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Resolve favicon extraction target DNS host once per connection (#2310)

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This commit is contained in:
Leendert de Borst
2026-08-02 19:23:16 +02:00
committed by Leendert de Borst
parent ce331df98a
commit 90ea7d6bb4
3 changed files with 93 additions and 41 deletions
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15
apps/server/Tests/AliasVault.UnitTests/Utilities/FaviconExtractorTests.cs
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@@ -7,6 +7,8 @@
namespace AliasVault.UnitTests.Utilities;
using System.Net;
/// <summary>
/// Tests for the AliasVault.FaviconExtractor class.
/// </summary>
@@ -91,4 +93,17 @@ public class FaviconExtractorTests
Assert.That(faviconBytes, Is.Null, $"Should block non-standard port URL: {url}");
}
}
/// <summary>
/// Check that a mixed set of public and private IP addresses is rejected as only fully public sets are allowed.
/// </summary>
[Test]
public void RejectsAddressSetMixingPublicAndPrivate()
{
Assert.Multiple(() =>
{
Assert.That(FaviconExtractor.FaviconExtractor.AreIpAddressesPublic([IPAddress.Parse("8.8.8.8"), IPAddress.Parse("10.0.0.1")]), Is.False, "A mixed set must be rejected");
Assert.That(FaviconExtractor.FaviconExtractor.AreIpAddressesPublic([IPAddress.Parse("8.8.8.8"), IPAddress.Parse("1.1.1.1")]), Is.True, "An all-public set must be allowed");
});
}
}

4
apps/server/Utilities/AliasVault.FaviconExtractor/AliasVault.FaviconExtractor.csproj
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@@ -17,6 +17,10 @@
<DocumentationFile>bin\Release\net10.0\FaviconExtractor.xml</DocumentationFile>
</PropertyGroup>
<ItemGroup>
<InternalsVisibleTo Include="AliasVault.UnitTests" />
</ItemGroup>
<ItemGroup>
<AdditionalFiles Include="..\..\stylecop.json" Link="stylecop.json" />
</ItemGroup>

115
apps/server/Utilities/AliasVault.FaviconExtractor/FaviconExtractor.cs
View File

@@ -9,10 +9,13 @@ namespace AliasVault.FaviconExtractor;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Net.Sockets;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using HtmlAgilityPack;
using SkiaSharp;
@@ -88,22 +91,30 @@ public static class FaviconExtractor
url = NormalizeUrl(url);
Uri uri = new(url);
if (!IsValidUri(uri))
if (!IsAllowedSchemeAndPort(uri))
{
return null;
}
using HttpClient client = CreateHttpClient();
// Attempt the operation up to two times to handle common cookiewall redirects or transient issues.
for (int attempt = 0; attempt < 2; attempt++)
try
{
var result = await TryGetFaviconAsync(client, uri);
if (result != null)
// Attempt the operation up to two times to handle common cookiewall redirects or transient issues.
for (int attempt = 0; attempt < 2; attempt++)
{
return result;
var result = await TryGetFaviconAsync(client, uri);
if (result != null)
{
return result;
}
}
}
catch (HttpRequestException)
{
// Abort on any request exception.
return null;
}
// Return null if the favicon extraction failed.
return null;
@@ -205,6 +216,51 @@ public static class FaviconExtractor
return ImageFormatSignature.Unknown;
}
/// <summary>
/// Checks whether a set of IP addresses are all publicly routable.
/// </summary>
/// <param name="addresses">The addresses returned by one DNS resolution.</param>
/// <returns>True if all addresses are publicly routable, false otherwise.</returns>
internal static bool AreIpAddressesPublic(IPAddress[] addresses)
{
foreach (var address in addresses)
{
if (!IPAddressValidator.IsPublicIPAddress(address))
{
return false;
}
}
return true;
}
/// <summary>
/// Opens the TCP connection for an outgoing request and resolve a hostname only once.
/// </summary>
/// <param name="context">Connection context supplied by the HTTP stack.</param>
/// <param name="cancellationToken">Token to cancel the connection attempt.</param>
/// <returns>A stream over the established connection.</returns>
private static async ValueTask<Stream> ConnectToValidatedAddressAsync(SocketsHttpConnectionContext context, CancellationToken cancellationToken)
{
var addresses = await Dns.GetHostAddressesAsync(context.DnsEndPoint.Host, cancellationToken);
if (!AreIpAddressesPublic(addresses))
{
throw new HttpRequestException("Blocked connection to a non-public address.");
}
var socket = new Socket(SocketType.Stream, ProtocolType.Tcp) { NoDelay = true };
try
{
await socket.ConnectAsync(addresses, context.DnsEndPoint.Port, cancellationToken);
return new NetworkStream(socket, ownsSocket: true);
}
catch
{
socket.Dispose();
throw;
}
}
private static async Task<byte[]?> SafeGetFaviconAsync(string url)
{
try
@@ -320,7 +376,7 @@ public static class FaviconExtractor
try
{
// Validate the favicon URL before fetching
if (!Uri.TryCreate(url, UriKind.Absolute, out var faviconUri) || !IsValidUri(faviconUri))
if (!Uri.TryCreate(url, UriKind.Absolute, out var faviconUri) || !IsAllowedSchemeAndPort(faviconUri))
{
return null;
}
@@ -374,12 +430,13 @@ public static class FaviconExtractor
/// <returns>The HTTP client.</returns>
private static HttpClient CreateHttpClient()
{
var handler = new HttpClientHandler
var handler = new SocketsHttpHandler
{
AllowAutoRedirect = false, // Handle redirects manually
UseCookies = true, // Enable cookie handling for session management
CookieContainer = new System.Net.CookieContainer(),
AutomaticDecompression = System.Net.DecompressionMethods.GZip | System.Net.DecompressionMethods.Deflate | System.Net.DecompressionMethods.Brotli,
ConnectCallback = ConnectToValidatedAddressAsync,
};
var client = new HttpClient(handler)
@@ -447,37 +504,13 @@ public static class FaviconExtractor
}
/// <summary>
/// Checks if the URI is valid and not pointing to internal/private IPs.
/// Checks the URI scheme and port.
/// </summary>
/// <param name="uri">The URI to check.</param>
/// <returns>True if the URI is valid and safe, false otherwise.</returns>
private static bool IsValidUri(Uri uri)
/// <returns>True if the scheme and port are both allowed, false otherwise.</returns>
private static bool IsAllowedSchemeAndPort(Uri uri)
{
// Check scheme and port
if (!_allowedSchemes.Contains(uri.Scheme) || !uri.IsDefaultPort)
{
return false;
}
// Resolve hostname to IP and validate
try
{
var addresses = Dns.GetHostAddresses(uri.Host);
foreach (var address in addresses)
{
if (!IPAddressValidator.IsPublicIPAddress(address))
{
return false;
}
}
}
catch
{
// If DNS resolution fails, block the request
return false;
}
return true;
return _allowedSchemes.Contains(uri.Scheme) && uri.IsDefaultPort;
}
/// <summary>
@@ -498,12 +531,12 @@ public static class FaviconExtractor
var request = new HttpRequestMessage(HttpMethod.Get, currentUri);
if (redirectCount == 0)
{
// First request - add Google referer to appear like navigation
// First request: add Google referer to appear like navigation
request.Headers.Add("Referer", "https://www.google.com/");
}
else
{
// Subsequent redirects - use original URL as referer
// Subsequent redirects: use original URL as referer
request.Headers.Add("Referer", uri.ToString());
}
@@ -523,10 +556,10 @@ public static class FaviconExtractor
location = new Uri(currentUri, location);
}
// Validate the redirect target
if (!IsValidUri(location))
// Validate the target URL scheme and port.
if (!IsAllowedSchemeAndPort(location))
{
return null; // Block redirect to internal IPs
return null;
}
currentUri = location;