unslothai/unsloth · error · NativePathLeaseError

Native path grant contains invalid characters.

Error message

Native path grant contains invalid characters.

What it means

One of the grant's free-text payload fields (canonical_path, nonce, token_id_hash, display_label) contains a NUL byte (\x00). The backend refuses NUL bytes because they cannot round-trip through C-based filesystem and OS APIs and are a classic payload-injection vector. Any presence means the signed payload itself was malformed at signing time. This check runs on optional fields too (only absent fields are skipped).

Source

Thrown at studio/backend/utils/native_path_leases.py:340

    if payload["operation"] != operation:
        raise NativePathLeaseError("Native path grant operation is invalid.")
    if expected_kind and payload["path_kind"] != expected_kind:
        raise NativePathLeaseError("Native path grant kind is invalid.")
    now_ms = int(time.time() * 1000)
    issued_at_ms = _required_int(payload, "issued_at_ms")
    expires_at_ms = _required_int(payload, "expires_at_ms")
    if issued_at_ms >= expires_at_ms:
        raise NativePathLeaseError("Native path grant timestamps are inconsistent.")
    if expires_at_ms <= now_ms:
        raise NativePathLeaseError("Native path grant has expired.")
    if issued_at_ms > now_ms + 30_000:
        raise NativePathLeaseError("Native path grant issue time is invalid.")
    for key in ("canonical_path", "nonce", "token_id_hash", "display_label"):
        raw = payload.get(key)
        if raw is None:
            continue
        if "\x00" in str(raw):
            raise NativePathLeaseError("Native path grant contains invalid characters.")


def _validate_current_stat(
    grant: NativePathGrant, identity_options: tuple[tuple[int, int], ...]
) -> tuple[int, int] | None:
    try:
        st = os.lstat(grant.canonical_path)
    except OSError as exc:
        raise NativePathLeaseError("Native path is no longer accessible.") from exc
    if _stat_module.S_ISLNK(st.st_mode):
        raise NativePathLeaseError("Native path is no longer a regular file.")
    if grant.path_type == "file":
        if not _stat_module.S_ISREG(st.st_mode):
            raise NativePathLeaseError("Native path is no longer a regular file.")
    elif grant.path_type == "directory":
        if not _stat_module.S_ISDIR(st.st_mode):
            raise NativePathLeaseError("Native path is no longer a directory.")
    else:

View on GitHub (pinned to 203007d190)

Solutions

1. Decode the grant payload and locate the offending field: python -c "import base64,json;print(json.loads(base64.urlsafe_b64decode(lease.split('.')[0]+'==')))" and inspect for \x00.
2. Fix the signer to strip/reject NUL bytes before building the JSON payload.
3. Regenerate the grant; the backend cannot sanitize a signed payload (any edit breaks the HMAC).
4. Add a unit test on the signer asserting no control characters in the four string fields.

Example fix

// before (Rust signer)
let nonce = bytes_with_nul.to_vec(); // embedded \x00 leaks into JSON

// after
let nonce = String::from_utf8(bytes)?.replace('\0', "");
assert!(!nonce.contains('\0'));

import base64, json

def grant_strings_clean(lease: str) -> bool:
    payload = json.loads(base64.urlsafe_b64decode(lease.split('.')[0] + '=='))
    return all(
        '\x00' not in str(payload.get(k, ''))
        for k in ('canonical_path', 'nonce', 'token_id_hash', 'display_label')
    )

try:
    grant = verify_native_path_lease(lease, operation='read')
except NativePathLeaseError as exc:
    if 'invalid characters' in str(exc):
        lease = request_fresh_grant()  # signed payload is corrupt at source
        grant = verify_native_path_lease(lease, operation='read')
    else:
        raise

When it happens

Trigger: verify_native_path_lease() with a payload where any of canonical_path/nonce/token_id_hash/display_label contains \x00. Produced by a signer bug that embeds raw bytes instead of UTF-8 strings, or by a hand-crafted signed payload used in tests containing embedded NULs.

Common situations: Rust signer writing a fixed-size buffer or a length-prefixed value into a JSON string without trimming; test fixtures generated with struct.pack or bytes concatenation; fuzzing pipelines feeding arbitrary bytes into the grant builder.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• Native path contains invalid characters.
• Provider base URL contains invalid characters.
• A reference was sent empty.
• Native path grant timestamps are inconsistent.
• Native path grant issue time is invalid.

AI-assisted analysis of unslothai/unsloth@203007d190 (2026-08-15). Data as JSON: /api/errors/a7b16bbc7c0107e4. Report an issue: GitHub.