add a "../" removing taint-step for js/path-injection

javascript/ql/src/semmle/javascript/security/dataflow/TaintedPath.qll

@@ -206,6 +206,14 @@ module TaintedPath {
         dstlabel.isNormalized()
       )
       or
+      // foo.replace(/(\.\.\/)*/, "") and similar
+      exists(DotDotSlashPrefixRemovingReplace call |
+        src = call.getInput() and
+        dst = call.getOutput() and
+        dstlabel.isAbsolute() and // result can be absolute
+        dstlabel.toAbsolute() = srclabel.toAbsolute() // preserves normalization status
+      )
+      or
       // path.join()
       exists(DataFlow::CallNode join, int n |
         join = NodeJSLib::Path::moduleMember("join").getACall()

javascript/ql/src/semmle/javascript/security/dataflow/TaintedPathCustomizations.qll

@@ -225,7 +225,8 @@ module TaintedPath {
         term.getAMatchedString() = "/" or
         term.getAMatchedString() = "." or
         term.getAMatchedString() = ".."
-      )
+      ) and
+      not this instanceof DotDotSlashPrefixRemovingReplace
     }
 
     /**
@@ -239,6 +240,57 @@ module TaintedPath {
     DataFlow::Node getOutput() { result = output }
   }
 
+  /**
+   * A call that removes all instances of "../" in the prefix of the string.
+   */
+  class DotDotSlashPrefixRemovingReplace extends DataFlow::CallNode {
+    DataFlow::Node input;
+    DataFlow::Node output;
+
+    DotDotSlashPrefixRemovingReplace() {
+      this.getCalleeName() = "replace" and
+      input = getReceiver() and
+      output = this and
+      exists(RegExpLiteral literal, RegExpTerm term |
+        getArgument(0).getALocalSource().asExpr() = literal and
+        (term instanceof RegExpStar or term instanceof RegExpPlus) and
+        term.getChild(0) = getADotDotSlashMatcher()
+      |
+        literal.getRoot() = term
+        or
+        exists(RegExpSequence seq | seq.getNumChild() = 2 and literal.getRoot() = seq |
+          seq.getChild(0) instanceof RegExpCaret and
+          seq.getChild(1) = term
+        )
+      )
+    }
+
+    /**
+     * Gets the input path to be sanitized.
+     */
+    DataFlow::Node getInput() { result = input }
+
+    /**
+     * Gets the path where prefix "../" has been removed.
+     */
+    DataFlow::Node getOutput() { result = output }
+  }
+
+  /**
+   * Gets a RegExpTerm that matches a variation of "../".
+   */
+  private RegExpTerm getADotDotSlashMatcher() {
+    result.getAMatchedString() = "../"
+    or
+    exists(RegExpSequence seq | seq = result |
+      seq.getChild(0).getConstantValue() = "." and
+      seq.getChild(1).getConstantValue() = "." and
+      seq.getAChild().getAMatchedString() = "/"
+    )
+    or
+    exists(RegExpGroup group | result = group | group.getChild(0) = getADotDotSlashMatcher())
+  }
+
   /**
    * A call that removes all "." or ".." from a path, without also removing all forward slashes.
    */