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Marius CiepluchandClaude Opus 5
d651455d23
The group-4 finding: JavaScript is callback-heavy, so the method containing a
sink routinely is not the labeled function. `fs.readFileSync` inside the
callback passed to `fs.stat` has enclosing method `<lambda>0`, and filtering on
`sinkMethod == function` dropped it -- the whole path family measured 0/8.
Scope is now decided by line-range containment within the same file
(astParentFullName is empty for lambdas, so nesting is not readable there), and
reported as `inLabeledScope`; the Python side trusts that flag and keeps the
name comparison only as a fallback, so an engine that cannot report scope never
has its sinks silently treated as scoped. Parameter sources stay bound to the
labeled function's OWN parameters -- a callback's `err`/`stats` are not
attacker input.
Fixing the scope exposed three further bugs, each of which would have raised
the number while making the answer untrue:
* Shortest-flow-wins picked the wrong witness. With closures in scope the
same sink has flows from `req.url...` (10 steps, the vulnerability), `res`
(3) and `this` (7). A flow whose source matches the source model now
outranks a shorter one from a bare captured name; shortest still breaks
ties, so the order stays total and the verdict deterministic.
* The JS fact file had NO sanitizers at all, so no JavaScript fix of any
family could ever be recognised. Added the documented path-normalisation
and HTML-escaping APIs, with provenance.
* Adding them regressed the witness, because `resolveUrl` CONTAINS `resolve`
and the substring test marked the vulnerable flow sanitized. This is the
same bug class already fixed in dominance.sc and not carried across -- the
exact fix-the-instance-miss-the-class failure. taint.sc now matches on word
boundaries too.
And the principled rule the fix turns on: parameter sources are a FALLBACK,
never an override. When a modelled source reaches the sink, those flows are the
evidence; otherwise a captured `res` reaching a sanitized sink reports the fix
as still vulnerable on a flow that names no attacker input.
Also recorded: req.url was NOT wrong as a diagnosis, it was untestable in
isolation -- the scoping bug masked it. Both were needed. On the pair that
motivated all of this:
vuln model_entailed req.url.split('?')[0] -> readFileSync(possibleFilename)
fixed model_corroborated same flow, sanitized by path.normalize
distinguished: true
700 passing, mypy/ruff clean, gates byte-identical.
Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01T7XD7x5KonMdmGRkp63EQG