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Merged
Shivansps merged 2 commits into from
May 9, 2026
Merged

Validate API-supplied paths to prevent directory traversal #398

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e20a3ed
Validate API-supplied paths to prevent directory traversal
Goober5000 May 6, 2026
1d8e179
fix issues
wookieejedi May 7, 2026
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47 changes: 46 additions & 1 deletion Knossos.NET/Classes/KnUtils.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -629,6 +629,28 @@ public static string CmdLineBuilder(string cmdline, string[]? args)
return cmdline;
}

/// <summary>
/// Returns true if candidatePath resolves to a location within basePath.
/// Rejects absolute paths, null bytes, and path traversal sequences such as "..".
/// </summary>
public static bool IsSubPath(string basePath, string candidatePath)
{
if (string.IsNullOrEmpty(candidatePath))
return true;
if (Path.IsPathRooted(candidatePath))
return false;
try
{
var fullBase = Path.GetFullPath(basePath).TrimEnd(Path.DirectorySeparatorChar) + Path.DirectorySeparatorChar;
var fullTarget = Path.GetFullPath(Path.Combine(basePath, candidatePath));
return fullTarget.StartsWith(fullBase, StringComparison.OrdinalIgnoreCase);
}
catch
{
return false;
}
}

/// <summary>
/// Gets the complete size of all files in a folder and subdirectories in bytes
/// </summary>
Expand Down Expand Up @@ -1009,7 +1031,24 @@ private static bool DecompressFileSharpCompress(string compressedFilePath, strin
{
if (!reader.Entry.IsDirectory)
{
reader.WriteEntryToDirectory(destFolderPath, new ExtractionOptions() { ExtractFullPath = extractFullPath, Overwrite = true, WriteSymbolicLink = (source, target) => { File.CreateSymbolicLink(source, target); } });
var entryKey = reader.Entry.Key?.Replace('\\', '/').Replace('/', Path.DirectorySeparatorChar);
if (entryKey != null && extractFullPath && !IsSubPath(destFolderPath, entryKey))
{
Log.Add(Log.LogSeverity.Warning, "KnUtils.DecompressFileSharpCompress()", $"Skipping potentially dangerous archive entry: {reader.Entry.Key}");
continue;
}
reader.WriteEntryToDirectory(destFolderPath, new ExtractionOptions() { ExtractFullPath = extractFullPath, Overwrite = true, WriteSymbolicLink = (source, target) =>
{
var resolvedTarget = Path.IsPathRooted(target)
? target
: Path.GetFullPath(Path.Combine(Path.GetDirectoryName(source)!, target));
if (!IsSubPath(destFolderPath, Path.GetRelativePath(destFolderPath, resolvedTarget)))
{
Log.Add(Log.LogSeverity.Warning, "KnUtils.DecompressFileSharpCompress()", $"Skipping symlink escaping destination: {source} -> {target}");
return;
}
File.CreateSymbolicLink(source, target);
}});
}
if (cancellationTokenSource!.IsCancellationRequested)
{
Expand All @@ -1028,6 +1067,12 @@ private static bool DecompressFileSharpCompress(string compressedFilePath, strin
{
if (!reader.Entry.IsDirectory)
{
var entryKey = reader.Entry.Key?.Replace('\\', '/').Replace('/', Path.DirectorySeparatorChar);
if (entryKey != null && extractFullPath && !IsSubPath(destFolderPath, entryKey))
{
Log.Add(Log.LogSeverity.Warning, "KnUtils.DecompressFileSharpCompress()", $"Skipping potentially dangerous archive entry: {reader.Entry.Key}");
continue;
}
reader.WriteEntryToDirectory(destFolderPath, new ExtractionOptions() { ExtractFullPath = extractFullPath, Overwrite = true });
}
if (cancellationTokenSource!.IsCancellationRequested)
Expand Down
14 changes: 12 additions & 2 deletions Knossos.NET/ViewModels/Templates/Tasks/InstallBuild.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -231,8 +231,12 @@ private async Task<bool> InstallVCRedist(bool is86 = false) {
{
if (file.dest != null && file.dest.Trim() != string.Empty)
{
var path = file.dest;
Directory.CreateDirectory(modPath + Path.DirectorySeparatorChar + path);
if (!KnUtils.IsSubPath(modPath, file.dest))
{
Log.Add(Log.LogSeverity.Error, "TaskItemViewModel.InstallBuild()", $"Unsafe dest path in build '{build.id}': {file.dest}");
CancelTaskCommand();
}
Directory.CreateDirectory(modPath + Path.DirectorySeparatorChar + file.dest);
}
}

Expand Down Expand Up @@ -277,6 +281,12 @@ private async Task<bool> InstallVCRedist(bool is86 = false) {
}

Info = "Tasks: " + ProgressCurrent + "/" + ProgressBarMax;
if (string.IsNullOrEmpty(file.filename) || !KnUtils.IsSubPath(modPath, file.filename))
{
Log.Add(Log.LogSeverity.Error, "TaskItemViewModel.InstallBuild()", $"Unsafe filename in build '{build.id}': {file.filename}");
CancelTaskCommand();
throw new TaskCanceledException();
}
var fileFullPath = modPath + Path.DirectorySeparatorChar + file.filename;
var result = await fileTask.DownloadFile(file.urls!, fileFullPath, "Downloading " + file.filename, false, null, cancellationTokenSource);

Expand Down
15 changes: 13 additions & 2 deletions Knossos.NET/ViewModels/Templates/Tasks/InstallMod.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -263,8 +263,13 @@ public async Task<bool> InstallMod(Mod mod, CancellationTokenSource cancelSource
{
if (file.dest != null && file.dest.Trim() != string.Empty)
{
var path = file.dest;
Directory.CreateDirectory(modPath + Path.DirectorySeparatorChar + path);
if (!KnUtils.IsSubPath(modPath, file.dest))
{
Log.Add(Log.LogSeverity.Error, "TaskItemViewModel.InstallMod()", $"Unsafe dest path in mod '{mod.id}': {file.dest}");
CancelTaskCommand();
return false;
}
Directory.CreateDirectory(modPath + Path.DirectorySeparatorChar + file.dest);
}
}

Expand Down Expand Up @@ -346,6 +351,12 @@ public async Task<bool> InstallMod(Mod mod, CancellationTokenSource cancelSource
{
file.dest = string.Empty;
}
if (string.IsNullOrEmpty(file.filename) || !KnUtils.IsSubPath(modPath, file.filename))
{
Log.Add(Log.LogSeverity.Error, "TaskItemViewModel.InstallMod()", $"Unsafe filename in mod '{mod.id}': {file.filename}");
CancelTaskCommand();
throw new TaskCanceledException();
}
var fileFullPath = modPath + Path.DirectorySeparatorChar + file.filename;
var result = await fileTask.DownloadFile(file.urls!, fileFullPath, "Downloading " + file.filename, false, null, cancellationTokenSource);

Expand Down