Prevent SSRF, local file disclosure and DoS via external references in SVG rendering

2 files changed, 119 insertions, 0 deletions

diff --git a/tests/Jellyfin.Drawing.Skia.Tests/Jellyfin.Drawing.Skia.Tests.csproj b/tests/Jellyfin.Drawing.Skia.Tests/Jellyfin.Drawing.Skia.Tests.csproj
new file mode 100644
index 0000000000..b6dc5dfb92
--- /dev/null
+++ b/tests/Jellyfin.Drawing.Skia.Tests/Jellyfin.Drawing.Skia.Tests.csproj
@@ -0,0 +1,26 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <!-- ProjectGuid is only included as a requirement for SonarQube analysis -->
+  <PropertyGroup>
+    <ProjectGuid>{E24A279C-9A37-419A-8F9C-853C11FBE753}</ProjectGuid>
+    <OutputType>Exe</OutputType>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.NET.Test.Sdk" />
+    <PackageReference Include="xunit.v3" />
+    <PackageReference Include="xunit.runner.visualstudio">
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      <PrivateAssets>all</PrivateAssets>
+    </PackageReference>
+    <PackageReference Include="coverlet.collector">
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      <PrivateAssets>all</PrivateAssets>
+    </PackageReference>
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="../../src/Jellyfin.Drawing.Skia/Jellyfin.Drawing.Skia.csproj" />
+  </ItemGroup>
+
+</Project>
diff --git a/tests/Jellyfin.Drawing.Skia.Tests/SvgSecurityValidatorTests.cs b/tests/Jellyfin.Drawing.Skia.Tests/SvgSecurityValidatorTests.cs
new file mode 100644
index 0000000000..62f35694f1
--- /dev/null
+++ b/tests/Jellyfin.Drawing.Skia.Tests/SvgSecurityValidatorTests.cs
@@ -0,0 +1,93 @@
+using System.IO;
+using Microsoft.Extensions.Logging.Abstractions;
+using Xunit;
+
+namespace Jellyfin.Drawing.Skia.Tests;
+
+public static class SvgSecurityValidatorTests
+{
+    public static TheoryData<string> ExternalReferenceSvgs => new()
+    {
+        // SSRF via <image> (xlink:href and plain href)
+        "<svg xmlns='http://www.w3.org/2000/svg' xmlns:xlink='http://www.w3.org/1999/xlink' width='16' height='16'><image xlink:href='http://169.254.169.254/latest/meta-data/' width='16' height='16'/></svg>",
+        "<svg xmlns='http://www.w3.org/2000/svg' width='16' height='16'><image href='https://example.invalid/a.png' width='16' height='16'/></svg>",
+        // Local file disclosure
+        "<svg xmlns='http://www.w3.org/2000/svg' xmlns:xlink='http://www.w3.org/1999/xlink' width='16' height='16'><image xlink:href='file:///etc/passwd' width='16' height='16'/></svg>",
+        // Memory exhaustion DoS
+        "<svg xmlns='http://www.w3.org/2000/svg' xmlns:xlink='http://www.w3.org/1999/xlink' width='16' height='16'><image xlink:href='file:///dev/urandom' width='16' height='16'/></svg>",
+        // <use> external reference
+        "<svg xmlns='http://www.w3.org/2000/svg' xmlns:xlink='http://www.w3.org/1999/xlink' width='16' height='16'><use xlink:href='http://example.invalid/c.svg#a'/></svg>",
+        // CSS url() external reference in an attribute
+        "<svg xmlns='http://www.w3.org/2000/svg' width='16' height='16'><rect width='16' height='16' style=\"fill:url(http://example.invalid/d.svg#g)\"/></svg>",
+        // @import in a style block
+        "<svg xmlns='http://www.w3.org/2000/svg' width='16' height='16'><style>@import 'http://example.invalid/e.css';</style><rect width='16' height='16'/></svg>",
+        // Relative path traversal (resolves against the document location -> local file read)
+        "<svg xmlns='http://www.w3.org/2000/svg' xmlns:xlink='http://www.w3.org/1999/xlink' width='16' height='16'><image xlink:href='../../../../etc/hosts' width='16' height='16'/></svg>",
+        // XXE via external entity
+        "<?xml version='1.0'?><!DOCTYPE svg [<!ENTITY xxe SYSTEM 'file:///etc/passwd'>]><svg xmlns='http://www.w3.org/2000/svg' width='16' height='16'><text>&xxe;</text></svg>",
+        // Entity-expansion (billion laughs) denial of service
+        "<?xml version='1.0'?><!DOCTYPE svg [<!ENTITY a 'aaaaaaaaaa'><!ENTITY b '&a;&a;&a;&a;&a;&a;&a;&a;&a;&a;'><!ENTITY c '&b;&b;&b;&b;&b;&b;&b;&b;&b;&b;'><!ENTITY d '&c;&c;&c;&c;&c;&c;&c;&c;&c;&c;'><!ENTITY e '&d;&d;&d;&d;&d;&d;&d;&d;&d;&d;'><!ENTITY f '&e;&e;&e;&e;&e;&e;&e;&e;&e;&e;'>]><svg xmlns='http://www.w3.org/2000/svg' width='16' height='16'><text>&f;</text></svg>",
+        // Nested SVG in a base64 data: URI whose inner document references an external resource
+        "<svg xmlns='http://www.w3.org/2000/svg' xmlns:xlink='http://www.w3.org/1999/xlink' width='16' height='16'><image xlink:href='data:image/svg+xml;base64,PHN2ZyB4bWxucz0naHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmcnIHhtbG5zOnhsaW5rPSdodHRwOi8vd3d3LnczLm9yZy8xOTk5L3hsaW5rJyB3aWR0aD0nOCcgaGVpZ2h0PSc4Jz48aW1hZ2UgeGxpbms6aHJlZj0naHR0cDovL2V4YW1wbGUuaW52YWxpZC9uZXN0ZWQucG5nJyB3aWR0aD0nOCcgaGVpZ2h0PSc4Jy8+PC9zdmc+' width='16' height='16'/></svg>",
+        // Nested SVG in a URL-encoded (non-base64) data: URI referencing an external resource
+        "<svg xmlns='http://www.w3.org/2000/svg' xmlns:xlink='http://www.w3.org/1999/xlink' width='16' height='16'><image xlink:href='data:image/svg+xml,%3Csvg%20xmlns%3D%27http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%27%20xmlns%3Axlink%3D%27http%3A%2F%2Fwww.w3.org%2F1999%2Fxlink%27%3E%3Cimage%20xlink%3Ahref%3D%27file%3A%2F%2F%2Fetc%2Fpasswd%27%2F%3E%3C%2Fsvg%3E' width='16' height='16'/></svg>",
+    };
+
+    public static TheoryData<string> SafeSvgs => new()
+    {
+        "<svg xmlns='http://www.w3.org/2000/svg' width='16' height='16'><rect width='16' height='16' fill='red'/></svg>",
+        // Same-document fragment references are allowed
+        "<svg xmlns='http://www.w3.org/2000/svg' xmlns:xlink='http://www.w3.org/1999/xlink' width='16' height='16'><defs><linearGradient id='g'/></defs><rect width='16' height='16' fill='url(#g)'/><use xlink:href='#g'/></svg>",
+        // Inline data URIs are allowed
+        "<svg xmlns='http://www.w3.org/2000/svg' xmlns:xlink='http://www.w3.org/1999/xlink' width='16' height='16'><image xlink:href='data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVR42mP8z8BQDwAEhQGAhKmMIQAAAABJRU5ErkJggg==' width='16' height='16'/></svg>",
+        // A DOCTYPE without external entities is allowed
+        "<?xml version='1.0'?><!DOCTYPE svg PUBLIC '-//W3C//DTD SVG 1.1//EN' 'http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd'><svg xmlns='http://www.w3.org/2000/svg' width='16' height='16'><rect width='16' height='16'/></svg>",
+        // An internal general entity with no external reference is allowed (and is expanded by the renderer)
+        "<?xml version='1.0'?><!DOCTYPE svg [<!ENTITY col 'red'>]><svg xmlns='http://www.w3.org/2000/svg' width='16' height='16'><rect width='16' height='16' fill='&col;'/></svg>",
+        // A nested data:image/svg+xml payload that is itself self-contained is allowed
+        "<svg xmlns='http://www.w3.org/2000/svg' xmlns:xlink='http://www.w3.org/1999/xlink' width='16' height='16'><image xlink:href='data:image/svg+xml;base64,PHN2ZyB4bWxucz0naHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmcnIHdpZHRoPSc4JyBoZWlnaHQ9JzgnPjxyZWN0IHdpZHRoPSc4JyBoZWlnaHQ9JzgnIGZpbGw9J2JsdWUnLz48L3N2Zz4=' width='16' height='16'/></svg>",
+    };
+
+    [Theory]
+    [MemberData(nameof(ExternalReferenceSvgs))]
+    public static void IsSafe_ExternalReference_ReturnsFalse(string svg)
+    {
+        var path = WriteTemp(svg);
+        try
+        {
+            Assert.False(SvgSecurityValidator.IsSafe(path, NullLogger.Instance));
+        }
+        finally
+        {
+            File.Delete(path);
+        }
+    }
+
+    [Theory]
+    [MemberData(nameof(SafeSvgs))]
+    public static void IsSafe_NoExternalReference_ReturnsTrue(string svg)
+    {
+        var path = WriteTemp(svg);
+        try
+        {
+            Assert.True(SvgSecurityValidator.IsSafe(path, NullLogger.Instance));
+        }
+        finally
+        {
+            File.Delete(path);
+        }
+    }
+
+    [Fact]
+    public static void IsSafe_MissingFile_ReturnsFalse()
+    {
+        Assert.False(SvgSecurityValidator.IsSafe(Path.Combine(Path.GetTempPath(), "does-not-exist-" + Path.GetRandomFileName() + ".svg"), NullLogger.Instance));
+    }
+
+    private static string WriteTemp(string svg)
+    {
+        var path = Path.Combine(Path.GetTempPath(), Path.GetRandomFileName() + ".svg");
+        File.WriteAllText(path, svg);
+        return path;
+    }
+}