diff --git a/src/libopensc/asn1.c b/src/libopensc/asn1.c
index f1424029..d70d0319 100644
--- a/src/libopensc/asn1.c
+++ b/src/libopensc/asn1.c
@@ -364,7 +364,7 @@ static void print_tags_recursive(const u8 * buf0, const u8 * buf,
 		size_t len;
 
 		r = sc_asn1_read_tag(&tagp, bytesleft, &cla, &tag, &len);
-		if (r != SC_SUCCESS) {
+		if (r != SC_SUCCESS || tagp == NULL) {
 			printf("Error in decoding.\n");
 			return;
 		}
@@ -475,8 +475,10 @@ const u8 *sc_asn1_find_tag(sc_context_t *ctx, const u8 * buf,
 
 		buf = p;
 		/* read a tag */
-		if (sc_asn1_read_tag(&p, left, &cla, &tag, &taglen) != SC_SUCCESS)
+		if (sc_asn1_read_tag(&p, left, &cla, &tag, &taglen) != SC_SUCCESS
+				|| p == NULL)
 			return NULL;
+
 		left -= (p - buf);
 		/* we need to shift the class byte to the leftmost
 		 * byte of the tag */
@@ -506,7 +508,8 @@ const u8 *sc_asn1_skip_tag(sc_context_t *ctx, const u8 ** buf, size_t *buflen,
 	size_t len = *buflen, taglen;
 	unsigned int cla = 0, tag;
 
-	if (sc_asn1_read_tag((const u8 **) &p, len, &cla, &tag, &taglen) != SC_SUCCESS)
+	if (sc_asn1_read_tag((const u8 **) &p, len, &cla, &tag, &taglen) != SC_SUCCESS
+			|| p == NULL)
 		return NULL;
 	switch (cla & 0xC0) {
 	case SC_ASN1_TAG_UNIVERSAL:
diff --git a/src/libopensc/card-gids.c b/src/libopensc/card-gids.c
index 34b4ce75..d8bcb885 100644
--- a/src/libopensc/card-gids.c
+++ b/src/libopensc/card-gids.c
@@ -533,17 +533,19 @@ static int gids_get_pin_status(sc_card_t *card, int pinreference, int *tries_lef
 	r = gids_get_DO(card, GIDS_APPLET_EFID, dataObjectIdentifier, buffer, &buffersize);
 	SC_TEST_RET(card->ctx, SC_LOG_DEBUG_NORMAL, r, "unable to update the masterfile");
 
-	p = sc_asn1_find_tag(card->ctx, buffer, sizeof(buffer), GIDS_TRY_COUNTER_OLD_TAG, &datasize);
+	buffersize = buffersize > sizeof(buffer) ? sizeof(buffer) : buffersize;
+
+	p = sc_asn1_find_tag(card->ctx, buffer, buffersize, GIDS_TRY_COUNTER_OLD_TAG, &datasize);
 	if (p && datasize == 1) {
 		if (tries_left)
 			*tries_left = p[0];
 	}
-	p = sc_asn1_find_tag(card->ctx, buffer, sizeof(buffer), GIDS_TRY_COUNTER_TAG, &datasize);
+	p = sc_asn1_find_tag(card->ctx, buffer, buffersize, GIDS_TRY_COUNTER_TAG, &datasize);
 	if (p && datasize == 1) {
 		if (tries_left)
 			*tries_left = p[0];
 	}
-	p = sc_asn1_find_tag(card->ctx, buffer, sizeof(buffer), GIDS_TRY_LIMIT_TAG, &datasize);
+	p = sc_asn1_find_tag(card->ctx, buffer, buffersize , GIDS_TRY_LIMIT_TAG, &datasize);
 	if (p && datasize == 1) {
 		if (tries_left)
 			*max_tries = p[0];
diff --git a/src/libopensc/card-mcrd.c b/src/libopensc/card-mcrd.c
index 57ead6bd..2923d1f5 100644
--- a/src/libopensc/card-mcrd.c
+++ b/src/libopensc/card-mcrd.c
@@ -606,8 +606,8 @@ static void process_arr(sc_card_t * card, sc_file_t * file,
 	skip = 1;		/* Skip over initial unknown SC DOs. */
 	for (;;) {
 		buf = p;
-		if (sc_asn1_read_tag(&p, left, &cla, &tag, &taglen) !=
-		    SC_SUCCESS)
+		if (sc_asn1_read_tag(&p, left, &cla, &tag, &taglen) != SC_SUCCESS
+				|| p == NULL)
 			break;
 		left -= (p - buf);
 		tag |= cla;
diff --git a/src/libopensc/card-openpgp.c b/src/libopensc/card-openpgp.c
index 55c19395..bfb00149 100644
--- a/src/libopensc/card-openpgp.c
+++ b/src/libopensc/card-openpgp.c
@@ -922,7 +922,7 @@ pgp_enumerate_blob(sc_card_t *card, pgp_blob_t *blob)
 
 		r = sc_asn1_read_tag(&data, blob->len - (in - blob->data),
 					&cla, &tag, &len);
-		if (r < 0) {
+		if (r < 0 || data == NULL) {
 			sc_debug(card->ctx, SC_LOG_DEBUG_NORMAL,
 				 "Unexpected end of contents\n");
 			return SC_ERROR_OBJECT_NOT_VALID;
@@ -2132,6 +2132,8 @@ pgp_parse_and_set_pubkey_output(sc_card_t *card, u8* data, size_t data_len,
 		r = sc_asn1_read_tag((const u8**)&part,
 							 data_len - (in - data),
 							 &cla, &tag, &len);
+		if (part == NULL)
+			r = SC_ERROR_ASN1_OBJECT_NOT_FOUND;
 		LOG_TEST_RET(card->ctx, r, "Unexpected end of contents.");
 		/* undo ASN1's split of tag & class */
 		for (tmptag = tag; tmptag > 0x0FF; tmptag >>= 8) {
diff --git a/src/libopensc/card-piv.c b/src/libopensc/card-piv.c
index c291374d..70fbd660 100644
--- a/src/libopensc/card-piv.c
+++ b/src/libopensc/card-piv.c
@@ -573,7 +573,8 @@ static int piv_general_io(sc_card_t *card, int ins, int p1, int p2,
 		 * the buffer is bigger, so it will not produce "ASN1.tag too long!" */
 
 		body = rbuf;
-		if (sc_asn1_read_tag(&body, 0xffff, &cla_out, &tag_out, &bodylen) !=  SC_SUCCESS)  {
+		if (sc_asn1_read_tag(&body, 0xffff, &cla_out, &tag_out, &bodylen) !=  SC_SUCCESS
+				|| body == NULL)  {
 			/* only early beta cards had this problem */
 			sc_log(card->ctx, "***** received buffer tag MISSING ");
 			body = rbuf;
@@ -679,6 +680,9 @@ static int piv_generate_key(sc_card_t *card,
 		in_len = rbuflen;
 
 		r = sc_asn1_read_tag(&cp, rbuflen, &cla_out, &tag_out, &in_len);
+		if (cp == NULL) {
+			r = SC_ERROR_ASN1_OBJECT_NOT_FOUND;
+		}
 		if (r != SC_SUCCESS) {
 			sc_log(card->ctx, "Tag buffer not found");
 			goto err;
@@ -881,7 +885,8 @@ static int piv_read_obj_from_file(sc_card_t * card, char * filename,
 		goto err;
 	}
 	body = tagbuf;
-	if (sc_asn1_read_tag(&body, 0xfffff, &cla_out, &tag_out, &bodylen) != SC_SUCCESS) {
+	if (sc_asn1_read_tag(&body, 0xfffff, &cla_out, &tag_out, &bodylen) != SC_SUCCESS
+			|| body == NULL) {
 		sc_log(card->ctx, "DER problem");
 		r = SC_ERROR_INVALID_ASN1_OBJECT;
 		goto err;
@@ -947,7 +952,8 @@ piv_get_data(sc_card_t * card, int enumtag, u8 **buf, size_t *buf_len)
 		r = piv_general_io(card, 0xCB, 0x3F, 0xFF, tagbuf,  p - tagbuf, &rbuf, &rbuflen);
 		if (r > 0) {
 			body = rbuf;
-			if (sc_asn1_read_tag(&body, 0xffff, &cla_out, &tag_out, &bodylen) !=  SC_SUCCESS) {
+			if (sc_asn1_read_tag(&body, 0xffff, &cla_out, &tag_out, &bodylen) !=  SC_SUCCESS
+					|| body == NULL) {
 				sc_log(card->ctx, "***** received buffer tag MISSING ");
 				r = SC_ERROR_FILE_NOT_FOUND;
 				goto err;
@@ -2847,8 +2853,8 @@ piv_process_history(sc_card_t *card)
 
 		body = ocfhfbuf;
 		if (sc_asn1_read_tag(&body, ocfhflen, &cla_out,
-				&tag_out, &bodylen) != SC_SUCCESS ||
-				cla_out+tag_out != 0x30) {
+					&tag_out, &bodylen) != SC_SUCCESS
+				|| cla_out+tag_out != 0x30) {
 			sc_log(card->ctx, "DER problem");
 			r = SC_ERROR_INVALID_ASN1_OBJECT;
 			goto err;
@@ -2857,8 +2863,8 @@ piv_process_history(sc_card_t *card)
 		while (bodylen > 0) {
 			seqtag = seq;
 			if (sc_asn1_read_tag(&seq, bodylen, &cla_out,
-					&tag_out, &seqlen) != SC_SUCCESS ||
-					cla_out+tag_out != 0x30) {
+						&tag_out, &seqlen) != SC_SUCCESS
+					|| cla_out+tag_out != 0x30) {
 				sc_log(card->ctx, "DER problem");
 				r = SC_ERROR_INVALID_ASN1_OBJECT;
 				goto err;
diff --git a/src/libopensc/ef-gdo.c b/src/libopensc/ef-gdo.c
index bda51f22..39dea2e5 100644
--- a/src/libopensc/ef-gdo.c
+++ b/src/libopensc/ef-gdo.c
@@ -47,7 +47,7 @@ sc_parse_ef_gdo_content(const unsigned char *gdo, size_t gdo_len,
 			}
 			break;
 		}
-		if (tag == SC_ASN1_TAG_EOC) {
+		if (p == NULL) {
 			/* done parsing */
 			break;
 		}
diff --git a/src/libopensc/iso7816.c b/src/libopensc/iso7816.c
index a8c12b51..df283d20 100644
--- a/src/libopensc/iso7816.c
+++ b/src/libopensc/iso7816.c
@@ -343,7 +343,8 @@ iso7816_process_fci(struct sc_card *card, struct sc_file *file,
 			p < end;
 			p += length, length = end - p) {
 
-		if (SC_SUCCESS != sc_asn1_read_tag(&p, length, &cla, &tag, &length)) {
+		if (SC_SUCCESS != sc_asn1_read_tag(&p, length, &cla, &tag, &length)
+				|| p == NULL) {
 			break;
 		}
 		switch (cla | tag) {
diff --git a/src/libopensc/pkcs15-pubkey.c b/src/libopensc/pkcs15-pubkey.c
index 1d54dbe2..0be05bf7 100644
--- a/src/libopensc/pkcs15-pubkey.c
+++ b/src/libopensc/pkcs15-pubkey.c
@@ -1269,7 +1269,7 @@ sc_pkcs15_read_der_file(sc_context_t *ctx, char * filename,
 	if (r != SC_SUCCESS && r != SC_ERROR_ASN1_END_OF_CONTENTS)
 		goto out;
 
-	if (tag_out == SC_ASN1_TAG_EOC || body == NULL)   {
+	if (body == NULL)   {
 		r = SC_SUCCESS;
 		goto out;
 	}
diff --git a/src/pkcs15init/pkcs15-myeid.c b/src/pkcs15init/pkcs15-myeid.c
index 4931027d..29f9aa22 100644
--- a/src/pkcs15init/pkcs15-myeid.c
+++ b/src/pkcs15init/pkcs15-myeid.c
@@ -821,6 +821,8 @@ myeid_generate_key(struct sc_profile *profile, struct sc_pkcs15_card *p15card,
 
 			dataptr = data_obj.Data;
 			r = sc_asn1_read_tag((const u8 **)&dataptr, data_obj.DataLen, &cla, &tag, &taglen);
+			if (dataptr == NULL)
+				r = SC_ERROR_ASN1_OBJECT_NOT_FOUND;
 			LOG_TEST_RET(ctx, r, "Invalid EC public key data. Cannot parse DER structure.");
 
 			if (taglen == 0)
diff --git a/src/tools/sc-hsm-tool.c b/src/tools/sc-hsm-tool.c
index 6ae21163..d246b461 100644
--- a/src/tools/sc-hsm-tool.c
+++ b/src/tools/sc-hsm-tool.c
@@ -1223,7 +1223,8 @@ static size_t determineLength(const u8 *tlv, size_t buflen)
 	unsigned int cla,tag;
 	size_t len;
 
-	if (sc_asn1_read_tag(&ptr, buflen, &cla, &tag, &len) != SC_SUCCESS) {
+	if (sc_asn1_read_tag(&ptr, buflen, &cla, &tag, &len) != SC_SUCCESS
+			|| ptr == NULL) {
 		return 0;
 	}
 
@@ -1515,16 +1516,16 @@ static int unwrap_key(sc_card_t *card, int keyid, const char *inf, const char *p
 	fclose(in);
 
 	ptr = keyblob;
-	if ((sc_asn1_read_tag(&ptr, keybloblen, &cla, &tag, &len) != SC_SUCCESS) ||
-			((cla & SC_ASN1_TAG_CONSTRUCTED) != SC_ASN1_TAG_CONSTRUCTED) ||
-			((tag != SC_ASN1_TAG_SEQUENCE)) ){
+	if ((sc_asn1_read_tag(&ptr, keybloblen, &cla, &tag, &len) != SC_SUCCESS)
+		   	|| ((cla & SC_ASN1_TAG_CONSTRUCTED) != SC_ASN1_TAG_CONSTRUCTED)
+		   	|| (tag != SC_ASN1_TAG_SEQUENCE) ){
 		fprintf(stderr, "Invalid wrapped key format (Outer sequence).\n");
 		return -1;
 	}
 
-	if ((sc_asn1_read_tag(&ptr, len, &cla, &tag, &olen) != SC_SUCCESS) ||
-			(cla & SC_ASN1_TAG_CONSTRUCTED) ||
-			((tag != SC_ASN1_TAG_OCTET_STRING)) ){
+	if ((sc_asn1_read_tag(&ptr, len, &cla, &tag, &olen) != SC_SUCCESS)
+		   	|| ((cla & SC_ASN1_TAG_CONSTRUCTED) != SC_ASN1_TAG_CONSTRUCTED)
+		   	|| (tag != SC_ASN1_TAG_OCTET_STRING) ){
 		fprintf(stderr, "Invalid wrapped key format (Key binary).\n");
 		return -1;
 	}