Fix O(n^2) CPU exhaustion in parse_link_text (GHSA patch)

Author: bhanugoudm041

src/mistune/helpers.py

@@ -115,6 +115,7 @@ def parse_link_text(src: str, pos: int) -> Union[Tuple[str, int], Tuple[None, No
     while pos < len(src):
         m = _INLINE_SQUARE_BRACKET_RE.search(src, pos)
         if not m:
+            pos = len(src)  # ← CHANGE 1: record we scanned to end
             break
 
         pos = m.end()
@@ -130,7 +131,7 @@ def parse_link_text(src: str, pos: int) -> Union[Tuple[str, int], Tuple[None, No
     if found:
         text = src[start_pos : pos - 1]
         return text, pos
-    return None, None
+    return None, pos  # ← CHANGE 2: return pos instead of None
 
 
 def parse_link_label(src: str, start_pos: int) -> Union[Tuple[str, int], Tuple[None, None]]:

src/mistune/inline_parser.py

@@ -128,7 +128,11 @@ def parse_link(self, m: Match[str], state: InlineState) -> Optional[int]:
         if label is None:
             text, end_pos = parse_link_text(state.src, pos)
             if text is None:
-                return None
+                # ← CHANGE: emit skipped content as literal text
+                # so nothing is dropped, then jump ahead to end_pos
+                skipped = state.src[m.start():end_pos]
+                state.append_token({"type": "text", "raw": skipped})
+                return end_pos
 
         assert end_pos is not None