A bounds check of %N format on Windows.
Thanks to Joe Bialek, Adam Zabrocki and Microsoft Vulnerability Research.

src/core/ngx_string.c

diff --git a/src/core/ngx_string.c b/src/core/ngx_string.c
index a41c38d..f8641b7 100644
--- a/src/core/ngx_string.c
+++ b/src/core/ngx_string.c
@@ -429,8 +429,12 @@
             case 'N':
 #if (NGX_WIN32)
                 *buf++ = CR;
-#endif
+                if (buf < last) {
+                    *buf++ = LF;
+                }
+#else
                 *buf++ = LF;
+#endif
                 fmt++;
 
                 continue;