diff --git a/dotnet/Directory.Packages.props b/dotnet/Directory.Packages.props
index f4a51a045a48..534116db67a1 100644
--- a/dotnet/Directory.Packages.props
+++ b/dotnet/Directory.Packages.props
@@ -13,7 +13,7 @@
     <PackageVersion Include="CommunityToolkit.Aspire.Hosting.Dapr" Version="9.9.0" />
     <PackageVersion Include="CommunityToolkit.Aspire.Hosting.NodeJS.Extensions" Version="9.9.0" />
     <PackageVersion Include="Aspire.Hosting.Azure.Search" Version="13.4.6" />
-    <PackageVersion Include="MessagePack" Version="3.1.7" /> <!-- Transitive dependency of Aspire pinned to newer version due to vulnerability in 2.5.192 -->
+    <PackageVersion Include="MessagePack" Version="3.1.9" /> <!-- Transitive dependency of Aspire pinned to newer version due to vulnerability in 2.5.192 -->
     <PackageVersion Include="AWSSDK.BedrockAgent" Version="4.0.100.8" />
     <PackageVersion Include="AWSSDK.BedrockAgentRuntime" Version="4.0.100.7" />
     <PackageVersion Include="AWSSDK.BedrockRuntime" Version="4.0.101.1" />
diff --git a/dotnet/src/Plugins/Plugins.Core/CodeInterpreter/SessionsPythonPlugin.cs b/dotnet/src/Plugins/Plugins.Core/CodeInterpreter/SessionsPythonPlugin.cs
index 9433de2a86bb..681298cd0dc7 100644
--- a/dotnet/src/Plugins/Plugins.Core/CodeInterpreter/SessionsPythonPlugin.cs
+++ b/dotnet/src/Plugins/Plugins.Core/CodeInterpreter/SessionsPythonPlugin.cs
@@ -111,7 +111,7 @@ public async Task<SessionsPythonCodeExecutionResult> ExecuteCodeAsync(
     /// <summary>
     /// Uploads a file to the `/mnt/data` directory of the current session.
     /// </summary>
-    /// <param name="remoteFileName">The name of the remote file, relative to `/mnt/data`.</param>
+    /// <param name="remoteFileName">The name of the remote file, relative to `/mnt/data`. Must not be rooted or contain `.` or `..` path segments.</param>
     /// <param name="localFilePath">The path to the file on the local machine.</param>
     /// <param name="cancellationToken">The cancellation token.</param>
     /// <returns>The metadata of the uploaded file.</returns>
@@ -120,13 +120,14 @@ public async Task<SessionsPythonCodeExecutionResult> ExecuteCodeAsync(
     /// <exception cref="InvalidOperationException">Thrown when file operations are disabled or the path is not allowed.</exception>
     [KernelFunction, Description("Uploads a file to the `/mnt/data` directory of the current session.")]
     public async Task<SessionsRemoteFileMetadata> UploadFileAsync(
-        [Description("The name of the remote file, relative to `/mnt/data`.")] string remoteFileName,
+        [Description("The name of the remote file, relative to `/mnt/data`. Must not be rooted or contain `.` or `..` path segments.")] string remoteFileName,
         [Description("The path to the file on the local machine.")] string localFilePath,
         CancellationToken cancellationToken = default)
     {
         Verify.NotNullOrWhiteSpace(remoteFileName, nameof(remoteFileName));
         Verify.NotNullOrWhiteSpace(localFilePath, nameof(localFilePath));
 
+        ValidateRemoteFileName(remoteFileName);
         var validatedLocalPath = this.ValidateLocalPathForUpload(localFilePath);
 
         this._logger.LogInformation("Uploading file: {LocalFilePath} to {RemoteFileName}", validatedLocalPath, remoteFileName);
@@ -292,6 +293,21 @@ private async Task<HttpResponseMessage> SendAsync(HttpClient httpClient, HttpMet
         return await httpClient.SendWithSuccessCheckAsync(request, cancellationToken).ConfigureAwait(false);
     }
 
+    private static void ValidateRemoteFileName(string remoteFileName)
+    {
+        var hasDrivePrefix = remoteFileName.Length >= 2
+            && remoteFileName[1] == ':'
+            && char.IsLetter(remoteFileName[0]);
+
+        if (remoteFileName[0] is '/' or '\\'
+            || hasDrivePrefix
+            || remoteFileName.Split('/', '\\').Any(segment => segment is "." or ".."))
+        {
+            throw new InvalidOperationException(
+                "The remote file name must be relative and must not contain '.' or '..' path segments.");
+        }
+    }
+
     /// <summary>
     /// Validates that the local file path is within allowed upload directories.
     /// </summary>
diff --git a/dotnet/src/Plugins/Plugins.UnitTests/Core/SessionsPythonPluginTests.cs b/dotnet/src/Plugins/Plugins.UnitTests/Core/SessionsPythonPluginTests.cs
index 7899f6fb9c2d..ce262555f183 100644
--- a/dotnet/src/Plugins/Plugins.UnitTests/Core/SessionsPythonPluginTests.cs
+++ b/dotnet/src/Plugins/Plugins.UnitTests/Core/SessionsPythonPluginTests.cs
@@ -278,6 +278,61 @@ public async Task ItShouldUploadFileAsync()
         Assert.Equal(this._messageHandlerStub.FirstMultipartContent, requestPayload);
     }
 
+    [Theory]
+    [InlineData(".")]
+    [InlineData("..")]
+    [InlineData("../test-file.txt")]
+    [InlineData("../../test-file.txt")]
+    [InlineData("./test-file.txt")]
+    [InlineData("nested/./test-file.txt")]
+    [InlineData("nested/../test-file.txt")]
+    [InlineData("nested/..")]
+    [InlineData("/mnt/data/../../test-file.txt")]
+    [InlineData(@"nested\.\test-file.txt")]
+    [InlineData(@"nested\..\test-file.txt")]
+    [InlineData(@"\test-file.txt")]
+    [InlineData(@"\\server\share\test-file.txt")]
+    [InlineData(@"C:\test-file.txt")]
+    [InlineData("C:test-file.txt")]
+    [InlineData("C:/test-file.txt")]
+    [InlineData("/test-file.txt")]
+    public async Task ItShouldRejectUnsafeUploadRemoteFileNamesAsync(string remoteFileName)
+    {
+        // Arrange
+        var plugin = new SessionsPythonPlugin(this._settingsWithFileOperationsEnabled, this._httpClientFactory);
+
+        // Act
+        var exception = await Assert.ThrowsAsync<InvalidOperationException>(
+            () => plugin.UploadFileAsync(remoteFileName, FileTestDataFilePath));
+
+        // Assert
+        Assert.Contains("must not contain '.' or '..' path segments", exception.Message);
+        Assert.Null(this._messageHandlerStub.RequestUri);
+    }
+
+    [Theory]
+    [InlineData("nested/dir/test-file.txt")]
+    [InlineData(@"nested\dir\test-file.txt")]
+    [InlineData(".hidden/test-file.txt")]
+    [InlineData("nested/a..b/test-file.txt")]
+    public async Task ItShouldAllowSafeUploadRemoteFileNamesAsync(string remoteFileName)
+    {
+        // Arrange
+        var responseContent = await File.ReadAllTextAsync(UpdaloadFileTestDataFilePath);
+        this._messageHandlerStub.ResponseToReturn = new HttpResponseMessage(HttpStatusCode.OK)
+        {
+            Content = new StringContent(responseContent),
+        };
+
+        var plugin = new SessionsPythonPlugin(this._settingsWithFileOperationsEnabled, this._httpClientFactory);
+
+        // Act
+        await plugin.UploadFileAsync(remoteFileName, FileTestDataFilePath);
+
+        // Assert
+        Assert.NotNull(this._messageHandlerStub.RequestUri);
+    }
+
     [Fact]
     public async Task ItShouldDownloadFileWithoutSavingInDiskAsync()
     {