https://github.com/trusteddomainproject/OpenDMARC/issues/183
https://bugs.gentoo.org/900521

--- a/opendmarc/opendmarc-arcseal.h	2021-04-30 17:34:43.000000000 +0100
+++ b/opendmarc/opendmarc-arcseal.h	2021-06-25 14:23:01.725593770 +0100
@@ -32,7 +32,7 @@
 /* max header tag value length (short) */
 #define OPENDMARC_ARCSEAL_MAX_SHORT_VALUE_LEN 256
 /* max header tag value length (long) */
-#define OPENDMARC_ARCSEAL_MAX_LONG_VALUE_LEN  512
+#define OPENDMARC_ARCSEAL_MAX_LONG_VALUE_LEN  768
 
 /* names and field labels */
 #define OPENDMARC_ARCSEAL_HDRNAME	"ARC-Seal"
--- a/opendmarc/opendmarc-arcseal.c	2021-04-30 17:34:43.000000000 +0100
+++ b/opendmarc/opendmarc-arcseal.c	2021-06-25 14:27:10.689908703 +0100
@@ -29,7 +29,7 @@
 #include "opendmarc.h"
 
 #define OPENDMARC_ARCSEAL_MAX_FIELD_NAME_LEN 255
-#define OPENDMARC_ARCSEAL_MAX_TOKEN_LEN      512
+#define OPENDMARC_ARCSEAL_MAX_TOKEN_LEN      768
 
 /* tables */
 struct opendmarc_arcseal_lookup
@@ -167,7 +167,12 @@ opendmarc_arcseal_parse(u_char *hdr, str
 		if (*token_ptr == '\0')
 			return 0;
 		tag_label = strsep(&token_ptr, "=");
+		if (token_ptr == NULL)
+			return 0;
+
 		tag_value = opendmarc_arcseal_strip_whitespace(token_ptr);
+		if (tag_value == NULL)
+			return 0;
 
 		tag_code = opendmarc_arcseal_convert(as_tags, tag_label);