feat(auth-validator): [Auth/PM-22975] Client Version Validator (#6588)

* feat(auth-validator): [PM-22975] Client Version Validator - Implementation.

* test(auth-validator): [PM-22975] Client Version Validator - Added tests.

src/Core/Context/ICurrentContext.cs

@@ -32,7 +32,7 @@ public interface ICurrentContext
     Guid? OrganizationId { get; set; }
     IdentityClientType IdentityClientType { get; set; }
     string ClientId { get; set; }
-    Version ClientVersion { get; set; }
+    Version? ClientVersion { get; set; }
     bool ClientVersionIsPrerelease { get; set; }
 
     Task BuildAsync(HttpContext httpContext, GlobalSettings globalSettings);

src/Core/Entities/User.cs

@@ -4,6 +4,7 @@ using Bit.Core.Auth.Enums;
 using Bit.Core.Auth.Models;
 using Bit.Core.Enums;
 using Bit.Core.KeyManagement.Models.Data;
+using Bit.Core.KeyManagement.Utilities;
 using Bit.Core.Utilities;
 using Microsoft.AspNetCore.Identity;
 
@@ -216,6 +217,42 @@ public class User : ITableObject<Guid>, IStorableSubscriber, IRevisable, ITwoFac
         return SecurityVersion ?? 1;
     }
 
+    /// <summary>
+    /// Evaluates user state to determine if they are currently in a v2 encryption state.
+    /// </summary>
+    /// <returns>If the shape of their private key is v2 as well as has the proper security version then true, otherwise false</returns>
+    public bool HasV2Encryption()
+    {
+        return HasV2KeyShape() && IsSecurityVersionTwo();
+    }
+
+    private bool HasV2KeyShape()
+    {
+        if (string.IsNullOrEmpty(PrivateKey))
+        {
+            return false;
+        }
+
+        try
+        {
+            return EncryptionParsing.GetEncryptionType(PrivateKey) == EncryptionType.XChaCha20Poly1305_B64;
+        }
+        catch (ArgumentException)
+        {
+            // Invalid encryption string format - treat as not v2
+            return false;
+        }
+    }
+
+    /// <summary>
+    /// This technically is correct but all versions after 1 are considered v2 encryption. Leaving for now with
+    /// KM's blessing that when a new version comes along they will handle migration.
+    /// </summary>
+    private bool IsSecurityVersionTwo()
+    {
+        return SecurityVersion == 2;
+    }
+
     /// <summary>
     /// Serializes the C# object to the User.TwoFactorProviders property in JSON format.
     /// </summary>

src/Core/Enums/EncryptionType.cs

@@ -11,8 +11,11 @@ public enum EncryptionType : byte
     XChaCha20Poly1305_B64 = 7,
 
     // asymmetric
+    [Obsolete("PM-29656 - Should probably be removed as it is not known to exist in the real world")]
     Rsa2048_OaepSha256_B64 = 3,
     Rsa2048_OaepSha1_B64 = 4,
+    [Obsolete("PM-29656 - Should probably be removed as it is not known to exist in the real world")]
     Rsa2048_OaepSha256_HmacSha256_B64 = 5,
+    [Obsolete("PM-29656 - Should probably be removed as it is not known to exist in the real world")]
     Rsa2048_OaepSha1_HmacSha256_B64 = 6
 }

src/Core/KeyManagement/Constants.cs

@@ -0,0 +1,6 @@
+namespace Bit.Core.KeyManagement;
+
+public static class Constants
+{
+    public static readonly Version MinimumClientVersionForV2Encryption = new("2025.11.0");
+}

src/Core/KeyManagement/UserKey/Implementations/RotateUserAccountKeysCommand.cs

@@ -6,6 +6,7 @@ using Bit.Core.Entities;
 using Bit.Core.Enums;
 using Bit.Core.KeyManagement.Models.Data;
 using Bit.Core.KeyManagement.Repositories;
+using Bit.Core.KeyManagement.Utilities;
 using Bit.Core.Platform.Push;
 using Bit.Core.Repositories;
 using Bit.Core.Services;
@@ -159,7 +160,7 @@ public class RotateUserAccountKeysCommand : IRotateUserAccountKeysCommand
         }
         else
         {
-            if (GetEncryptionType(model.AccountKeys.PublicKeyEncryptionKeyPairData.WrappedPrivateKey) != EncryptionType.AesCbc256_HmacSha256_B64)
+            if (EncryptionParsing.GetEncryptionType(model.AccountKeys.PublicKeyEncryptionKeyPairData.WrappedPrivateKey) != EncryptionType.AesCbc256_HmacSha256_B64)
             {
                 throw new InvalidOperationException("The provided account private key was not wrapped with AES-256-CBC-HMAC");
             }
@@ -231,7 +232,7 @@ public class RotateUserAccountKeysCommand : IRotateUserAccountKeysCommand
     {
         // Returns whether the user is a V2 user based on the private key's encryption type.
         ArgumentNullException.ThrowIfNull(user);
-        var isPrivateKeyEncryptionV2 = GetEncryptionType(user.PrivateKey) == EncryptionType.XChaCha20Poly1305_B64;
+        var isPrivateKeyEncryptionV2 = EncryptionParsing.GetEncryptionType(user.PrivateKey) == EncryptionType.XChaCha20Poly1305_B64;
         return isPrivateKeyEncryptionV2;
     }
 
@@ -259,7 +260,7 @@ public class RotateUserAccountKeysCommand : IRotateUserAccountKeysCommand
         {
             throw new InvalidOperationException("Signature key pair data is required for V2 encryption.");
         }
-        if (GetEncryptionType(model.AccountKeys.SignatureKeyPairData.WrappedSigningKey) != EncryptionType.XChaCha20Poly1305_B64)
+        if (EncryptionParsing.GetEncryptionType(model.AccountKeys.SignatureKeyPairData.WrappedSigningKey) != EncryptionType.XChaCha20Poly1305_B64)
         {
             throw new InvalidOperationException("The provided signing key data is not wrapped with XChaCha20-Poly1305.");
         }
@@ -268,7 +269,7 @@ public class RotateUserAccountKeysCommand : IRotateUserAccountKeysCommand
             throw new InvalidOperationException("The provided signature key pair data does not contain a valid verifying key.");
         }
 
-        if (GetEncryptionType(model.AccountKeys.PublicKeyEncryptionKeyPairData.WrappedPrivateKey) != EncryptionType.XChaCha20Poly1305_B64)
+        if (EncryptionParsing.GetEncryptionType(model.AccountKeys.PublicKeyEncryptionKeyPairData.WrappedPrivateKey) != EncryptionType.XChaCha20Poly1305_B64)
         {
             throw new InvalidOperationException("The provided private key encryption key is not wrapped with XChaCha20-Poly1305.");
         }
@@ -281,24 +282,4 @@ public class RotateUserAccountKeysCommand : IRotateUserAccountKeysCommand
             throw new InvalidOperationException("No signed security state provider for V2 user");
         }
     }
-
-    /// <summary>
-    /// Helper method to convert an encryption type string to an enum value.
-    /// </summary>
-    private static EncryptionType GetEncryptionType(string encString)
-    {
-        var parts = encString.Split('.');
-        if (parts.Length == 1)
-        {
-            throw new ArgumentException("Invalid encryption type string.");
-        }
-        if (byte.TryParse(parts[0], out var encryptionTypeNumber))
-        {
-            if (Enum.IsDefined(typeof(EncryptionType), encryptionTypeNumber))
-            {
-                return (EncryptionType)encryptionTypeNumber;
-            }
-        }
-        throw new ArgumentException("Invalid encryption type string.");
-    }
 }

src/Core/KeyManagement/Utilities/EncryptionParsing.cs

@@ -0,0 +1,28 @@
+using Bit.Core.Enums;
+
+namespace Bit.Core.KeyManagement.Utilities;
+
+public static class EncryptionParsing
+{
+    /// <summary>
+    /// Helper method to convert an encryption type string to an enum value.
+    /// </summary>
+    public static EncryptionType GetEncryptionType(string? encString)
+    {
+        ArgumentNullException.ThrowIfNull(encString);
+
+        var parts = encString.Split('.');
+        if (parts.Length == 1)
+        {
+            throw new ArgumentException("Invalid encryption type string.");
+        }
+        if (byte.TryParse(parts[0], out var encryptionTypeNumber))
+        {
+            if (Enum.IsDefined(typeof(EncryptionType), encryptionTypeNumber))
+            {
+                return (EncryptionType)encryptionTypeNumber;
+            }
+        }
+        throw new ArgumentException("Invalid encryption type string.");
+    }
+}

src/Identity/IdentityServer/RequestValidators/BaseRequestValidator.cs

@@ -40,6 +40,7 @@ public abstract class BaseRequestValidator<T> where T : class
     private readonly IUserRepository _userRepository;
     private readonly IAuthRequestRepository _authRequestRepository;
     private readonly IMailService _mailService;
+    private readonly IClientVersionValidator _clientVersionValidator;
 
     protected ICurrentContext CurrentContext { get; }
     protected IPolicyService PolicyService { get; }
@@ -69,7 +70,8 @@ public abstract class BaseRequestValidator<T> where T : class
         IPolicyRequirementQuery policyRequirementQuery,
         IAuthRequestRepository authRequestRepository,
         IMailService mailService,
-        IUserAccountKeysQuery userAccountKeysQuery
+        IUserAccountKeysQuery userAccountKeysQuery,
+        IClientVersionValidator clientVersionValidator
     )
     {
         _userManager = userManager;
@@ -91,6 +93,7 @@ public abstract class BaseRequestValidator<T> where T : class
         _authRequestRepository = authRequestRepository;
         _mailService = mailService;
         _accountKeysQuery = userAccountKeysQuery;
+        _clientVersionValidator = clientVersionValidator;
     }
 
     protected async Task ValidateAsync(T context, ValidatedTokenRequest request,
@@ -135,7 +138,13 @@ public abstract class BaseRequestValidator<T> where T : class
             // validation to perform the recovery as part of scheme validation based on the request.
             return
             [
-                () => ValidateMasterPasswordAsync(context, validatorContext),
+                () => ValidateGrantSpecificContext(context, validatorContext),
+                // Now check the version number of the client. Do this after ValidateContextAsync so that
+                // we prevent account enumeration. If we were to do this before ValidateContextAsync, then attackers
+                // could use a known invalid client version and make a request for a user (before we know if they have
+                // demonstrated ownership of the account via correct credentials) and identify if they exist by getting
+                // an error response back from the validator saying the user is not compatible with the client.
+                () => ValidateClientVersionAsync(context, validatorContext),
                 () => ValidateTwoFactorAsync(context, request, validatorContext),
                 () => ValidateSsoAsync(context, request, validatorContext),
                 () => ValidateNewDeviceAsync(context, request, validatorContext),
@@ -148,7 +157,13 @@ public abstract class BaseRequestValidator<T> where T : class
             // The typical validation scenario.
             return
             [
-                () => ValidateMasterPasswordAsync(context, validatorContext),
+                () => ValidateGrantSpecificContext(context, validatorContext),
+                // Now check the version number of the client. Do this after ValidateContextAsync so that
+                // we prevent account enumeration. If we were to do this before ValidateContextAsync, then attackers
+                // could use a known invalid client version and make a request for a user (before we know if they have
+                // demonstrated ownership of the account via correct credentials) and identify if they exist by getting
+                // an error response back from the validator saying the user is not compatible with the client.
+                () => ValidateClientVersionAsync(context, validatorContext),
                 () => ValidateSsoAsync(context, request, validatorContext),
                 () => ValidateTwoFactorAsync(context, request, validatorContext),
                 () => ValidateNewDeviceAsync(context, request, validatorContext),
@@ -201,12 +216,29 @@ public abstract class BaseRequestValidator<T> where T : class
     }
 
     /// <summary>
-    /// Validates the user's Master Password hash.
+    /// Validates whether the client version is compatible for the user attempting to authenticate.
+    /// </summary>
+    /// <returns>true if the scheme successfully passed validation, otherwise false.</returns>
+    private async Task<bool> ValidateClientVersionAsync(T context, CustomValidatorRequestContext validatorContext)
+    {
+        var ok = _clientVersionValidator.Validate(validatorContext.User, validatorContext);
+        if (ok)
+        {
+            return true;
+        }
+
+        SetValidationErrorResult(context, validatorContext);
+        await LogFailedLoginEvent(validatorContext.User, EventType.User_FailedLogIn);
+        return false;
+    }
+
+    /// <summary>
+    /// Validates the user's master password, webauthen, or custom token request via the appropriate context validator.
     /// </summary>
     /// <param name="context">The current request context.</param>
     /// <param name="validatorContext"><see cref="Bit.Identity.IdentityServer.CustomValidatorRequestContext" /></param>
     /// <returns>true if the scheme successfully passed validation, otherwise false.</returns>
-    private async Task<bool> ValidateMasterPasswordAsync(T context, CustomValidatorRequestContext validatorContext)
+    private async Task<bool> ValidateGrantSpecificContext(T context, CustomValidatorRequestContext validatorContext)
     {
         var valid = await ValidateContextAsync(context, validatorContext);
         var user = validatorContext.User;

src/Identity/IdentityServer/RequestValidators/ClientVersionValidator.cs

@@ -0,0 +1,92 @@
+using Bit.Core.Context;
+using Bit.Core.Entities;
+using Bit.Core.KeyManagement;
+using Bit.Core.Models.Api;
+using Duende.IdentityServer.Validation;
+
+namespace Bit.Identity.IdentityServer.RequestValidators;
+
+public interface IClientVersionValidator
+{
+    bool Validate(User user, CustomValidatorRequestContext requestContext);
+}
+
+/// <summary>
+/// This validator will use the Client Version on a request, which currently maps
+/// to the "Bitwarden-Client-Version" header, to determine if a user meets minimum
+/// required client version for issuing tokens on an old client. This is done to
+/// incentivize users to get on an updated client when their password encryption
+/// method has already been updated.
+///
+/// If the header is omitted, then the validator returns that this request is invalid.
+/// </summary>
+public class ClientVersionValidator(
+    ICurrentContext currentContext)
+    : IClientVersionValidator
+{
+    private const string _upgradeMessage = "Please update your app to continue using Bitwarden";
+    private const string _noUserMessage = "No user found while trying to validate client version";
+    private const string _versionHeaderMissing = "No client version header found, required to prevent encryption errors. Please confirm your client is supplying the header: \"Bitwarden-Client-Version\"";
+
+    public bool Validate(User? user, CustomValidatorRequestContext requestContext)
+    {
+        // Do this nullish check because the base request validator currently is not
+        // strict null checking. Once that gets fixed then we can see about making
+        // the user not nullish checked. If they are null then the validator should fail.
+        if (user == null)
+        {
+            FillRequestContextWithErrorData(requestContext, "no_user", _noUserMessage);
+            return false;
+        }
+
+        Version? clientVersion = currentContext.ClientVersion;
+
+        // Deny access if the client version headers are missing.
+        // We want to establish a strict contract with clients that if they omit this header,
+        // then the server cannot guarantee that a client won't do harm to a user's data
+        // with stale encryption architecture.
+        if (clientVersion == null)
+        {
+            FillRequestContextWithErrorData(requestContext, "version_header_missing", _versionHeaderMissing);
+            return false;
+        }
+
+        // Determine the minimum version client that a user needs. If no V2 encryption detected then
+        // no validation needs to occur, which is why min version number can be null.
+        Version? minVersion = user.HasV2Encryption() ? Constants.MinimumClientVersionForV2Encryption : null;
+
+        // If min version is null then we know that the user had an encryption
+        // configuration that doesn't require a minimum version. Allowing through.
+        if (minVersion == null)
+        {
+            return true;
+        }
+
+        if (clientVersion < minVersion)
+        {
+            FillRequestContextWithErrorData(requestContext, "invalid_client_version", _upgradeMessage);
+            return false;
+        }
+
+        return true;
+    }
+
+    private void FillRequestContextWithErrorData(
+        CustomValidatorRequestContext requestContext,
+        string errorId,
+        string errorMessage)
+    {
+        requestContext.ValidationErrorResult = new ValidationResult
+        {
+            Error = errorId,
+            ErrorDescription = errorMessage,
+            IsError = true
+        };
+        requestContext.CustomResponse = new Dictionary<string, object>
+        {
+            { "ErrorModel", new ErrorResponseModel(errorMessage) }
+        };
+    }
+}
+
+

src/Identity/IdentityServer/RequestValidators/CustomTokenRequestValidator.cs

@@ -16,11 +16,8 @@ using Bit.Core.Settings;
 using Duende.IdentityModel;
 using Duende.IdentityServer.Extensions;
 using Duende.IdentityServer.Validation;
-using HandlebarsDotNet;
 using Microsoft.AspNetCore.Identity;
 
-#nullable enable
-
 namespace Bit.Identity.IdentityServer.RequestValidators;
 
 public class CustomTokenRequestValidator : BaseRequestValidator<CustomTokenRequestValidationContext>,
@@ -50,7 +47,8 @@ public class CustomTokenRequestValidator : BaseRequestValidator<CustomTokenReque
         IPolicyRequirementQuery policyRequirementQuery,
         IAuthRequestRepository authRequestRepository,
         IMailService mailService,
-        IUserAccountKeysQuery userAccountKeysQuery)
+        IUserAccountKeysQuery userAccountKeysQuery,
+        IClientVersionValidator clientVersionValidator)
         : base(
             userManager,
             userService,
@@ -70,7 +68,8 @@ public class CustomTokenRequestValidator : BaseRequestValidator<CustomTokenReque
             policyRequirementQuery,
             authRequestRepository,
             mailService,
-            userAccountKeysQuery)
+            userAccountKeysQuery,
+            clientVersionValidator)
     {
         _userManager = userManager;
         _updateInstallationCommand = updateInstallationCommand;

src/Identity/IdentityServer/RequestValidators/ResourceOwnerPasswordValidator.cs

@@ -44,7 +44,8 @@ public class ResourceOwnerPasswordValidator : BaseRequestValidator<ResourceOwner
         IUserDecryptionOptionsBuilder userDecryptionOptionsBuilder,
         IPolicyRequirementQuery policyRequirementQuery,
         IMailService mailService,
-        IUserAccountKeysQuery userAccountKeysQuery)
+        IUserAccountKeysQuery userAccountKeysQuery,
+        IClientVersionValidator clientVersionValidator)
         : base(
             userManager,
             userService,
@@ -64,7 +65,8 @@ public class ResourceOwnerPasswordValidator : BaseRequestValidator<ResourceOwner
             policyRequirementQuery,
             authRequestRepository,
             mailService,
-            userAccountKeysQuery)
+            userAccountKeysQuery,
+            clientVersionValidator)
     {
         _userManager = userManager;
         _currentContext = currentContext;
@@ -74,7 +76,6 @@ public class ResourceOwnerPasswordValidator : BaseRequestValidator<ResourceOwner
 
     public async Task ValidateAsync(ResourceOwnerPasswordValidationContext context)
     {
-
         var user = await _userManager.FindByEmailAsync(context.UserName.ToLowerInvariant());
         // We want to keep this device around incase the device is new for the user
         var requestDevice = DeviceValidator.GetDeviceFromRequest(context.Request);

src/Identity/IdentityServer/RequestValidators/WebAuthnGrantValidator.cs

@@ -53,7 +53,8 @@ public class WebAuthnGrantValidator : BaseRequestValidator<ExtensionGrantValidat
         IPolicyRequirementQuery policyRequirementQuery,
         IAuthRequestRepository authRequestRepository,
         IMailService mailService,
-        IUserAccountKeysQuery userAccountKeysQuery)
+        IUserAccountKeysQuery userAccountKeysQuery,
+        IClientVersionValidator clientVersionValidator)
         : base(
             userManager,
             userService,
@@ -73,7 +74,8 @@ public class WebAuthnGrantValidator : BaseRequestValidator<ExtensionGrantValidat
             policyRequirementQuery,
             authRequestRepository,
             mailService,
-            userAccountKeysQuery)
+            userAccountKeysQuery,
+            clientVersionValidator)
     {
         _assertionOptionsDataProtector = assertionOptionsDataProtector;
         _assertWebAuthnLoginCredentialCommand = assertWebAuthnLoginCredentialCommand;

src/Identity/Utilities/ServiceCollectionExtensions.cs

@@ -25,6 +25,7 @@ public static class ServiceCollectionExtensions
         services.AddTransient<IAuthorizationCodeStore, AuthorizationCodeStore>();
         services.AddTransient<IUserDecryptionOptionsBuilder, UserDecryptionOptionsBuilder>();
         services.AddTransient<IDeviceValidator, DeviceValidator>();
+        services.AddTransient<IClientVersionValidator, ClientVersionValidator>();
         services.AddTransient<ITwoFactorAuthenticationValidator, TwoFactorAuthenticationValidator>();
         services.AddTransient<ISsoRequestValidator, SsoRequestValidator>();
         services.AddTransient<ILoginApprovingClientTypes, LoginApprovingClientTypes>();

src/SharedWeb/Utilities/ServiceCollectionExtensions.cs

@@ -6,7 +6,6 @@ using System.Reflection;
 using System.Security.Claims;
 using System.Security.Cryptography.X509Certificates;
 using AspNetCoreRateLimit;
-using Bit.Core;
 using Bit.Core.AdminConsole.AbilitiesCache;
 using Bit.Core.AdminConsole.Models.Business.Tokenables;
 using Bit.Core.AdminConsole.OrganizationFeatures.Policies;
@@ -83,6 +82,7 @@ using Microsoft.Extensions.Options;
 using Microsoft.OpenApi;
 using StackExchange.Redis;
 using Swashbuckle.AspNetCore.SwaggerGen;
+using Constants = Bit.Core.Constants;
 using NoopRepos = Bit.Core.Repositories.Noop;
 using Role = Bit.Core.Entities.Role;
 using TableStorageRepos = Bit.Core.Repositories.TableStorage;