() => validateAndEscapeUsername(attempt), `Should reject: ${attempt}`).to.throw();
+            });
+        });
+    });
+});