Insecure Permission Assignment for Garmin OAuth Token Store

Summary

garminconnect (≤ 0.3.4) wrote its OAuth token store to disk without restricting file-system permissions. Under the default Linux umask (022) the token file garmin_tokens.json was created world-readable (0o644). The file contains the DI refresh token, so any other local user on a shared host could read it and obtain persistent, unauthorized access to the victim's Garmin Connect account.

• Severity: High
• Weakness: CWE-732 (Incorrect Permission Assignment for Critical Resource)
• Affected versions: <= 0.3.4
• Patched version: 0.3.5

Details

Client.dump() created the token directory and file with no mode argument, leaving permissions entirely to the process umask:

def dump(self, path: str) -> None:
    p = Path(path).expanduser()
    if p.is_dir() or not p.name.endswith(".json"):
        p = p / "garmin_tokens.json"
    p.parent.mkdir(parents=True, exist_ok=True)   # no mode=
    p.write_text(self.dumps())                     # no permission restriction

The serialized payload includes di_token, di_refresh_token, and di_client_id. The call is in the core library (Garmin.login(tokenstore=...) persists tokens this way), and all shipped usage examples default the token store to ~/.garminconnect.

Under umask 022 the resulting permissions were:

• token directory → 0o755
• garmin_tokens.json → 0o644 (world-readable)

A separate, unprivileged user on the same machine could read the file with a plain open() — no elevated privileges required — and extract the refresh token.

Impact

Local credential theft / privilege escalation on multi-user Linux or macOS hosts running under a permissive umask. The stolen refresh token can be exchanged for fresh access tokens via Garmin's OAuth endpoint, granting ongoing access to the victim's account (health/fitness data, activity history, device management) until the token is revoked.

Patch

Fixed in 0.3.5 (commit 77a3837). dump() now creates the directory as 0o700 and writes the token file as 0o600 regardless of umask — using os.open(..., O_CREAT|O_WRONLY|O_TRUNC, 0o600) with O_NOFOLLOW where available, plus a defensive chmod that also tightens a pre-existing loose file:

p.parent.mkdir(mode=0o700, parents=True, exist_ok=True)
with contextlib.suppress(OSError):
    p.parent.chmod(0o700)
flags = os.O_WRONLY | os.O_CREAT | os.O_TRUNC
if hasattr(os, "O_NOFOLLOW"):
    flags |= os.O_NOFOLLOW
fd = os.open(p, flags, 0o600)
with os.fdopen(fd, "w", encoding="utf-8") as f:
    f.write(self.dumps())
with contextlib.suppress(OSError):
    p.chmod(0o600)

Verified under umask 022: directory 0o700, file 0o600, no group/other access.

Workarounds

If you cannot upgrade immediately, restrict the token store manually and keep it owner-only:

chmod 700 ~/.garminconnect
chmod 600 ~/.garminconnect/garmin_tokens.json

Remediation

1. Upgrade to garminconnect >= 0.3.5:

   pip install --upgrade garminconnect

2. Fix any token file already on disk — upgrading only tightens permissions
   on the next write, so an existing world-readable file stays exposed until
   then:

   chmod 600 ~/.garminconnect/garmin_tokens.json
   # or remove it and log in again to mint a fresh token store

3. If the file was exposed on a shared host, treat the refresh token as
   compromised. Re-authenticate (delete the token store and log in again) so
   a new token is issued; consider the previously stored token potentially
   read by others until rotated.

Credit

Reported by EQSTLab via a private security advisory. garminconnect thanks them for the detailed, responsible disclosure.

References

• GHSA-wjhr-76vg-2hvc
• cyberjunky/python-garminconnect@77a3837
• cyberjunky/python-garminconnect@f74174a
• https://github.com/cyberjunky/python-garminconnect/releases/tag/0.3.5