peass-ng/PEASS-ng · error · ArgumentException

Resources.Not_A_Valid_Guid

Error message

Resources.Not_A_Valid_Guid

What it means

AlphaFS Volume.SetVolumeMountPoint validates that the volumeGuid argument looks like a volume GUID path before calling the Win32 SetVolumeMountPoint API. When the string does not start with the \\?\Volume{ prefix (the form \\?\Volume{GUID}\), it throws ArgumentException with the Resources.Not_A_Valid_Guid message naming volumeGuid. This fail-fast check avoids passing a malformed path to the native API.

Source

Thrown at winPEAS/winPEASexe/winPEAS/3rdParty/AlphaFS/Device/Volume/Volume.SetVolumeMountPoint.cs:51

      /// <exception cref="ArgumentException"/>
      /// <exception cref="ArgumentNullException"/>
      /// <param name="volumeMountPoint">
      ///   The user-mode path to be associated with the volume. This may be a Drive letter (for example, "X:\")
      ///   or a directory on another volume (for example, "Y:\MountX\").
      /// </param>
      /// <param name="volumeGuid">A <see cref="string"/> containing the volume <see cref="Guid"/>.</param>      
      [SuppressMessage("Microsoft.Design", "CA1062:Validate arguments of public methods", MessageId = "1", Justification = "Utils.IsNullOrWhiteSpace validates arguments.")]
      [SecurityCritical]
      public static void SetVolumeMountPoint(string volumeMountPoint, string volumeGuid)
      {
         if (Utils.IsNullOrWhiteSpace(volumeMountPoint))
            throw new ArgumentNullException("volumeMountPoint");

         if (Utils.IsNullOrWhiteSpace(volumeGuid))
            throw new ArgumentNullException("volumeGuid");

         if (!volumeGuid.StartsWith(Path.VolumePrefix + "{", StringComparison.OrdinalIgnoreCase))
            throw new ArgumentException(Resources.Not_A_Valid_Guid, "volumeGuid");


         volumeMountPoint = Path.GetFullPathCore(null, false, volumeMountPoint, GetFullPathOptions.AsLongPath | GetFullPathOptions.AddTrailingDirectorySeparator | GetFullPathOptions.FullCheck);


         // This string must be of the form "\\?\Volume{GUID}\"
         volumeGuid = Path.AddTrailingDirectorySeparator(volumeGuid, false);


         // ChangeErrorMode is for the Win32 SetThreadErrorMode() method, used to suppress possible pop-ups.
         using (new NativeMethods.ChangeErrorMode(NativeMethods.ErrorMode.FailCriticalErrors))
         {
            // SetVolumeMountPoint()
            // 2014-01-29: MSDN does not confirm LongPath usage but a Unicode version of this function exists.

            // The string must end with a trailing backslash.
            var success = NativeMethods.SetVolumeMountPoint(volumeMountPoint, volumeGuid);

View on GitHub (pinned to 53fb989abc)

Solutions

1. Obtain the GUID string via Volume.GetVolumeNameForVolumeMountPoint / Volume.EnumerateVolumes (FindFirstVolume), which returns the full \\?\Volume{GUID}\ form, and pass that value.
2. If you only have the raw GUID, prepend the prefix and append a trailing separator yourself, e.g. "\\?\Volume{" + guid.Trim('{','}') + "}\".
3. Verify argument order: the first parameter is volumeMountPoint (the NTFS folder to mount at), the second is volumeGuid; swapping them causes this error.
4. Pass a non-empty, non-whitespace string; null/empty raises ArgumentNullException before this check.

Example fix

// before
string guid = "{4a1f2b3c-...}"; // from registry
Volume.SetVolumeMountPoint("C:\\Mount", guid);
// after
string guid = Volume.GetVolumeNameForVolumeMountPoint("C:\"); // "\\?\Volume{4a1f2b3c-...}\"
Volume.SetVolumeMountPoint("C:\\Mount", guid);

static bool IsVolumeGuidPath(string s) =>
    !string.IsNullOrWhiteSpace(s) &&
    s.StartsWith("\\\\?\\Volume{", StringComparison.OrdinalIgnoreCase) &&
    s.EndsWith("}\\");

bool IsValidVolumeGuid(string s) =>
    s != null && s.Contains("Volume{") && Guid.TryParse(s.Trim('\\', '{', '}'), out _);

try { Volume.SetVolumeMountPoint(mountPoint, volumeGuid); }
catch (ArgumentException ex) when (ex.ParamName == "volumeGuid")
{
    // malformed GUID; regenerate via Volume.GetVolumeNameForVolumeMountPoint
}

When it happens

Trigger: Calling Volume.SetVolumeMountPoint with a volumeGuid that is a bare GUID string like '{GUID}' or 'X\', a drive letter, a path without the \\?\Volume{ prefix, or a null/empty string that somehow passed the earlier null check.

Common situations: Developers store volume GUIDs from registry or WMI output (which often lack the \\?\Volume{...}\ wrapper) and pass them directly; mixing up a mount point path and the volume GUID argument; older AlphaFS versions or code copied from snippets using QueryDosDevice output instead of FindFirstVolume/GetVolumeNameForVolumeMountPoint results.

Related errors

• Resources.InvalidDriveLetterArgument
• rootPathName
• volumeName
• volumeName
• Value cannot be null. Parameter name: path

AI-assisted analysis of peass-ng/PEASS-ng@53fb989abc (2026-09-02). Data as JSON: /api/errors/73a32ba29db684f0. Report an issue: GitHub.