diff --git a/api/src/org/labkey/api/assay/actions/AssayRunUploadForm.java b/api/src/org/labkey/api/assay/actions/AssayRunUploadForm.java
index 583dc3de7d0..dfab0aa4eda 100644
--- a/api/src/org/labkey/api/assay/actions/AssayRunUploadForm.java
+++ b/api/src/org/labkey/api/assay/actions/AssayRunUploadForm.java
@@ -59,6 +59,7 @@
 import org.labkey.api.study.StudyService;
 import org.labkey.api.study.publish.StudyPublishService;
 import org.labkey.api.study.assay.ParticipantVisitResolverType;
+import org.labkey.api.util.FileUtil;
 import org.labkey.api.util.GUID;
 import org.labkey.api.view.ActionURL;
 import org.labkey.api.view.NotFoundException;
@@ -360,7 +361,7 @@ public Map<DomainProperty, FileLike> getAdditionalPostedFiles(List<? extends Dom
                             String previousFileName = request.getParameter(fileParam);
                             if (null != previousFileName)
                             {
-                                previousFile = new File(getAssayDirectory(getContainer(), null).getAbsolutePath(), previousFileName);
+                                previousFile = FileUtil.appendName(getAssayDirectory(getContainer(), null), previousFileName);
 
                                 MultipartFile multiFile = ((MultipartHttpServletRequest)request).getFileMap().get(UploadWizardAction.getInputName(fileParameters.get(fileParam)));
 
diff --git a/api/src/org/labkey/api/attachments/FileAttachmentFile.java b/api/src/org/labkey/api/attachments/FileAttachmentFile.java
index 3e8eec51918..7021d847e96 100644
--- a/api/src/org/labkey/api/attachments/FileAttachmentFile.java
+++ b/api/src/org/labkey/api/attachments/FileAttachmentFile.java
@@ -17,6 +17,7 @@
 package org.labkey.api.attachments;
 
 import org.apache.logging.log4j.Logger;
+import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 import org.labkey.api.util.PageFlowUtil;
 import org.labkey.api.util.logging.LogHelper;
@@ -40,22 +41,22 @@ public class FileAttachmentFile implements AttachmentFile
 
     private InputStream _in;
 
-    public FileAttachmentFile(File file)
+    public FileAttachmentFile(@NotNull File file)
     {
         this(file, null);
     }
 
-    public FileAttachmentFile(FileLike file)
+    public FileAttachmentFile(@NotNull FileLike file)
     {
         this(file.toNioPathForRead().toFile(), null);
     }
 
-    public FileAttachmentFile(FileLike file, @Nullable String originalName)
+    public FileAttachmentFile(@NotNull FileLike file, @Nullable String originalName)
     {
         this(file.toNioPathForRead().toFile(), originalName);
     }
 
-    public FileAttachmentFile(File file, @Nullable String originalName)
+    public FileAttachmentFile(@NotNull File file, @Nullable String originalName)
     {
         _file = file;
         _filename = null != originalName ? originalName : file.getName();
diff --git a/api/src/org/labkey/api/exp/AbstractFileXarSource.java b/api/src/org/labkey/api/exp/AbstractFileXarSource.java
index 273e1ef3202..1b57d449e29 100644
--- a/api/src/org/labkey/api/exp/AbstractFileXarSource.java
+++ b/api/src/org/labkey/api/exp/AbstractFileXarSource.java
@@ -20,7 +20,9 @@
 import org.fhcrc.cpas.exp.xml.ExperimentArchiveDocument;
 import org.jetbrains.annotations.Nullable;
 import org.labkey.api.data.Container;
+import org.labkey.api.pipeline.PipeRoot;
 import org.labkey.api.pipeline.PipelineJob;
+import org.labkey.api.pipeline.PipelineService;
 import org.labkey.api.security.User;
 import org.labkey.api.util.FileUtil;
 import org.labkey.api.util.NetworkDrive;
@@ -30,6 +32,7 @@
 import java.io.InputStream;
 import java.net.URI;
 import java.nio.file.Files;
+import java.nio.file.InvalidPathException;
 import java.nio.file.Path;
 import java.util.Map;
 
@@ -113,6 +116,14 @@ public String canonicalizeDataFileURL(String dataFileURL)
         if (!uri.isAbsolute())
         {
             Path path = xarDirectory.resolve(dataFileURL);
+            if (!path.normalize().startsWith(xarDirectory.normalize()))
+            {
+                // check alternative - relative to container pipeline root
+                PipeRoot root = PipelineService.get().findPipelineRoot(getXarContext().getContainer());
+                boolean valid = root != null && root.isUnderRoot(path);
+                if (!valid)
+                    throw new InvalidPathException(dataFileURL, "Path to parent not allowed");
+            }
             String result = _dataFileURLs.get(FileUtil.getAbsolutePath(getXarContext().getContainer(), path));
             if (result != null)
             {
diff --git a/api/src/org/labkey/api/files/FileContentService.java b/api/src/org/labkey/api/files/FileContentService.java
index c78a0d74c59..9791ba68902 100644
--- a/api/src/org/labkey/api/files/FileContentService.java
+++ b/api/src/org/labkey/api/files/FileContentService.java
@@ -218,7 +218,7 @@ enum ContentType {
      * relative to the first parent container with an override
      */
     File getDefaultRoot(Container c, boolean createDir);
-    Path getDefaultRootPath(Container c, boolean createDir);
+    Path getDefaultRootPath(@NotNull Container c, boolean createDir);
 
     class DefaultRootInfo
     {
diff --git a/api/src/org/labkey/api/pipeline/AnalyzeForm.java b/api/src/org/labkey/api/pipeline/AnalyzeForm.java
index bf09d3072a7..9a69e371a9c 100644
--- a/api/src/org/labkey/api/pipeline/AnalyzeForm.java
+++ b/api/src/org/labkey/api/pipeline/AnalyzeForm.java
@@ -20,6 +20,7 @@
 import org.labkey.api.pipeline.file.AbstractFileAnalysisProtocol;
 import org.labkey.api.security.User;
 import org.labkey.api.util.FileType;
+import org.labkey.api.util.FileUtil;
 
 import java.nio.file.Path;
 
@@ -96,7 +97,7 @@ private String initStatusFile(AbstractFileAnalysisProtocol protocol, Path dirDat
         }
         else if (fileInputName != null)
         {
-            Path fileInput = dirData.resolve(fileInputName);
+            Path fileInput = FileUtil.appendName(dirData, fileInputName);
             FileType ft = protocol.findInputType(fileInput);
             if (ft != null)
                 fileStatus = PipelineJob.FT_LOG.newFile(dirAnalysis, ft.getBaseName(fileInput));
diff --git a/api/src/org/labkey/api/pipeline/LocalDirectory.java b/api/src/org/labkey/api/pipeline/LocalDirectory.java
index 0a05628ea58..c614f3f5470 100644
--- a/api/src/org/labkey/api/pipeline/LocalDirectory.java
+++ b/api/src/org/labkey/api/pipeline/LocalDirectory.java
@@ -137,7 +137,7 @@ public Path determineLogFile()
         {
             try
             {
-                Path remoteLogFilePath = _remoteDir.resolve(_logFile.getFileName().toString());
+                Path remoteLogFilePath = FileUtil.appendName(_remoteDir, _logFile.getFileName().toString());
                 if (Files.exists(remoteLogFilePath))
                 {
                     Files.copy(remoteLogFilePath, _logFile);
@@ -307,6 +307,6 @@ public Path getRemoteLogFilePath()
     {
         if (_remoteDir == null)
             return _logFile;
-        return _remoteDir.resolve(_logFile.getFileName().toString());
+        return FileUtil.appendName(_remoteDir, _logFile.getFileName().toString());
     }
 }
diff --git a/api/src/org/labkey/api/query/AbstractQueryImportAction.java b/api/src/org/labkey/api/query/AbstractQueryImportAction.java
index 60ad82ff709..960ce45f70d 100644
--- a/api/src/org/labkey/api/query/AbstractQueryImportAction.java
+++ b/api/src/org/labkey/api/query/AbstractQueryImportAction.java
@@ -472,26 +472,6 @@ else if (StringUtils.isNotBlank(path))
                     file = resource.getFileStream(user);
                     originalName = resource.getName();
                 }
-                else
-                {
-                    // Resolve file under pipeline root
-                    PipeRoot root = PipelineService.get().findPipelineRoot(getContainer());
-                    if (root != null)
-                    {
-                        // Attempt absolute path first, then relative path from pipeline root
-                        File f = new File(path);
-                        if (!root.isUnderRoot(f))
-                            f = root.resolvePath(path);
-
-                        if (NetworkDrive.exists(f) && root.isUnderRoot(f) && root.hasPermission(getContainer(), getUser(), ReadPermission.class))
-                        {
-                            hasPostData = true;
-                            loader = DataLoader.get().createLoader(f, null, _hasColumnHeaders, null, null);
-                            file = new FileAttachmentFile(dataFile, f.getName());
-                            originalName = f.getName();
-                        }
-                    }
-                }
 
                 if (!hasPostData)
                 {
diff --git a/api/src/org/labkey/api/util/FileType.java b/api/src/org/labkey/api/util/FileType.java
index 245be11eb19..0e36e910abe 100644
--- a/api/src/org/labkey/api/util/FileType.java
+++ b/api/src/org/labkey/api/util/FileType.java
@@ -244,7 +244,7 @@ private String tryName(Path parentDir, String name)
     {
         if (_supportGZ.booleanValue())  // TPP treats xml.gz as a native format
         {   // in the case of existing files, non-gz copy wins if present
-            Path f = parentDir!=null ? parentDir.resolve(name) : Path.of(name);
+            Path f = parentDir!=null ? FileUtil.appendName(parentDir, name) : Path.of(name);
             if (!NetworkDrive.exists(f))
             {  // non-gz copy doesn't exist - how about .gz version?
                 String gzname = name + ".gz";
@@ -252,7 +252,7 @@ private String tryName(Path parentDir, String name)
                 {   // we like .gz for new filenames, so don't care if exists
                     return gzname;
                 }
-                f = parentDir!=null ? parentDir.resolve(gzname) : Path.of(gzname);
+                f = parentDir!=null ? FileUtil.appendName(parentDir, gzname) : Path.of(gzname);
                 if (NetworkDrive.exists(f))
                 { // we don't prefer .gz, but we support it if it exists
                     return gzname;
@@ -464,7 +464,7 @@ else if (_supportGZ.booleanValue()) // TPP treats .xml.gz as a native read forma
 
     public File newFile(File parent, String basename)
     {
-        return new File(parent, getName(parent, basename));
+        return FileUtil.appendName(parent, getName(parent, basename));
     }
 
     public Path newFile(Path parent, String basename)
diff --git a/experiment/src/org/labkey/experiment/controllers/exp/ExperimentController.java b/experiment/src/org/labkey/experiment/controllers/exp/ExperimentController.java
index 5045e2fb26a..657d28931d0 100644
--- a/experiment/src/org/labkey/experiment/controllers/exp/ExperimentController.java
+++ b/experiment/src/org/labkey/experiment/controllers/exp/ExperimentController.java
@@ -6758,7 +6758,7 @@ public Object execute(Object o, BindException errors) throws Exception
             {
                 userDirName = GUEST_DIRECTORY_NAME;
             }
-            Path userDir = uploadDir.resolve(userDirName);
+            Path userDir = FileUtil.appendName(uploadDir, userDirName);
             FileUtil.createDirectories(userDir);
             if (!Files.isDirectory(userDir))
             {
@@ -6766,7 +6766,7 @@ public Object execute(Object o, BindException errors) throws Exception
                 return false;
             }
 
-            Path xarFile = userDir.resolve(formFile.getOriginalFilename());
+            Path xarFile = FileUtil.appendName(userDir, formFile.getOriginalFilename());
 
             // As this is multi-part will need to use finally to close, to prevent a stream closure exception
             try (OutputStream out = new BufferedOutputStream(Files.newOutputStream(xarFile)))
diff --git a/experiment/src/org/labkey/experiment/pipeline/ExperimentPipelineProvider.java b/experiment/src/org/labkey/experiment/pipeline/ExperimentPipelineProvider.java
index cdf33f5429b..4d797234e81 100644
--- a/experiment/src/org/labkey/experiment/pipeline/ExperimentPipelineProvider.java
+++ b/experiment/src/org/labkey/experiment/pipeline/ExperimentPipelineProvider.java
@@ -73,12 +73,12 @@ public void initSystemDirectory(Path rootDir, Path systemDir)
 
     public void locateSystemDir(Path systemDir, String name)
     {
-        Path path = systemDir.resolve(name);
+        Path path = FileUtil.appendName(systemDir, name);
         if (Files.exists(path))
         {
             try
             {
-                Path dest = getExperimentDirectory(systemDir, name).resolve(FileUtil.getFileName(path));
+                Path dest = FileUtil.appendName(getExperimentDirectory(systemDir, name), FileUtil.getFileName(path));
                 Files.move(path, dest);
             }
             catch (IOException e)
diff --git a/filecontent/src/org/labkey/filecontent/FileContentServiceImpl.java b/filecontent/src/org/labkey/filecontent/FileContentServiceImpl.java
index 436f9ff9940..da9fe34706a 100644
--- a/filecontent/src/org/labkey/filecontent/FileContentServiceImpl.java
+++ b/filecontent/src/org/labkey/filecontent/FileContentServiceImpl.java
@@ -310,7 +310,7 @@ public File getDefaultRoot(Container c, boolean createDir)
     }
 
     @Override
-    public java.nio.file.Path getDefaultRootPath(Container c, boolean createDir)
+    public java.nio.file.Path getDefaultRootPath(@NotNull Container c, boolean createDir)
     {
         Container firstOverride = getFirstAncestorWithOverride(c);
 
@@ -325,7 +325,7 @@ public java.nio.file.Path getDefaultRootPath(Container c, boolean createDir)
             parentRoot = getFileRootPath(firstOverride);
         }
 
-        if (parentRoot != null && c != null && firstOverride != null)
+        if (parentRoot != null && firstOverride != null)
         {
             java.nio.file.Path fileRootPath;
             if (FileUtil.hasCloudScheme(parentRoot))
@@ -336,7 +336,7 @@ public java.nio.file.Path getDefaultRootPath(Container c, boolean createDir)
             else
             {
                 // For local, the path may be several directories deep (since it matches the LK folder path), so we should create the directories for that path
-                fileRootPath = new File(parentRoot.toFile(), getRelativePath(c, firstOverride)).toPath();
+                fileRootPath = FileUtil.appendPath(parentRoot.toFile(), Path.parse(getRelativePath(c, firstOverride))).toPath();
 
                 try
                 {
@@ -395,7 +395,7 @@ public FileRoot getDefaultFileRoot(Container c)
         return null;
     }
 
-    private String getRelativePath(Container c, Container ancestor)
+    private @NotNull String getRelativePath(Container c, Container ancestor)
     {
         return c.getPath().replaceAll("^" + Pattern.quote(ancestor.getPath()), "");
     }
diff --git a/filecontent/src/org/labkey/filecontent/FileSystemAttachmentParent.java b/filecontent/src/org/labkey/filecontent/FileSystemAttachmentParent.java
index f126ae7a031..e425e51da14 100644
--- a/filecontent/src/org/labkey/filecontent/FileSystemAttachmentParent.java
+++ b/filecontent/src/org/labkey/filecontent/FileSystemAttachmentParent.java
@@ -126,7 +126,7 @@ else if (isRelative())
 
             if (_contentType != null && !svc.isCloudRoot(container))    // don't need @files in cloud
             {
-                Path root = dir.resolve(svc.getFolderName(_contentType));
+                Path root = FileUtil.appendName(dir, svc.getFolderName(_contentType));
 
                 // Issue 49963: avoid FileAlreadyExistsExceptions on certain file systems
                 if (!Files.exists(root) && Files.isWritable(dir) && create)
diff --git a/pipeline/src/org/labkey/pipeline/api/PipelineServiceImpl.java b/pipeline/src/org/labkey/pipeline/api/PipelineServiceImpl.java
index aad92c76ece..3f2e1db3837 100644
--- a/pipeline/src/org/labkey/pipeline/api/PipelineServiceImpl.java
+++ b/pipeline/src/org/labkey/pipeline/api/PipelineServiceImpl.java
@@ -986,7 +986,7 @@ public String startFileAnalysis(AnalyzeForm form, @Nullable Map<String, String>
             {
                 try
                 {
-                    Files.move(inputFile, dirData.resolve(inputFile.getFileName().toString()));
+                    Files.move(inputFile, FileUtil.appendName(dirData, inputFile.getFileName().toString()));
                 }
                 catch (IOException e)
                 {
diff --git a/study/src/org/labkey/study/assay/StudyPublishManager.java b/study/src/org/labkey/study/assay/StudyPublishManager.java
index 35888fa0a36..d4a2cc2c894 100644
--- a/study/src/org/labkey/study/assay/StudyPublishManager.java
+++ b/study/src/org/labkey/study/assay/StudyPublishManager.java
@@ -958,7 +958,7 @@ public UploadLog saveUploadData(User user, Dataset dsd, FileStream tsv, String f
             String extra = id++ == 0 ? "" : String.valueOf(id);
             String fileName = dsd.getStudy().getLabel() + "-" + dsd.getLabel() + "-" + dateString + extra + "." + extension;
             fileName = fileName.replace('\\', '_').replace('/', '_').replace(':', '_');
-            file = dir.resolve(fileName);
+            file = FileUtil.appendName(dir, fileName);
         }
         while (Files.exists(file));
 
diff --git a/study/src/org/labkey/study/importer/StudyImportContext.java b/study/src/org/labkey/study/importer/StudyImportContext.java
index 2d81c65b41e..1adf4a587f5 100644
--- a/study/src/org/labkey/study/importer/StudyImportContext.java
+++ b/study/src/org/labkey/study/importer/StudyImportContext.java
@@ -131,7 +131,7 @@ private Path getStudyFile(VirtualFile root, VirtualFile dir, String name) throws
     {
         Path rootFile = FileUtil.stringToPath(getContainer(), root.getLocation());
         Path dirFile = FileUtil.stringToPath(getContainer(), dir.getLocation());
-        Path file = dirFile.resolve(name);
+        Path file = FileUtil.appendName(dirFile, name);
         String source = "study.xml";
 
         if (!Files.exists(file))