diff --git a/ext/commonmarker/arena.c b/ext/commonmarker/arena.c
index 6373c0d0..da1a70e9 100644
--- a/ext/commonmarker/arena.c
+++ b/ext/commonmarker/arena.c
@@ -99,6 +99,6 @@ static void arena_free(void *ptr) {
 
 cmark_mem CMARK_ARENA_MEM_ALLOCATOR = {arena_calloc, arena_realloc, arena_free};
 
-cmark_mem *cmark_get_arena_mem_allocator() {
+cmark_mem *cmark_get_arena_mem_allocator(void) {
   return &CMARK_ARENA_MEM_ALLOCATOR;
 }
diff --git a/ext/commonmarker/autolink.c b/ext/commonmarker/autolink.c
index f3b75a7e..491d96c3 100644
--- a/ext/commonmarker/autolink.c
+++ b/ext/commonmarker/autolink.c
@@ -267,6 +267,11 @@ static cmark_node *url_match(cmark_parser *parser, cmark_node *parent,
   cmark_node *text = cmark_node_new_with_mem(CMARK_NODE_TEXT, parser->mem);
   text->as.literal = url;
   cmark_node_append_child(node, text);
+  
+  node->start_line = text->start_line = node->end_line = text->end_line = cmark_inline_parser_get_line(inline_parser);
+
+  node->start_column = text->start_column = max_rewind - rewind;
+  node->end_column = text->end_column = cmark_inline_parser_get_column(inline_parser) - 1;
 
   return node;
 }
diff --git a/ext/commonmarker/cmark-gfm-core-extensions.h b/ext/commonmarker/cmark-gfm-core-extensions.h
index 0645915f..bc29ffd4 100644
--- a/ext/commonmarker/cmark-gfm-core-extensions.h
+++ b/ext/commonmarker/cmark-gfm-core-extensions.h
@@ -6,45 +6,45 @@ extern "C" {
 #endif
 
 #include "cmark-gfm-extension_api.h"
-#include "cmark-gfm-extensions_export.h"
-#include "config.h" // for bool
+#include "cmark-gfm_export.h"
+#include <stdbool.h>
 #include <stdint.h>
 
-CMARK_GFM_EXTENSIONS_EXPORT
+CMARK_GFM_EXPORT
 void cmark_gfm_core_extensions_ensure_registered(void);
 
-CMARK_GFM_EXTENSIONS_EXPORT
+CMARK_GFM_EXPORT
 uint16_t cmark_gfm_extensions_get_table_columns(cmark_node *node);
 
 /** Sets the number of columns for the table, returning 1 on success and 0 on error.
  */
-CMARK_GFM_EXTENSIONS_EXPORT
+CMARK_GFM_EXPORT
 int cmark_gfm_extensions_set_table_columns(cmark_node *node, uint16_t n_columns);
 
-CMARK_GFM_EXTENSIONS_EXPORT
+CMARK_GFM_EXPORT
 uint8_t *cmark_gfm_extensions_get_table_alignments(cmark_node *node);
 
 /** Sets the alignments for the table, returning 1 on success and 0 on error.
  */
-CMARK_GFM_EXTENSIONS_EXPORT
+CMARK_GFM_EXPORT
 int cmark_gfm_extensions_set_table_alignments(cmark_node *node, uint16_t ncols, uint8_t *alignments);
 
-CMARK_GFM_EXTENSIONS_EXPORT
+CMARK_GFM_EXPORT
 int cmark_gfm_extensions_get_table_row_is_header(cmark_node *node);
 
 /** Sets whether the node is a table header row, returning 1 on success and 0 on error.
  */
-CMARK_GFM_EXTENSIONS_EXPORT
+CMARK_GFM_EXPORT
 int cmark_gfm_extensions_set_table_row_is_header(cmark_node *node, int is_header);
 
-CMARK_GFM_EXTENSIONS_EXPORT
+CMARK_GFM_EXPORT
 bool cmark_gfm_extensions_get_tasklist_item_checked(cmark_node *node);
 /* For backwards compatibility */
 #define cmark_gfm_extensions_tasklist_is_checked cmark_gfm_extensions_get_tasklist_item_checked
 
 /** Sets whether a tasklist item is "checked" (completed), returning 1 on success and 0 on error.
  */
-CMARK_GFM_EXTENSIONS_EXPORT
+CMARK_GFM_EXPORT
 int cmark_gfm_extensions_set_tasklist_item_checked(cmark_node *node, bool is_checked);
 
 #ifdef __cplusplus
diff --git a/ext/commonmarker/cmark-gfm.h b/ext/commonmarker/cmark-gfm.h
index 6fb28693..6b362a86 100644
--- a/ext/commonmarker/cmark-gfm.h
+++ b/ext/commonmarker/cmark-gfm.h
@@ -111,13 +111,13 @@ typedef struct cmark_mem {
  * realloc and free.
  */
 CMARK_GFM_EXPORT
-cmark_mem *cmark_get_default_mem_allocator();
+cmark_mem *cmark_get_default_mem_allocator(void);
 
 /** An arena allocator; uses system calloc to allocate large
  * slabs of memory.  Memory in these slabs is not reused at all.
  */
 CMARK_GFM_EXPORT
-cmark_mem *cmark_get_arena_mem_allocator();
+cmark_mem *cmark_get_arena_mem_allocator(void);
 
 /** Resets the arena allocator, quickly returning all used memory
  * to the operating system.
@@ -225,6 +225,11 @@ CMARK_GFM_EXPORT cmark_node *cmark_node_first_child(cmark_node *node);
  */
 CMARK_GFM_EXPORT cmark_node *cmark_node_last_child(cmark_node *node);
 
+/** Returns the footnote reference of 'node', or NULL if 'node' doesn't have a
+ * footnote reference.
+ */
+CMARK_GFM_EXPORT cmark_node *cmark_node_parent_footnote_def(cmark_node *node);
+
 /**
  * ## Iterator
  *
diff --git a/ext/commonmarker/cmark-upstream b/ext/commonmarker/cmark-upstream
index 57d5e093..c32ef78b 160000
--- a/ext/commonmarker/cmark-upstream
+++ b/ext/commonmarker/cmark-upstream
@@ -1 +1 @@
-Subproject commit 57d5e093ef801f54bf4174c900f7a863599bb47d
+Subproject commit c32ef78bae851cb83b7ad52d0fbff880acdcd44a
diff --git a/ext/commonmarker/cmark.c b/ext/commonmarker/cmark.c
index b3fad4b0..68c40c47 100644
--- a/ext/commonmarker/cmark.c
+++ b/ext/commonmarker/cmark.c
@@ -10,9 +10,9 @@
 cmark_node_type CMARK_NODE_LAST_BLOCK = CMARK_NODE_FOOTNOTE_DEFINITION;
 cmark_node_type CMARK_NODE_LAST_INLINE = CMARK_NODE_FOOTNOTE_REFERENCE;
 
-int cmark_version() { return CMARK_GFM_VERSION; }
+int cmark_version(void) { return CMARK_GFM_VERSION; }
 
-const char *cmark_version_string() { return CMARK_GFM_VERSION_STRING; }
+const char *cmark_version_string(void) { return CMARK_GFM_VERSION_STRING; }
 
 static void *xcalloc(size_t nmem, size_t size) {
   void *ptr = calloc(nmem, size);
@@ -38,7 +38,7 @@ static void xfree(void *ptr) {
 
 cmark_mem CMARK_DEFAULT_MEM_ALLOCATOR = {xcalloc, xrealloc, xfree};
 
-cmark_mem *cmark_get_default_mem_allocator() {
+cmark_mem *cmark_get_default_mem_allocator(void) {
   return &CMARK_DEFAULT_MEM_ALLOCATOR;
 }
 
diff --git a/ext/commonmarker/html.c b/ext/commonmarker/html.c
index 12d3c3e9..529e0ea3 100644
--- a/ext/commonmarker/html.c
+++ b/ext/commonmarker/html.c
@@ -63,10 +63,16 @@ static bool S_put_footnote_backref(cmark_html_renderer *renderer, cmark_strbuf *
   if (renderer->written_footnote_ix >= renderer->footnote_ix)
     return false;
   renderer->written_footnote_ix = renderer->footnote_ix;
+  char m[32];
+  snprintf(m, sizeof(m), "%d", renderer->written_footnote_ix);
 
   cmark_strbuf_puts(html, "<a href=\"#fnref-");
   houdini_escape_href(html, node->as.literal.data, node->as.literal.len);
-  cmark_strbuf_puts(html, "\" class=\"footnote-backref\" data-footnote-backref aria-label=\"Back to content\">↩</a>");
+  cmark_strbuf_puts(html, "\" class=\"footnote-backref\" data-footnote-backref data-footnote-backref-idx=\"");
+  cmark_strbuf_puts(html, m);
+  cmark_strbuf_puts(html, "\" aria-label=\"Back to reference ");
+  cmark_strbuf_puts(html, m);
+  cmark_strbuf_puts(html, "\">↩</a>");
 
   if (node->footnote.def_count > 1)
   {
@@ -78,7 +84,15 @@ static bool S_put_footnote_backref(cmark_html_renderer *renderer, cmark_strbuf *
       houdini_escape_href(html, node->as.literal.data, node->as.literal.len);
       cmark_strbuf_puts(html, "-");
       cmark_strbuf_puts(html, n);
-      cmark_strbuf_puts(html, "\" class=\"footnote-backref\" data-footnote-backref aria-label=\"Back to content\">↩<sup class=\"footnote-ref\">");
+      cmark_strbuf_puts(html, "\" class=\"footnote-backref\" data-footnote-backref data-footnote-backref-idx=\"");
+      cmark_strbuf_puts(html, m);
+      cmark_strbuf_puts(html, "-");
+      cmark_strbuf_puts(html, n);
+      cmark_strbuf_puts(html, "\" aria-label=\"Back to reference ");
+      cmark_strbuf_puts(html, m);
+      cmark_strbuf_puts(html, "-");
+      cmark_strbuf_puts(html, n);
+      cmark_strbuf_puts(html, "\">↩<sup class=\"footnote-ref\">");
       cmark_strbuf_puts(html, n);
       cmark_strbuf_puts(html, "</sup></a>");
     }
diff --git a/ext/commonmarker/node.c b/ext/commonmarker/node.c
index 80c434e3..56daf0aa 100644
--- a/ext/commonmarker/node.c
+++ b/ext/commonmarker/node.c
@@ -9,12 +9,8 @@ static void S_node_unlink(cmark_node *node);
 
 #define NODE_MEM(node) cmark_node_mem(node)
 
-cmark_node__internal_flags CMARK_NODE__OPEN;
-cmark_node__internal_flags CMARK_NODE__LAST_LINE_BLANK;
-cmark_node__internal_flags CMARK_NODE__LAST_LINE_CHECKED;
-
-void cmark_register_node_flag(cmark_node__internal_flags *flags) {
-  static uint8_t shift = 0;
+void cmark_register_node_flag(cmark_node_internal_flags *flags) {
+  static cmark_node_internal_flags nextflag = CMARK_NODE__REGISTER_FIRST;
 
   // flags should be a pointer to a global variable and this function
   // should only be called once to initialize its value.
@@ -24,24 +20,16 @@ void cmark_register_node_flag(cmark_node__internal_flags *flags) {
   }
 
   // Check that we haven't run out of bits.
-  if (shift >= 8 * sizeof(cmark_node__internal_flags)) {
+  if (nextflag == 0) {
     fprintf(stderr, "too many flags in cmark_register_node_flag\n");
     abort();
   }
 
-  *flags = (cmark_node__internal_flags)1 << shift;
-  shift++;
+  *flags = nextflag;
+  nextflag <<= 1;
 }
 
-void cmark_init_standard_node_flags() {
-  static int initialized = 0;
-  if (!initialized) {
-    initialized = 1;
-    cmark_register_node_flag(&CMARK_NODE__OPEN);
-    cmark_register_node_flag(&CMARK_NODE__LAST_LINE_BLANK);
-    cmark_register_node_flag(&CMARK_NODE__LAST_LINE_CHECKED);
-  }
-}
+void cmark_init_standard_node_flags() {}
 
 bool cmark_node_can_contain_type(cmark_node *node, cmark_node_type child_type) {
   if (child_type == CMARK_NODE_DOCUMENT) {
@@ -335,6 +323,14 @@ cmark_node *cmark_node_last_child(cmark_node *node) {
   }
 }
 
+cmark_node *cmark_node_parent_footnote_def(cmark_node *node) {
+  if (node == NULL) {
+    return NULL;
+  } else {
+    return node->parent_footnote_def;
+  }
+}
+
 void *cmark_node_get_user_data(cmark_node *node) {
   if (node == NULL) {
     return NULL;
diff --git a/ext/commonmarker/node.h b/ext/commonmarker/node.h
index 281258f7..e025e25d 100644
--- a/ext/commonmarker/node.h
+++ b/ext/commonmarker/node.h
@@ -48,7 +48,17 @@ typedef struct {
   cmark_chunk on_exit;
 } cmark_custom;
 
-typedef uint16_t cmark_node__internal_flags;
+enum cmark_node__internal_flags {
+  CMARK_NODE__OPEN = (1 << 0),
+  CMARK_NODE__LAST_LINE_BLANK = (1 << 1),
+  CMARK_NODE__LAST_LINE_CHECKED = (1 << 2),
+
+  // Extensions can register custom flags by calling `cmark_register_node_flag`.
+  // This is the starting value for the custom flags.
+  CMARK_NODE__REGISTER_FIRST = (1 << 3),
+};
+
+typedef uint16_t cmark_node_internal_flags;
 
 struct cmark_node {
   cmark_strbuf content;
@@ -68,7 +78,7 @@ struct cmark_node {
   int end_column;
   int internal_offset;
   uint16_t type;
-  cmark_node__internal_flags flags;
+  cmark_node_internal_flags flags;
 
   cmark_syntax_extension *extension;
 
@@ -98,19 +108,15 @@ struct cmark_node {
  * which will store the flag value.
  */
 CMARK_GFM_EXPORT
-void cmark_register_node_flag(cmark_node__internal_flags *flags);
-
-/**
- * Standard node flags. (Initialized using `cmark_init_standard_node_flags`.)
- */
-extern cmark_node__internal_flags CMARK_NODE__OPEN;
-extern cmark_node__internal_flags CMARK_NODE__LAST_LINE_BLANK;
-extern cmark_node__internal_flags CMARK_NODE__LAST_LINE_CHECKED;
+void cmark_register_node_flag(cmark_node_internal_flags *flags);
 
 /**
- * Uses `cmark_register_node_flag` to initialize the standard node flags.
- * This function should be called at program startup time. Calling it
- * multiple times has no additional effect.
+ * DEPRECATED.
+ *
+ * This function was added in cmark-gfm version 0.29.0.gfm.7, and was
+ * required to be called at program start time, which caused
+ * backwards-compatibility issues in applications that use cmark-gfm as a
+ * library. It is now a no-op.
  */
 CMARK_GFM_EXPORT
 void cmark_init_standard_node_flags();
diff --git a/ext/commonmarker/table.c b/ext/commonmarker/table.c
index 7f281322..e53ea315 100644
--- a/ext/commonmarker/table.c
+++ b/ext/commonmarker/table.c
@@ -12,7 +12,7 @@
 #include "cmark-gfm-core-extensions.h"
 
 // Custom node flag, initialized in `create_table_extension`.
-static cmark_node__internal_flags CMARK_NODE__TABLE_VISITED;
+static cmark_node_internal_flags CMARK_NODE__TABLE_VISITED;
 
 cmark_node_type CMARK_NODE_TABLE, CMARK_NODE_TABLE_ROW,
     CMARK_NODE_TABLE_CELL;
diff --git a/lib/commonmarker/version.rb b/lib/commonmarker/version.rb
index 7d03a7ea..6405511f 100644
--- a/lib/commonmarker/version.rb
+++ b/lib/commonmarker/version.rb
@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module CommonMarker
-  VERSION = "0.23.7"
+  VERSION = "0.23.8"
 end
diff --git a/test/test_footnotes.rb b/test/test_footnotes.rb
index 7cdfd93a..0e00a913 100644
--- a/test/test_footnotes.rb
+++ b/test/test_footnotes.rb
@@ -13,7 +13,7 @@ def test_to_html
       <section class="footnotes" data-footnotes>
       <ol>
       <li id="fn-hi">
-      <p>Hey! <a href="#fnref-hi" class="footnote-backref" data-footnote-backref aria-label="Back to content">↩</a></p>
+      <p>Hey! <a href="#fnref-hi" class="footnote-backref" data-footnote-backref data-footnote-backref-idx="1" aria-label="Back to reference 1">↩</a></p>
       </li>
       </ol>
       </section>
@@ -50,7 +50,7 @@ def test_render_html
       <section class="footnotes" data-footnotes>
       <ol>
       <li id="fn-1">
-      <p>This is a footnote <a href="#fnref-1" class="footnote-backref" data-footnote-backref aria-label="Back to content">↩</a></p>
+      <p>This is a footnote <a href="#fnref-1" class="footnote-backref" data-footnote-backref data-footnote-backref-idx="1" aria-label="Back to reference 1">↩</a></p>
       </li>
       </ol>
       </section>