Review flagged this as critical and it is: the composer builds manager.py
by interpolating payload values into source text, /api/install writes
that file into plugins_dir, and the plugin loader imports and executes
it. The ast.parse check further down rejects only *invalid* syntax, and
an injected `import os` is perfectly valid.
Confirmed against the code before this commit. A plugin name carrying a
triple quote closes the module docstring and everything after it becomes
module-level code:
generated manager.py parses: True
injected module-level statements: ['import os', 'PWNED = os.getuid()']
and a geometry value is interpolated verbatim, because the parameter is
annotated int but arrives as JSON:
_compute_pos_expr('0 or __import__("os").system("id")', 'right', 'width')
-> 'width - 0 or __import__("os").system("id")'
generated source: x=0 or __import__("os").system("id"),
Three fixes. _safe_int coerces and optionally clamps, and
_compute_pos_expr applies it to its own argument -- which covers all
twenty-odd call sites at once rather than patching each. _rgb_expr does
the same for the eight colour interpolations, clamping channels to
0-255. Line endpoints and widths go through it too.
For the docstring, _reject_source_breaking refuses a plugin name
containing a quote, backslash or newline. Rejecting rather than escaping:
these are display names, none of that belongs in one, and a clear "Plugin
name cannot contain a double quote." beats silently mangling what the
user typed.
Verified: all three exploits now refused or neutered, and each defence
mutation-checked separately --
coercion removed in _compute_pos_expr -> 8 failed
docstring guard removed -> 5 failed
colour channels interpolated raw -> 13 failed
87 tests, covering seven expression payloads across seven geometry
fields and three colour channels, five literal-breaking names, and the
clean case asserting a normal payload still yields no module-level
statements at all.
One aside: the first version of this test file put the exploit string
in its own module docstring, which closed it and made the file a syntax
error -- the same bug, one level up. It now describes the payload rather
than embedding it.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01STMbQE4YctTacQXfbYqKuW
