CVE-2021-3646 (published 2021-09-10T18:15Z)

btcpayserver is vulnerable to Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Severity: MEDIUM
CVSS v2 base score: 4.3 (AV:N/AC:M/Au:N/C:N/I:P/A:N)
CVSS v3 base score: 6.1, MEDIUM (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N)

Weakness information:
cwe_id: CWE-79
cwe_name: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
description: The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.
extended_description: 
            Cross-site scripting (XSS) vulnerabilities occur when:
            
               Untrusted data enters a web application, typically from a web request.
               The web application dynamically generates a web page that contains this untrusted data.
               During page generation, the application does not prevent the data from containing content that is executable by a web browser, such as JavaScript, HTML tags, HTML attributes, mouse events, Flash, ActiveX, etc.
               A victim visits the generated web page through a web browser, which contains malicious script that was injected using the untrusted data.
               Since the script comes from a web page that was sent by the web server, the victim's web browser executes the malicious script in the context of the web server's domain.
               This effectively violates the intention of the web browser's same-origin policy, which states that scripts in one domain should not be able to access resources or run code in a different domain.
            
            There are three main kinds of XSS:
            
               
                  Type 1: Reflected XSS (or Non-Persistent) - 
         			The server reads data directly from the HTTP request and reflects it back in the HTTP response. Reflected XSS exploits occur when an attacker causes a victim to supply dangerous content to a vulnerable web application, which is then reflected back to the victim and executed by the web browser. The most common mechanism for delivering malicious content is to include it as a parameter in a URL that is posted publicly or e-mailed directly to the victim. URLs constructed in this manner constitute the core of many phishing schemes, whereby an attacker convinces a victim to visit a URL that refers to a vulnerable site. After the site reflects the attacker's content back to the victim, the content is executed by the victim's browser.
               
                  Type 2: Stored XSS (or Persistent) - 
               The application stores dangerous data in a database, message forum, visitor log, or other trusted data store. At a later time, the dangerous data is subsequently read back into the application and included in dynamic content. From an attacker's perspective, the optimal place to inject malicious content is in an area that is displayed to either many users or particularly interesting users. Interesting users typically have elevated privileges in the application or interact with sensitive data that is valuable to the attacker. If one of these users executes malicious content, the attacker may be able to perform privileged operations on behalf of the user or gain access to sensitive data belonging to the user. For example, the attacker might inject XSS into a log message, which might not be handled properly when an administrator views the logs.
            
               
                  Type 0: DOM-Based XSS - 
               In DOM-based XSS, the client performs the injection of XSS into the page; in the other types, the server performs the injection. DOM-based XSS generally involves server-controlled, trusted script that is sent to the client, such as Javascript that performs sanity checks on a form before the user submits it. If the server-supplied script processes user-supplied data and then injects it back into the web page (such as with dynamic HTML), then DOM-based XSS is possible.
            
            
            Once the malicious script is injected, the attacker can perform a variety of malicious activities. The attacker could transfer private information, such as cookies that may include session information, from the victim's machine to the attacker. The attacker could send malicious requests to a web site on behalf of the victim, which could be especially dangerous to the site if the victim has administrator privileges to manage that site. Phishing attacks could be used to emulate trusted web sites and trick the victim into entering a password, allowing the attacker to compromise the victim's account on that web site. Finally, the script could exploit a vulnerability in the web browser itself possibly taking over the victim's machine, sometimes referred to as "drive-by hacking."
            In many cases, the attack can be launched without the victim even being aware of it. Even with careful users, attackers frequently use a variety of methods to encode the malicious portion of the attack, such as URL encoding or Unicode, so the request looks less suspicious.
         
         

Fix information:
repo_url: https://github.com/btcpayserver/btcpayserver
commit_details: repo_url: https://github.com/btcpayserver/btcpayserver
author: Nicolas Dorier
author_date: 2021-09-09 21:51:28+09:00
msg: Add CSP at the website level (#2863)
repository: repo_url: https://github.com/btcpayserver/btcpayserver
repo_name: btcpayserver/btcpayserver
description: Accept Bitcoin payments. Free, open-source & self-hosted, Bitcoin payment processor. 
repo_language: C#
owner: btcpayserver
file_changes: filename: BTCPayServerTester.cs
change_type: ModificationType.MODIFY
diff: @@ -134,7 +134,7 @@ namespace BTCPayServer.Tests
             config.AppendLine($"torrcfile={TestUtils.GetTestDataFullPath("Tor/torrc")}");
             config.AppendLine($"socksendpoint={SocksEndpoint}");
             config.AppendLine($"debuglog=debug.log");
-
+            config.AppendLine($"nocsp={NoCSP.ToString().ToLowerInvariant()}");
 
             if (!string.IsNullOrEmpty(SSHPassword) && string.IsNullOrEmpty(SSHKeyFile))
                 config.AppendLine($"sshpassword={SSHPassword}");
@@ -283,6 +283,8 @@ namespace BTCPayServer.Tests
         public string SSHPassword { get; internal set; }
         public string SSHKeyFile { get; internal set; }
         public string SSHConnection { get; set; }
+        public bool NoCSP { get; set; }
+
         public T GetController<T>(string userId = null, string storeId = null, bool isAdmin = false) where T : Controller
         {
             var context = new DefaultHttpContext();

programming_language: C#
filename: SeleniumTester.cs
change_type: ModificationType.MODIFY
diff: @@ -38,6 +38,7 @@ namespace BTCPayServer.Tests
 
         public async Task StartAsync()
         {
+            Server.PayTester.NoCSP = true;
             await Server.StartAsync();
 
             var windowSize = (Width: 1200, Height: 1000);

programming_language: C#
filename: Default.cshtml
change_type: ModificationType.MODIFY
diff: @@ -67,7 +67,7 @@ else
 @if (!disabled)
 {
 
-    <script type="text/javascript">
+    <script type="text/javascript" csp-sha256>
 
     var supportsWebSockets = 'WebSocket' in window && window.WebSocket.CLOSING === 2;
 

programming_language: HTML
filename: DefaultConfiguration.cs
change_type: ModificationType.MODIFY
diff: @@ -28,6 +28,7 @@ namespace BTCPayServer.Configuration
             app.Option("--chains | -c", $"Chains to support as a comma separated (default: btc; available: {chains})", CommandOptionType.SingleValue);
             app.Option("--postgres", $"Connection string to a PostgreSQL database", CommandOptionType.SingleValue);
             app.Option("--mysql", $"Connection string to a MySQL database", CommandOptionType.SingleValue);
+            app.Option("--nocsp", $"Disable CSP (default false)", CommandOptionType.BoolValue);
             app.Option("--sqlitefile", $"File name to an SQLite database file inside the data directory", CommandOptionType.SingleValue);
             app.Option("--externalservices", $"Links added to external services inside Server Settings / Services under the format service1:path2;service2:path2.(default: empty)", CommandOptionType.SingleValue);
             app.Option("--bundlejscss", $"Bundle JavaScript and CSS files for better performance (default: true)", CommandOptionType.SingleValue);

programming_language: C#
filename: ContentSecurityPolicyAttribute.cs
change_type: ModificationType.MODIFY
diff: @@ -7,13 +7,32 @@ using Microsoft.AspNetCore.Mvc.Filters;
 namespace BTCPayServer.Filters
 {
     public interface IContentSecurityPolicy : IFilterMetadata { }
+    public enum CSPTemplate
+    {
+        AntiXSS
+    }
     public class ContentSecurityPolicyAttribute : Attribute, IActionFilter, IContentSecurityPolicy
     {
-        public void OnActionExecuted(ActionExecutedContext context)
+        public ContentSecurityPolicyAttribute()
         {
 
         }
+        public ContentSecurityPolicyAttribute(CSPTemplate template)
+        {
+            if (template == CSPTemplate.AntiXSS)
+            {
+                AutoSelf = false;
+                FixWebsocket = false;
+                UnsafeInline = false;
+                ScriptSrc = "'self' 'unsafe-eval'"; // unsafe-eval needed for vue
+            }
+        }
+
+        public void OnActionExecuted(ActionExecutedContext context)
+        {
 
+        }
+        public bool Enabled { get; set; } = true;
         public bool AutoSelf { get; set; } = true;
         public bool UnsafeInline { get; set; } = true;
         public bool FixWebsocket { get; set; } = true;
@@ -22,83 +41,79 @@ namespace BTCPayServer.Filters
         public string DefaultSrc { get; set; }
         public string StyleSrc { get; set; }
         public string ScriptSrc { get; set; }
+        public string ManifestSrc { get; set; }
 
         public void OnActionExecuting(ActionExecutingContext context)
         {
-            if (context.IsEffectivePolicy<IContentSecurityPolicy>(this))
+            if (!context.IsEffectivePolicy<IContentSecurityPolicy>(this) || !Enabled)
+                return;
+            var policies = context.HttpContext.RequestServices.GetService(typeof(ContentSecurityPolicies)) as ContentSecurityPolicies;
+            if (policies == null)
+                return;
+            if (DefaultSrc != null)
             {
-                var policies = context.HttpContext.RequestServices.GetService(typeof(ContentSecurityPolicies)) as ContentSecurityPolicies;
-                if (policies == null)
-                    return;
-                if (DefaultSrc != null)
-                {
-                    policies.Add(new ConsentSecurityPolicy("default-src", DefaultSrc));
-                }
-                if (UnsafeInline)
-                {
-                    policies.Add(new ConsentSecurityPolicy("script-src", "'unsafe-inline'"));
-                }
-                if (!string.IsNullOrEmpty(FontSrc))
-                {
-                    policies.Add(new ConsentSecurityPolicy("font-src", FontSrc));
-                }
+                policies.Add(new ConsentSecurityPolicy("default-src", DefaultSrc));
+            }
+            if (UnsafeInline)
+            {
+                policies.Add(new ConsentSecurityPolicy("script-src", "'unsafe-inline'"));
+            }
+            if (!string.IsNullOrEmpty(FontSrc))
+            {
+                policies.Add(new ConsentSecurityPolicy("font-src", FontSrc));
+            }
+            if (!string.IsNullOrEmpty(ManifestSrc))
+            {
+                policies.Add(new ConsentSecurityPolicy("manifest-src", FontSrc));
+            }
 
-                if (!string.IsNullOrEmpty(ImgSrc))
-                {
-                    policies.Add(new ConsentSecurityPolicy("img-src", ImgSrc));
-                }
+            if (!string.IsNullOrEmpty(ImgSrc))
+            {
+                policies.Add(new ConsentSecurityPolicy("img-src", ImgSrc));
+            }
 
-                if (!string.IsNullOrEmpty(StyleSrc))
-                {
-                    policies.Add(new ConsentSecurityPolicy("style-src", StyleSrc));
-                }
+            if (!string.IsNullOrEmpty(StyleSrc))
+            {
+                policies.Add(new ConsentSecurityPolicy("style-src", StyleSrc));
+            }
 
-                if (!string.IsNullOrEmpty(ScriptSrc))
-                {
-                    policies.Add(new ConsentSecurityPolicy("script-src", ScriptSrc));
-                }
+            if (!string.IsNullOrEmpty(ScriptSrc))
+            {
+                policies.Add(new ConsentSecurityPolicy("script-src", ScriptSrc));
+            }
 
-                if (FixWebsocket && AutoSelf) // Self does not match wss:// and ws:// :(
-                {
-                    var request = context.HttpContext.Request;
+            if (FixWebsocket && AutoSelf) // Self does not match wss:// and ws:// :(
+            {
+                var request = context.HttpContext.Request;
 
-                    var url = string.Concat(
-                            request.Scheme.Equals("http", StringComparison.OrdinalIgnoreCase) ? "ws" : "wss",
-                            "://",
-                            request.Host.ToUriComponent(),
-                            request.PathBase.ToUriComponent());
-                    policies.Add(new ConsentSecurityPolicy("connect-src", url));
-                }
+                var url = string.Concat(
+                        request.Scheme.Equals("http", StringComparison.OrdinalIgnoreCase) ? "ws" : "wss",
+                        "://",
+                        request.Host.ToUriComponent(),
+                        request.PathBase.ToUriComponent());
+                policies.Add(new ConsentSecurityPolicy("connect-src", url));
+            }
 
-                context.HttpContext.Response.OnStarting(() =>
+            context.HttpContext.Response.OnStarting(() =>
+            {
+                if (!policies.HasRules)
+                    return Task.CompletedTask;
+                if (AutoSelf)
                 {
-                    if (!policies.HasRules)
-                        return Task.CompletedTask;
-                    if (AutoSelf)
+                    bool hasSelf = false;
+                    foreach (var group in policies.Rules.GroupBy(p => p.Name))
                     {
-                        bool hasSelf = false;
-                        foreach (var group in policies.Rules.GroupBy(p => p.Name))
+                        hasSelf = group.Any(g => g.Value.Contains("'self'", StringComparison.OrdinalIgnoreCase));
+                        if (!hasSelf && !group.Any(g => g.Value.Contains("'none'", StringComparison.OrdinalIgnoreCase) ||
+                                           g.Value.Contains("*", StringComparison.OrdinalIgnoreCase)))
                         {
-                            hasSelf = group.Any(g => g.Value.Contains("'self'", StringComparison.OrdinalIgnoreCase));
-                            if (!hasSelf && !group.Any(g => g.Value.Contains("'none'", StringComparison.OrdinalIgnoreCase) ||
-                                               g.Value.Contains("*", StringComparison.OrdinalIgnoreCase)))
-                            {
-                                policies.Add(new ConsentSecurityPolicy(group.Key, "'self'"));
-                                hasSelf = true;
-                            }
-                            if (hasSelf)
-                            {
-                                foreach (var authorized in policies.Authorized)
-                                {
-                                    policies.Add(new ConsentSecurityPolicy(group.Key, authorized));
-                                }
-                            }
+                            policies.Add(new ConsentSecurityPolicy(group.Key, "'self'"));
                         }
                     }
-                    context.HttpContext.Response.SetHeader("Content-Security-Policy", policies.ToString());
-                    return Task.CompletedTask;
-                });
-            }
+                }
+                context.HttpContext.Response.SetHeader("Content-Security-Policy", policies.ToString());
+                return Task.CompletedTask;
+            });
         }
     }
 }

programming_language: C#
filename: Startup.cs
change_type: ModificationType.MODIFY
diff: @@ -114,14 +114,8 @@ namespace BTCPayServer.Hosting
                 o.Filters.Add(new XXSSProtectionAttribute());
                 o.Filters.Add(new ReferrerPolicyAttribute("same-origin"));
                 o.ModelBinderProviders.Insert(0, new ModelBinders.DefaultModelBinderProvider());
-                //o.Filters.Add(new ContentSecurityPolicyAttribute()
-                //{
-                //    FontSrc = "'self' https://fonts.gstatic.com/",
-                //    ImgSrc = "'self' data:",
-                //    DefaultSrc = "'none'",
-                //    StyleSrc = "'self' 'unsafe-inline'",
-                //    ScriptSrc = "'self' 'unsafe-inline'"
-                //});
+                if (!Configuration.GetOrDefault<bool>("nocsp", false))
+                    o.Filters.Add(new ContentSecurityPolicyAttribute(CSPTemplate.AntiXSS));
         })
             .ConfigureApiBehaviorOptions(options =>
             {

programming_language: C#
filename: ContentSecurityPolicies.cs
change_type: ModificationType.MODIFY
diff: @@ -9,6 +9,8 @@ namespace BTCPayServer.Security
     {
         public ConsentSecurityPolicy(string name, string value)
         {
+            if (value.Contains(';', StringComparison.OrdinalIgnoreCase))
+                throw new FormatException();
             _Value = value;
             _Name = name;
         }
@@ -67,6 +69,10 @@ namespace BTCPayServer.Security
         }
 
         readonly HashSet<ConsentSecurityPolicy> _Policies = new HashSet<ConsentSecurityPolicy>();
+        public void Add(string name, string value)
+        {
+            Add(new ConsentSecurityPolicy(name, value));
+        }
         public void Add(ConsentSecurityPolicy policy)
         {
             if (_Policies.Any(p => p.Name == policy.Name && p.Value == policy.Name))
@@ -87,16 +93,12 @@ namespace BTCPayServer.Security
                 {
                     value.Append(';');
                 }
-                List<string> values = new List<string>();
+                HashSet<string> values = new HashSet<string>();
                 values.Add(group.Key);
                 foreach (var v in group)
                 {
                     values.Add(v.Value);
                 }
-                foreach (var i in authorized)
-                {
-                    values.Add(i);
-                }
                 value.Append(String.Join(" ", values.OfType<object>().ToArray()));
                 firstGroup = false;
             }
@@ -105,16 +107,7 @@ namespace BTCPayServer.Security
 
         internal void Clear()
         {
-            authorized.Clear();
             _Policies.Clear();
         }
-
-        readonly HashSet<string> authorized = new HashSet<string>();
-        internal void AddAllAuthorized(string v)
-        {
-            authorized.Add(v);
-        }
-
-        public IEnumerable<string> Authorized => authorized;
     }
 }

programming_language: C#
filename: TagHelpers.cs
change_type: ModificationType.ADD
diff: @@ -0,0 +1,128 @@
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using BTCPayServer.Security;
+using BTCPayServer.Services;
+using Microsoft.AspNetCore.Razor.TagHelpers;
+using NBitcoin;
+using NBitcoin.Crypto;
+
+namespace BTCPayServer.TagHelpers
+{
+    [HtmlTargetElement("srv-model")]
+    public class SrvModel : TagHelper
+    {
+        private readonly Safe _safe;
+        private readonly ContentSecurityPolicies _csp;
+
+        public SrvModel(Safe safe, ContentSecurityPolicies csp)
+        {
+            _safe = safe;
+            _csp = csp;
+        }
+        public string VarName { get; set; } = "srvModel";
+        public object Model { get; set; }
+        public override void Process(TagHelperContext context, TagHelperOutput output)
+        {
+            output.TagName = "script";
+            output.TagMode = TagMode.StartTagAndEndTag;
+            output.Attributes.Add(new TagHelperAttribute("type", "text/javascript"));
+            var nonce = RandomUtils.GetUInt256().ToString().Substring(0, 32);
+            output.Attributes.Add(new TagHelperAttribute("nonce", nonce));
+            _csp.Add("script-src", $"'nonce-{nonce}'");
+            output.Content.SetHtmlContent($"var {VarName} = {_safe.Json(Model)};");
+        }
+    }
+
+    /// <summary>
+    /// Add a nonce-* so the inline-script can pass CSP rule when they are rendered server-side
+    /// </summary>
+    [HtmlTargetElement("script")]
+    public class CSPInlineScriptTagHelper : TagHelper
+    {
+        private readonly ContentSecurityPolicies _csp;
+
+        public CSPInlineScriptTagHelper(ContentSecurityPolicies csp)
+        {
+            _csp = csp;
+        }
+
+        public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
+        {
+            if (output.Attributes.ContainsName("src"))
+                return;
+            if (output.Attributes.TryGetAttribute("type", out var attr))
+            {
+                if (attr.Value?.ToString() != "text/javascript")
+                    return;
+            }
+            if (output.Attributes.ContainsName("csp-sha256"))
+            {
+                var sha = CSPEventTagHelper.GetSha256((await output.GetChildContentAsync(true)).GetContent());
+                _csp.Add("script-src", $"'sha256-{sha}'");
+                output.Attributes.RemoveAll("csp-sha256");
+            }
+            else
+            {
+                var nonce = RandomUtils.GetUInt256().ToString().Substring(0, 32);
+                output.Attributes.Add(new TagHelperAttribute("nonce", nonce));
+                _csp.Add("script-src", $"'nonce-{nonce}'");
+            }
+        }
+    }
+
+    /// <summary>
+    /// Add 'unsafe-hashes' and sha256- to allow inline event handlers in CSP
+    /// </summary>
+    [HtmlTargetElement(Attributes = "onclick")]
+    [HtmlTargetElement(Attributes = "onkeypress")]
+    [HtmlTargetElement(Attributes = "onchange")]
+    [HtmlTargetElement(Attributes = "onsubmit")]
+    [HtmlTargetElement(Attributes = "href")]
+    public class CSPEventTagHelper : TagHelper
+    {
+        public const string EventNames = "onclick,onkeypress,onchange,onsubmit";
+        private readonly ContentSecurityPolicies _csp;
+
+        readonly static HashSet<string> EventSet = EventNames.Split(',')
+                                                    .ToHashSet();
+        public CSPEventTagHelper(ContentSecurityPolicies csp)
+        {
+            _csp = csp;
+        }
+        public override void Process(TagHelperContext context, TagHelperOutput output)
+        {
+            foreach (var attr in output.Attributes)
+            {
+                var n = attr.Name.ToLowerInvariant();
+                if (EventSet.Contains(n))
+                {
+                    Allow(attr.Value.ToString());
+                }
+                else if (n == "href")
+                {
+                    var v = attr.Value.ToString();
+                    if (v.StartsWith("javascript:", StringComparison.OrdinalIgnoreCase))
+                    {
+                        Allow(v);
+                    }
+                }
+            }
+        }
+
+        private void Allow(string v)
+        {
+            var sha = GetSha256(v);
+            _csp.Add("script-src", $"'unsafe-hashes'");
+            _csp.Add("script-src", $"'sha256-{sha}'");
+        }
+
+        public static string GetSha256(string script)
+        {
+            return Convert.ToBase64String(Hashes.SHA256(Encoding.UTF8.GetBytes(script.Replace("\r\n", "\n", StringComparison.Ordinal))));
+        }
+    }
+}

programming_language: C#
filename: PosData.cshtml
change_type: ModificationType.MODIFY
diff: @@ -1,7 +1,7 @@
 @model (Dictionary<string, object> Items, int Level)
 
 @functions{
-    void DisplayValue(object value)
+    async Task DisplayValue(object value)
     {
         if (value is string str && str.StartsWith("http"))
         {
@@ -25,7 +25,7 @@
                     <th class="w-150px">@key</th>
                 }
                 <td>
-                    @{ DisplayValue(value); }
+                    @{ await DisplayValue(value); }
                 </td>
             }
             else if (value is Dictionary<string, object>subItems)
@@ -35,7 +35,7 @@
                 {
                     <th class="w-150px">@key</th>
                     <td>
-                        @{ DisplayValue(subItems.First().Value); }
+                        @{ await DisplayValue(subItems.First().Value); }
                     </td>
                 }
                 else

programming_language: C#