From <http://seclists.org/fulldisclosure/2016/May/10>.

From 6f0af3f6b9b1c5f82a2bb5ded65923437fee5d21 Mon Sep 17 00:00:00 2001
From: Peter Simons <psimons () suse com>
Date: Fri, 15 Apr 2016 11:56:55 +0200
Subject: [PATCH 2/2] Add missing increments of recursion depth counter to XML
 parser.

The functions xmlParserEntityCheck() and xmlParseAttValueComplex() used to call
xmlStringDecodeEntities() in a recursive context without incrementing the
'depth' counter in the parser context. Because of that omission, the parser
failed to detect attribute recursions in certain documents before running out
of stack space.
---
 parser.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/parser.c b/parser.c
index 9604a72..4da151f 100644
--- a/parser.c
+++ b/parser.c
@@ -144,8 +144,10 @@ xmlParserEntityCheck(xmlParserCtxtPtr ctxt, size_t size,
 
 	ent->checked = 1;
 
+        ++ctxt->depth;
 	rep = xmlStringDecodeEntities(ctxt, ent->content,
 				  XML_SUBSTITUTE_REF, 0, 0, 0);
+        --ctxt->depth;
 
 	ent->checked = (ctxt->nbentities - oldnbent + 1) * 2;
 	if (rep != NULL) {
@@ -3966,8 +3968,10 @@ xmlParseEntityValue(xmlParserCtxtPtr ctxt, xmlChar **orig) {
 	 * an entity declaration, it is bypassed and left as is.
 	 * so XML_SUBSTITUTE_REF is not set here.
 	 */
+        ++ctxt->depth;
 	ret = xmlStringDecodeEntities(ctxt, buf, XML_SUBSTITUTE_PEREF,
 				      0, 0, 0);
+        --ctxt->depth;
 	if (orig != NULL)
 	    *orig = buf;
 	else
@@ -4092,9 +4096,11 @@ xmlParseAttValueComplex(xmlParserCtxtPtr ctxt, int *attlen, int normalize) {
 		} else if ((ent != NULL) &&
 		           (ctxt->replaceEntities != 0)) {
 		    if (ent->etype != XML_INTERNAL_PREDEFINED_ENTITY) {
+			++ctxt->depth;
 			rep = xmlStringDecodeEntities(ctxt, ent->content,
 						      XML_SUBSTITUTE_REF,
 						      0, 0, 0);
+			--ctxt->depth;
 			if (rep != NULL) {
 			    current = rep;
 			    while (*current != 0) { /* non input consuming */
@@ -4130,8 +4136,10 @@ xmlParseAttValueComplex(xmlParserCtxtPtr ctxt, int *attlen, int normalize) {
 			(ent->content != NULL) && (ent->checked == 0)) {
 			unsigned long oldnbent = ctxt->nbentities;
 
+			++ctxt->depth;
 			rep = xmlStringDecodeEntities(ctxt, ent->content,
 						  XML_SUBSTITUTE_REF, 0, 0, 0);
+			--ctxt->depth;
 
 			ent->checked = (ctxt->nbentities - oldnbent + 1) * 2;
 			if (rep != NULL) {
-- 
2.8.1
