diff --git a/src/Api/AdminConsole/Models/Request/OrganizationDomainRequestModel.cs b/src/Api/AdminConsole/Models/Request/OrganizationDomainRequestModel.cs
index 46b253da31..3a2ada719f 100644
--- a/src/Api/AdminConsole/Models/Request/OrganizationDomainRequestModel.cs
+++ b/src/Api/AdminConsole/Models/Request/OrganizationDomainRequestModel.cs
@@ -2,11 +2,13 @@
 #nullable disable
 
 using System.ComponentModel.DataAnnotations;
+using Bit.Core.Utilities;
 
 namespace Bit.Api.AdminConsole.Models.Request;
 
 public class OrganizationDomainRequestModel
 {
     [Required]
+    [DomainNameValidator]
     public string DomainName { get; set; }
 }
diff --git a/src/Core/Utilities/DomainNameAttribute.cs b/src/Core/Utilities/DomainNameAttribute.cs
new file mode 100644
index 0000000000..9b571e96d7
--- /dev/null
+++ b/src/Core/Utilities/DomainNameAttribute.cs
@@ -0,0 +1,64 @@
+using System.ComponentModel.DataAnnotations;
+using System.Text.RegularExpressions;
+
+namespace Bit.Core.Utilities;
+
+/// <summary>
+/// https://bitwarden.atlassian.net/browse/VULN-376
+/// Domain names are vulnerable to XSS attacks if not properly validated.
+/// Domain names can contain letters, numbers, dots, and hyphens.
+/// Domain names maybe internationalized (IDN) and contain unicode characters.
+/// </summary>
+public class DomainNameValidatorAttribute : ValidationAttribute
+{
+    // RFC 1123 compliant domain name regex
+    // - Allows alphanumeric characters and hyphens
+    // - Cannot start or end with a hyphen
+    // - Each label (part between dots) must be 1-63 characters
+    // - Total length should not exceed 253 characters
+    // - Supports internationalized domain names (IDN) - which is why this regex includes unicode ranges
+    private static readonly Regex _domainNameRegex = new(
+        @"^(?:[a-zA-Z0-9\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF](?:[a-zA-Z0-9\-\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF]{0,61}[a-zA-Z0-9\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])?\.)*[a-zA-Z0-9\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF](?:[a-zA-Z0-9\-\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF]{0,61}[a-zA-Z0-9\u00A0-\uD7FF\uF900-\uFDCF\uFDF0-\uFFEF])?$",
+        RegexOptions.Compiled | RegexOptions.IgnoreCase
+    );
+
+    public DomainNameValidatorAttribute()
+        : base("The {0} field is not a valid domain name.")
+    { }
+
+    public override bool IsValid(object? value)
+    {
+        if (value == null)
+        {
+            return true; // Use [Required] for null checks
+        }
+
+        var domainName = value.ToString();
+
+        if (string.IsNullOrWhiteSpace(domainName))
+        {
+            return false;
+        }
+
+        // Reject if contains any whitespace (including leading/trailing spaces, tabs, newlines)
+        if (domainName.Any(char.IsWhiteSpace))
+        {
+            return false;
+        }
+
+        // Check length constraints
+        if (domainName.Length > 253)
+        {
+            return false;
+        }
+
+        // Check for control characters or other dangerous characters
+        if (domainName.Any(c => char.IsControl(c) || c == '<' || c == '>' || c == '"' || c == '\'' || c == '&'))
+        {
+            return false;
+        }
+
+        // Validate against domain name regex
+        return _domainNameRegex.IsMatch(domainName);
+    }
+}
diff --git a/test/Core.Test/Utilities/DomainNameAttributeTests.cs b/test/Core.Test/Utilities/DomainNameAttributeTests.cs
new file mode 100644
index 0000000000..3f3190c9a1
--- /dev/null
+++ b/test/Core.Test/Utilities/DomainNameAttributeTests.cs
@@ -0,0 +1,84 @@
+using Bit.Core.Utilities;
+using Xunit;
+
+namespace Bit.Core.Test.Utilities;
+
+public class DomainNameValidatorAttributeTests
+{
+    [Theory]
+    [InlineData("example.com")]                     // basic domain
+    [InlineData("sub.example.com")]                 // subdomain
+    [InlineData("sub.sub2.example.com")]            // multiple subdomains
+    [InlineData("example-dash.com")]                // domain with dash
+    [InlineData("123example.com")]                  // domain starting with number
+    [InlineData("example123.com")]                  // domain with numbers
+    [InlineData("e.com")]                           // short domain
+    [InlineData("very-long-subdomain-name.example.com")]  // long subdomain
+    [InlineData("wörldé.com")]                      // unicode domain (IDN)
+    public void IsValid_ReturnsTrueWhenValid(string domainName)
+    {
+        var sut = new DomainNameValidatorAttribute();
+
+        var actual = sut.IsValid(domainName);
+
+        Assert.True(actual);
+    }
+
+    [Theory]
+    [InlineData("<script>alert('xss')</script>")]   // XSS attempt
+    [InlineData("example.com<script>")]             // XSS suffix
+    [InlineData("<img src=x>")]                     // HTML tag
+    [InlineData("example.com\t")]                   // trailing tab
+    [InlineData("\texample.com")]                   // leading tab
+    [InlineData("exam\tple.com")]                   // middle tab
+    [InlineData("example.com\n")]                   // newline
+    [InlineData("example.com\r")]                   // carriage return
+    [InlineData("example.com\b")]                   // backspace
+    [InlineData("exam ple.com")]                    // space in domain
+    [InlineData("example.com ")]                    // trailing space (after trim, becomes valid, but with space it's invalid)
+    [InlineData(" example.com")]                    // leading space (after trim, becomes valid, but with space it's invalid)
+    [InlineData("example&.com")]                    // ampersand
+    [InlineData("example'.com")]                    // single quote
+    [InlineData("example\".com")]                   // double quote
+    [InlineData(".example.com")]                    // starts with dot
+    [InlineData("example.com.")]                    // ends with dot
+    [InlineData("example..com")]                    // double dot
+    [InlineData("-example.com")]                    // starts with dash
+    [InlineData("example-.com")]                    // label ends with dash
+    [InlineData("")]                                // empty string
+    [InlineData("   ")]                             // whitespace only
+    [InlineData("http://example.com")]              // URL scheme
+    [InlineData("example.com/path")]                // path component
+    [InlineData("user@example.com")]                // email format
+    public void IsValid_ReturnsFalseWhenInvalid(string domainName)
+    {
+        var sut = new DomainNameValidatorAttribute();
+
+        var actual = sut.IsValid(domainName);
+
+        Assert.False(actual);
+    }
+
+    [Fact]
+    public void IsValid_ReturnsTrueWhenNull()
+    {
+        var sut = new DomainNameValidatorAttribute();
+
+        var actual = sut.IsValid(null);
+
+        // Null validation should be handled by [Required] attribute
+        Assert.True(actual);
+    }
+
+    [Fact]
+    public void IsValid_ReturnsFalseWhenTooLong()
+    {
+        var sut = new DomainNameValidatorAttribute();
+        // Create a domain name longer than 253 characters
+        var longDomain = new string('a', 250) + ".com";
+
+        var actual = sut.IsValid(longDomain);
+
+        Assert.False(actual);
+    }
+}