fix(scan): a catch-all function's parameters are not attacker input; field reads need the same field

Two classes the traced PMPro survivors named after 1f91c0b:

- The mapper records every named PHP function as an entry of kind
  `function` (3,507 of PMPro's 4,412), and every entry's parameters were
  sources, so internal helpers became injections: sendCancelAdminEmail's
  $user, a gateway hook callback's $user_id/$morder fired by do_action.
  Regions now carry the entry kind; parameters are input only for request
  entries (route, parser, privileged surface). Call depth is unchanged, so
  such a region is still followed into its callees. JavaScript and Python
  emit no `function` entries.
- The object rule is general: a field read continues a flow through the
  bare object only if the taint came through the SAME field, or was
  assigned to the variable or passed in as a parameter. It now also cuts
  $this->Gateway -> this -> $this->user_id (memberorder.php:705).

plausible() memoises the sink test per node and skips the object walk for
paths with no field access (the filter had cost one outlier 101 s -> 160 s).

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01EmM1j46qgKMh3zqD1QMwEo

src/openultrasast/cpg/queries/taint.sc

@@ -302,12 +302,6 @@
   def fieldOf(c: io.shiftleft.codepropertygraph.generated.nodes.Call): String =
     c.argument.l.find(_.argumentIndex == 2).map(_.code.trim).getOrElse("")
 
-  def writtenField(c: io.shiftleft.codepropertygraph.generated.nodes.Call): Boolean =
-    c.argumentIndex == 1 && (c.astParent match {
-      case parent: io.shiftleft.codepropertygraph.generated.nodes.Call => parent.name == "<operator>.assignment"
-      case _                                                           => false
-    })
-
   def assignedTo(id: io.shiftleft.codepropertygraph.generated.nodes.Identifier): Boolean =
     id.argumentIndex == 1 && (id.astParent match {
       case parent: io.shiftleft.codepropertygraph.generated.nodes.Call => parent.name == "<operator>.assignment"
@@ -324,8 +318,10 @@
           if (j < 0) false // the object itself is where the path starts: it IS the tainted value
           else
             elements(j) match {
-              case prior: io.shiftleft.codepropertygraph.generated.nodes.Call if prior.name == "<operator>.fieldAccess" =>
-                writtenField(prior) && fieldOf(prior) != fieldOf(read)
+              // Through the SAME field -- written then read back, or read and read again -- is field-sensitive.
+              case prior: io.shiftleft.codepropertygraph.generated.nodes.Call
+                  if prior.name == "<operator>.fieldAccess" && fieldOf(prior) == fieldOf(read) =>
+                false
               case _ =>
                 // How did the value reach the object? Legitimately only by being ASSIGNED to it
                 // (`$data = json_decode($input)`) or passed in as a parameter. An object merely used beside
@@ -340,9 +336,21 @@
       }
     }
 
+  // Per element, not per path: the same nodes recur across thousands of paths of one sink, and walking each
+  // path's calls afresh cost one outlier request 101 s -> 160 s.
+  val familySinkMemo = scala.collection.mutable.Map.empty[Long, Boolean]
+
   def plausible(flow: io.joern.dataflowengineoss.language.Path): Boolean = {
     val elements = flow.elements.l
-    !elements.dropRight(1).exists(familySinkCall) && !absorbedByObject(elements)
+    val throughSink = elements.dropRight(1).exists {
+      case c: io.shiftleft.codepropertygraph.generated.nodes.Call if !c.name.startsWith("<operator") =>
+        familySinkMemo.getOrElseUpdate(c.id, familySinkCall(c))
+      case _ => false
+    }
+    !throughSink && !(elements.exists {
+      case c: io.shiftleft.codepropertygraph.generated.nodes.Call => c.name == "<operator>.fieldAccess"
+      case _                                                      => false
+    } && absorbedByObject(elements))
   }
 
   // Framework sources are untrusted wherever they appear. Parameters are untrusted only where the caller has

src/openultrasast/model/regions.py

@@ -66,6 +66,10 @@ class ScanRegion:
     # Does the project's own build declaration name this file? True when it declares nothing at all --
     # silence is not exclusion, and no repository is penalised for a build system we cannot read.
     shipped: bool = True
+    # What the mapper called the entry: `route`, `parser`, `privileged_surface`, ... or `function`, which is
+    # its catch-all for a named function with no evidence of receiving a request. Only the scan's parameter
+    # rule reads it, because only it depends on whether a parameter carries request data.
+    entry_kind: str = ""
 
 
 def regions_for(entries: Sequence[object], targets: Sequence[object], *, shipped: frozenset[str] | None = None) -> tuple[ScanRegion, ...]:
@@ -126,6 +130,7 @@ def regions_for(entries: Sequence[object], targets: Sequence[object], *, shipped
                 families=families,
                 rank=rank,
                 source="module_scope" if module_body else "entry_point",
+                entry_kind=str(getattr(entry, "kind", "") or ""),
             )
 
     # A nameless entry point IS the file. Where a named region already covers that file it adds nothing but

src/openultrasast/model/scan.py

@@ -559,7 +559,7 @@ def _scan_repository_impl(
                 # A repository's parameters are not all attacker input -- but an ENTRY POINT's are, by
                 # definition. That is the trust boundary, and it is the one place both halves of the old
                 # objection stop applying.
-                parameter_sources=_is_entry_point(region),
+                parameter_sources=_parameters_are_input(region),
                 call_depth=ENTRY_POINT_CALL_DEPTH if _is_entry_point(region) else 0,
             )
         except Exception as exc:  # noqa: BLE001 -- one bad region must not end the scan
@@ -1456,7 +1456,7 @@ def _grouped(
                     spec,
                     function=function,
                     file=region.path,
-                    parameter_sources=entry,
+                    parameter_sources=_parameters_are_input(region),
                     call_depth=ENTRY_POINT_CALL_DEPTH if entry else 0,
                     hook_callbacks=hook_callbacks,
                 ),
@@ -1502,6 +1502,20 @@ def _is_entry_point(region: ScanRegion) -> bool:
     return region.source == "entry_point" and bool(region.function) and region.function != MODULE_SCOPE and region.shipped
 
 
+def _parameters_are_input(region: ScanRegion) -> bool:
+    """Are this region's own parameters attacker input? Only where the mapper saw a request arrive.
+
+    `function` is the mapper's catch-all: every named function it found, with no evidence of a request. On a
+    WordPress plugin that is 3,507 of 4,412 entries, and treating their parameters as input made every internal
+    helper a source -- `sendCancelAdminEmail($user, $old_level_id)`, a gateway's
+    `pmpro_checkout_before_change_membership_level($user_id, $morder)` fired by `do_action` with internal ids.
+    Adjudicated on PMPro 2026-09-23, those were false SQL injections. Routes, parsers and privileged surfaces
+    keep the rule; JavaScript and Python emit no `function` entries at all. The region is still followed into
+    its callees -- call depth stays with `_is_entry_point` -- only its parameters stop being sources.
+    """
+    return _is_entry_point(region) and region.entry_kind != "function"
+
+
 def _spec_for(family: str, language: str) -> ArbiterSpec | None:
     """The spec whose arbiter can decide this family. Routing stays a lookup; dispatch stays in `_arbitrate`."""
     if family == "access_control":

tests/test_model_scope.py

@@ -375,3 +375,16 @@ def test_a_killed_culprit_makes_its_family_dearer_and_nothing_else() -> None:
     assert sizer.rate("output_encoding") >= 54.0
     assert abs(sizer.rate("injection") - 1.0) < 1e-9
     assert sizer.fixed == 25.0, "a killed portion must not be read as a fixed-start sample"
+
+
+def test_only_a_request_entry_treats_its_parameters_as_attacker_input() -> None:
+    """The mapper's `function` kind is its catch-all; its parameters carry whatever the caller had."""
+    from openultrasast.model import scan
+
+    route = ScanRegion("api.php", "handle", "php", ("injection",), 1.0, "entry_point", entry_kind="route")
+    helper = ScanRegion("mail.php", "sendCancelAdminEmail", "php", ("injection",), 0.3, "entry_point", entry_kind="function")
+    params = scan._grouped([("0", route, scan._spec_for("injection", "php")), ("1", helper, scan._spec_for("injection", "php"))])["taint"]
+    assert params["0"]["parameterSources"] == "true"
+    assert params["1"]["parameterSources"] == "false"
+    # Still followed into its callees: only its own parameters stop being sources.
+    assert params["1"]["callDepth"] == params["0"]["callDepth"] != "0"