From 1c39c8d5efca4ffa3fa2994a520dd461c4fd42c1 Mon Sep 17 00:00:00 2001
From: James Crosswell <jamescrosswell@users.noreply.github.com>
Date: Wed, 25 Jun 2025 10:23:23 +1200
Subject: [PATCH 1/3] Treat empty trace id as invalid when parsing trace
 headers

---
 .../Extensions/HttpContextExtensions.cs           |  9 ++++++++-
 .../Extensions/HttpContextExtensionsTests.cs      | 15 +++++++++++++++
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/src/Sentry.AspNetCore/Extensions/HttpContextExtensions.cs b/src/Sentry.AspNetCore/Extensions/HttpContextExtensions.cs
index 19e4dde3c4..9eb982036a 100644
--- a/src/Sentry.AspNetCore/Extensions/HttpContextExtensions.cs
+++ b/src/Sentry.AspNetCore/Extensions/HttpContextExtensions.cs
@@ -56,7 +56,14 @@ internal static class HttpContextExtensions
 
         try
         {
-            return SentryTraceHeader.Parse(value!);
+            var traceHeader = SentryTraceHeader.Parse(value!);
+            if (traceHeader?.TraceId != SentryId.Empty)
+            {
+                return traceHeader;
+            }
+
+            options?.LogWarning("Sentry trace header '{0}' has an empty trace ID.", value);
+            return null;
         }
         catch (Exception ex)
         {
diff --git a/test/Sentry.AspNetCore.Tests/Extensions/HttpContextExtensionsTests.cs b/test/Sentry.AspNetCore.Tests/Extensions/HttpContextExtensionsTests.cs
index c116976049..339d661a4b 100644
--- a/test/Sentry.AspNetCore.Tests/Extensions/HttpContextExtensionsTests.cs
+++ b/test/Sentry.AspNetCore.Tests/Extensions/HttpContextExtensionsTests.cs
@@ -78,5 +78,20 @@ public void TryGetRouteTemplate_WithSentryRouteName_RouteName()
         // Assert
         Assert.Equal(expectedName, filteredRoute);
     }
+
+    [Fact]
+    public void TryGetSentryTraceHeader_WithEmptyTraceId_ReturnsNull()
+    {
+        // Arrange
+        var httpContext = Fixture.GetSut();
+        var options = new SentryOptions();
+        httpContext.Request.Headers.Append(SentryTraceHeader.HttpHeaderName, "00000000000000000000000000000000-1000000000000000-1");
+
+        // Act
+        var header = httpContext.TryGetSentryTraceHeader(options);
+
+        // Assert
+        Assert.Null(header);
+    }
 }
 #endif

From 457f70d6200b71c375cbb00845cde55c9118ad4e Mon Sep 17 00:00:00 2001
From: James Crosswell <jamescrosswell@users.noreply.github.com>
Date: Wed, 25 Jun 2025 10:58:18 +1200
Subject: [PATCH 2/3] Fixed NoOpSpan.GetTraceHeader()

---
 src/Sentry/Internal/UnsampledSpan.cs          |  1 +
 .../Internals/UnsampledSpanTests.cs           | 24 +++++++++++++++++++
 2 files changed, 25 insertions(+)
 create mode 100644 test/Sentry.Tests/Internals/UnsampledSpanTests.cs

diff --git a/src/Sentry/Internal/UnsampledSpan.cs b/src/Sentry/Internal/UnsampledSpan.cs
index 3b52bdaa8c..ae64942ef0 100644
--- a/src/Sentry/Internal/UnsampledSpan.cs
+++ b/src/Sentry/Internal/UnsampledSpan.cs
@@ -6,4 +6,5 @@ internal sealed class UnsampledSpan(UnsampledTransaction transaction, SpanId? sp
     public override SpanId SpanId { get; } = spanId ?? SpanId.Empty;
     internal UnsampledTransaction Transaction => transaction;
     public override ISpan StartChild(string operation) => transaction.StartChild(operation);
+    public override SentryTraceHeader GetTraceHeader() => transaction.GetTraceHeader();
 }
diff --git a/test/Sentry.Tests/Internals/UnsampledSpanTests.cs b/test/Sentry.Tests/Internals/UnsampledSpanTests.cs
new file mode 100644
index 0000000000..a64edc9eed
--- /dev/null
+++ b/test/Sentry.Tests/Internals/UnsampledSpanTests.cs
@@ -0,0 +1,24 @@
+namespace Sentry.Tests.Internals;
+
+public class UnsampledSpanTests
+{
+    [Fact]
+    public void GetTraceHeader_CreatesHeaderFromUnsampledTransaction()
+    {
+        // Arrange
+        var hub = Substitute.For<IHub>();
+        ITransactionContext context = new TransactionContext("TestTransaction", "TestOperation",
+            new SentryTraceHeader(SentryId.Create(), SpanId.Create(), false)
+        );
+        var transaction = new UnsampledTransaction(hub, context);
+        var unsampledSpan = transaction.StartChild("Foo");
+
+        // Act
+        var traceHeader = unsampledSpan.GetTraceHeader();
+
+        // Assert
+        traceHeader.TraceId.Should().Be(context.TraceId);
+        traceHeader.SpanId.Should().Be(context.SpanId);
+        traceHeader.IsSampled.Should().Be(context.IsSampled);
+    }
+}

From 69fd3a047b1816a8a89dfbcb4bd3a020cff0db4a Mon Sep 17 00:00:00 2001
From: James Crosswell <jamescrosswell@users.noreply.github.com>
Date: Wed, 25 Jun 2025 11:04:37 +1200
Subject: [PATCH 3/3] Update CHANGELOG.md

---
 CHANGELOG.md | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 054dfd7fe2..002c64191c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,11 @@
 # Changelog
 
+## Unreleased
+
+### Fixes
+
+- Unsampled spans no longer propagate empty trace headers ([#4302](https://github.com/getsentry/sentry-dotnet/pull/4302))
+
 ## 5.11.1
 
 ### Fixes