Secure Code Warrior_.Net Core 資安練習_SQL Injection防範(一)

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問題描述

We received reports from a user that they were able to exploit a SQL Injection vulnerability in the transaction search feature of the internet bank solution. They stated that they were able to view transactions that belong to other users by exploiting this flaw, but pointed out that this vulnerability could allow an attacker to do all sorts of nasty stuff to the database, like dropping tables, viewing data from other tables, inserting data etc.

Please try to replicate what the user did, and show that you were able to exploit it by selecting transactions that belong to another account.



指示



1. View your account
Click the View button on the only account that appears in the list of bank accounts. This page lists transactions made on your account.







2. Observe the code
The View Account page offers a search functionality to search your transactions. If you take a look at the code snippet you can see how the database is queried for the transaction search. Take a special notice of how the searchTerm argument is appended to the raw sql query string.


舊程式碼(有資安問題)

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using System.Collections.Generic;
using System.Linq;
using Microsoft.EntityFrameworkCore;
using VikingBank.Data;

namespace VikingBank.Services
{
    public class TransactionService
    {
        private VikingBankContext _context;
        
        public TransactionService(VikingBankContext context)
        {
            _context = context;
        }
        
        public IEnumerable<Transaction> SearchTransactions(long accountId, string searchTerm)
        {


            var query = $"SELECT * FROM Transactions T WHERE T.ownerAccountId = {accountId}";
            if (!string.IsNullOrEmpty(searchTerm))
            {
                query += $" AND T.description LIKE '%{searchTerm}%'";
            }

            var transactionQuery = _context.Transactions.FromSqlRaw(query).Include(x => x.OwnerAccount).Include(x => x.ForeignAccount);

            return transactionQuery.ToList();
        }
    }
}





3. Enter a Search term
Try to enter something into the search term input field. Notice in the code snippet how the sql query string changes as you type. Submit a search to see the results, try different variations, e.g. try submitting the first three letters in one of your transactions' description to get a single result and try to submit a search term that doesn't match any description of your transactions.








4. Try to submit a single-quote
Now, submit a single quote ' into the search term input field. Notice the error that appears in the server log. The error message indicates that the SQL query that was executed was badly constructed. This tells us that the search term input was actually interpreted as being part of SQL query syntax instead of just being interpreted as being a pure value being queried. This means that the query is vulnerable to SQL Injection.


Exception when searching transactions, error: SQLite Error 1: 'unrecognized token: "' ) AS "v" LEFT JOIN "Accounts" AS "a" ON "v"."OwnerAccountId" = "a"."Id" LEFT JOIN "Accounts" AS "a0" ON "v"."ForeignAccountId" = "a0"."Id""'.



5. Submit the single-quote without getting the error
Now, submit again a single quote into the search term input field but add a whitespace and two dashes behind it, ' --. Notice that the error is now gone and you actually get some results back. This is because the two dashes are recognized as comment blocks in SQL, meaning that you comment out the rest of the query, i.e. the remaining single quote, hence your query is considered as being valid and will generate some results.




6. Select a transaction that doesn't belong to your account
Since we now know that the transaction search query is vulnerable to SQL Injection, we will exploit it by additionally selecting transactions that belong to another account, utilizing what we've just learned. Submit ' OR T.OwnerAccountId = 1 --, and notice a transaction that doesn't belong to your account appearing in the list. This is because you just manipulated the SQL query to select also transactions from account with Id 1.






===================================================================


字串串接SQL語句錯誤例子



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using System;
using System.Data;
using System.Data.SqlClient;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Identity;
using Microsoft.Extensions.Options;
using ToDoList.Settings;

namespace ToDoList.CustomProvider.Repositories
{
    public class UsersRepository : IUsersRepository
    {
        private readonly ConnectionStrings _connectionStrings;

        public UsersRepository(IOptions<ConnectionStrings> connectionStrings)
        {
            _connectionStrings = connectionStrings.Value;
        }

        public async Task<IdentityResult> CreateAsync(ApplicationUser user)
        {
            using (var connection = new SqlConnection(_connectionStrings.ToDoConnectionString))
            {
                connection.Open();
                using (var command = connection.CreateCommand())
                {
                    command.CommandText = @"
                    INSERT INTO [CustomUser]
                        ([Id],
                        [Email],
                        [EmailConfirmed],
                        [PasswordHash],
                        [UserName])
                    VALUES
                        (@id,
                        @email,
                        @emailConfirmed,
                        @passwordHash,
                        @userName)";

                    command.Parameters.Add("@id", SqlDbType.UniqueIdentifier).Value = user.Id;
                    command.Parameters.Add("@email", SqlDbType.NVarChar).Value = user.Email;
                    command.Parameters.Add("@emailConfirmed", SqlDbType.Bit).Value = user.EmailConfirmed;
                    command.Parameters.Add("@passwordHash", SqlDbType.NVarChar).Value = user.PasswordHash;
                    command.Parameters.Add("@userName", SqlDbType.NVarChar).Value = user.UserName;

                    var rows = await command.ExecuteNonQueryAsync();

                    return rows > 0
                        ? IdentityResult.Success
                        : IdentityResult.Failed(
                            new IdentityError {Description = $"Could not insert user {user.Email}."});
                }
            }
        }

        public async Task<IdentityResult> DeleteAsync(ApplicationUser user)
        {
            using (var connection = new SqlConnection(_connectionStrings.ToDoConnectionString))
            {
                connection.Open();
                using (var command = connection.CreateCommand())
                {
                    command.CommandText = @"DELETE FROM [CustomUser] WHERE [Id] = @id";

                    command.Parameters.Add("@id", SqlDbType.UniqueIdentifier).Value = user.Id;

                    var rows = await command.ExecuteNonQueryAsync();

                    return rows > 0
                        ? IdentityResult.Success
                        : IdentityResult.Failed(
                            new IdentityError {Description = $"Could not delete user {user.Email}."});
                }
            }
        }

        public async Task<ApplicationUser> FindByIdAsync(Guid userId)
        {
            ApplicationUser result = null;
            using (var connection = new SqlConnection(_connectionStrings.ToDoConnectionString))
            {
                connection.Open();
                using (var command = connection.CreateCommand())
                {
                    command.CommandText = @"SELECT TOP 1 * FROM [CustomUser] WHERE [Id] = @userId";
                    command.Parameters.Add("@userId", SqlDbType.UniqueIdentifier).Value = userId;

                    using (var reader = await command.ExecuteReaderAsync())
                    {
                        while (await reader.ReadAsync())
                        {
                            result = new ApplicationUser
                            {
                                Id = Guid.Parse(reader["Id"].ToString()),
                                Email = Convert.ToString(reader["Email"]),
                                EmailConfirmed = Convert.ToBoolean(reader["EmailConfirmed"]),
                                PasswordHash = Convert.ToString(reader["PasswordHash"]),
                                UserName = Convert.ToString(reader["UserName"])
                            };
                        }
                    }
                }
            }

            return result;
        }

        public async Task<ApplicationUser> FindByNameAsync(string userName)
        {
            ApplicationUser result = null;
            using (var connection = new SqlConnection(_connectionStrings.ToDoConnectionString))
            {
                connection.Open();
                using (var command = connection.CreateCommand())
                {
                    command.CommandText = $@"SELECT TOP 1 * FROM [CustomUser] WHERE [UserName] = {userName}";

                    using (var reader = await command.ExecuteReaderAsync())
                    {
                        while (await reader.ReadAsync())
                        {
                            result = new ApplicationUser
                            {
                                Id = Guid.Parse(reader["Id"].ToString()),
                                Email = Convert.ToString(reader["Email"]),
                                EmailConfirmed = Convert.ToBoolean(reader["EmailConfirmed"]),
                                PasswordHash = Convert.ToString(reader["PasswordHash"]),
                                UserName = Convert.ToString(reader["UserName"])
                            };
                        }
                    }
                }
            }

            return result;
        }
    }
}


解決方案1



(O)方案1程式碼-參數化帶入查詢->唯一正解

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public async Task<ApplicationUser> FindByNameAsync(string userName)
        {
            ApplicationUser result = null;
            using (var connection = new SqlConnection(_connectionStrings.ToDoConnectionString))
            {
                connection.Open();
                using (var command = connection.CreateCommand())
                {
                    command.CommandText = @"SELECT TOP 1 * FROM [CustomUser] WHERE [UserName] = @userName";
                    command.Parameters.Add("@userName", SqlDbType.NVarChar).Value = userName;

                    using (var reader = await command.ExecuteReaderAsync())
                    {
                        while (await reader.ReadAsync())
                        {
                            result = new ApplicationUser
                            {
                                Id = Guid.Parse(reader["Id"].ToString()),
                                Email = Convert.ToString(reader["Email"]),
                                EmailConfirmed = Convert.ToBoolean(reader["EmailConfirmed"]),
                                PasswordHash = Convert.ToString(reader["PasswordHash"]),
                                UserName = Convert.ToString(reader["UserName"])
                            };
                        }
                    }
                }
            }

            return result;
        }


方案2程式碼-過濾取代用戶端輸入的危險字元

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 public async Task<ApplicationUser> FindByNameAsync(string userName)
        {
            ApplicationUser result = null;
            using (var connection = new SqlConnection(_connectionStrings.ToDoConnectionString))
            {
                connection.Open();
                using (var command = connection.CreateCommand())
                {
                    command.CommandText = $@"SELECT TOP 1 * FROM [CustomUser] WHERE [UserName] = {ReplaceSpecialCharacters(userName)}";

                    using (var reader = await command.ExecuteReaderAsync())
                    {
                        while (await reader.ReadAsync())
                        {
                            result = new ApplicationUser
                            {
                                Id = Guid.Parse(reader["Id"].ToString()),
                                Email = Convert.ToString(reader["Email"]),
                                EmailConfirmed = Convert.ToBoolean(reader["EmailConfirmed"]),
                                PasswordHash = Convert.ToString(reader["PasswordHash"]),
                                UserName = Convert.ToString(reader["UserName"])
                            };
                        }
                    }
                }
            }

            return result;
        }
        
        private string ReplaceSpecialCharacters(string str)
        {
            var regex = new Regex("[*'/\",_&#^@]");
            var result = regex.Replace(str, string.Empty);
            return result;
        }


方案3程式碼-針對可能是進行異動竄改的指令進行取代

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        public async Task<ApplicationUser> FindByNameAsync(string userName)
        {
            ApplicationUser result = null;
            using (var connection = new SqlConnection(_connectionStrings.ToDoConnectionString))
            {
                connection.Open();
                using (var command = connection.CreateCommand())
                {
                    command.CommandText = $@"SELECT TOP 1 * FROM [CustomUser] WHERE [UserName] = {ReplaceSqlCommand(userName)}";

                    using (var reader = await command.ExecuteReaderAsync())
                    {
                        while (await reader.ReadAsync())
                        {
                            result = new ApplicationUser
                            {
                                Id = Guid.Parse(reader["Id"].ToString()),
                                Email = Convert.ToString(reader["Email"]),
                                EmailConfirmed = Convert.ToBoolean(reader["EmailConfirmed"]),
                                PasswordHash = Convert.ToString(reader["PasswordHash"]),
                                UserName = Convert.ToString(reader["UserName"])
                            };
                        }
                    }
                }
            }

            return result;
        }
        
        private string ReplaceSqlCommand(string str)
        {
            var result = str;
            var sqlCommands = new List<string>
            {
                "UPDATE",
                "DROP",
                "DELETE",
                "ALTER",
                "CREATE",
                "INSERT"
            };
            
            foreach(var command in sqlCommands)
            {
                result = result.Replace(command, "", StringComparison.InvariantCultureIgnoreCase);
            }

            return result;
        }


方案4程式碼-照已知的注入下法做取代防範


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        public async Task<ApplicationUser> FindByNameAsync(string userName)
        {
            ApplicationUser result = null;
            using (var connection = new SqlConnection(_connectionStrings.ToDoConnectionString))
            {
                connection.Open();
                using (var command = connection.CreateCommand())
                {
                    command.CommandText = $@"SELECT TOP 1 * FROM [CustomUser] WHERE [UserName] = {ReplaceExpression(userName)}";

                    using (var reader = await command.ExecuteReaderAsync())
                    {
                        while (await reader.ReadAsync())
                        {
                            result = new ApplicationUser
                            {
                                Id = Guid.Parse(reader["Id"].ToString()),
                                Email = Convert.ToString(reader["Email"]),
                                EmailConfirmed = Convert.ToBoolean(reader["EmailConfirmed"]),
                                PasswordHash = Convert.ToString(reader["PasswordHash"]),
                                UserName = Convert.ToString(reader["UserName"])
                            };
                        }
                    }
                }
            }

            return result;
        }
        
        
        private string ReplaceExpression(string str)
        {
            return str.Replace("OR '1'='1'", "", StringComparison.InvariantCultureIgnoreCase);
        }














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  若是出現 「必須」、「必需」、「...必...」、「應由」、「應先」、「應...」 則很高機率是圈 是非通常只要是如下字眼 「不必」+動詞 、「不需」「不須」、「可不」、「可以不」、「可立即」 有出現或符合的都選叉 (X)1.違規記點又不登記在駕照上，所以可以 不必理會 而任意違反交通規則。 (X)2.發生重大交通事故，為迅速恢復交通，清除現場，可 不必等待 肇事處理機關之指示，即可進行。 (X)3.道路駕駛練習，行車前 不必實施 車輛安全檢查，因為那是駕駛教練的工作。 (X)4.開車前， 不必檢查 機件安全，但在行駛中要隨時注意儀錶功能顯示，確保行車安全。 (X)5.煞車油若經常低於"MIN"線，只要添加即可， 不必到修理廠檢修 。 (X)6.冷卻系統只要副水箱在滿水位，主水箱 不必檢查 也不會有問題。 (X)7.引擎冷卻水內含有防凍液或防銹劑，可 不必更換 。 (X)8.儀錶板上的「燃油油量錶」之指針高度，已經降低至「E」點，橘色的「低油料警示燈」點亮時， 不必急著加油 ，到達目的地後再行補充燃油即可。 (X)9.有安全氣囊裝備的汽車， 不必繫 安全帶。 (X)10.煞車時有異音，是正常的情況， 不必檢修 。 (X)11.汽車定期檢驗 不必檢驗 車輛故障標誌，所以隨車不一定要帶車輛故障標誌。 (X)12.開車時 不必理會 義交之指揮，一切以號誌為主。 (X)13.汽車經過隧道，因隧道內燈光明亮視線良好，為省電可 不必開亮 頭燈。 (X)14.駕駛人只求技術優良，對遵守交通規則 不必太重視 。 (X)15.在開車前， 不必檢查 機件，以免耽誤行車時間。 (X)16.遇幼童專用車、校車、身心障礙者用特製車或教練車， 不必禮讓 。 (X)17.行車 不必攜帶 隨車工具。 (X)18.行車起駛前進， 不必顯示 方向燈。 (X)19.汽車通過鐵路平交道，前後兩車間， 不必保持 距離。 (X)20.夜間將車輛停放在無燈光設備及照明不清之道路時，亦 不必顯示 停車燈光或反光標識。 (X)21.在夜間或有霧靄、雨雪、風沙及晝晦時，把車輛停在路旁， 不必顯示 停車燈光或反光標識。 (X)22.汽車駕駛人，僅需具有優良駕駛技術， 不需 具備急救的常識和技能。 (X)23.汽車車身、引擎、底盤、電系等重要設備變更或調換時， 不需 向公路主管機關申請臨時檢驗。
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