--- a/gen-pdu/message.c	Sat Aug 05 08:44:32 2023 +0000
+++ b/gen-pdu/message.c	Sat Aug 05 16:55:24 2023 +0000
@@ -111,6 +111,11 @@
 		udh_chars = 0;
 	}
 	plain_chars = input_len - udhl1;
+	if (check_high_bit(input + udhl1, plain_chars) < 0) {
+		fprintf(stderr, ERR_PREFIX "high bit set in GSM7 data\n",
+			input_lineno);
+		exit(1);
+	}
 	udl = udh_chars + plain_chars;
 	if (udl > 160) {
 		fprintf(stderr, ERR_PREFIX

--- a/libcoding/Makefile	Sat Aug 05 08:44:32 2023 +0000
+++ b/libcoding/Makefile	Sat Aug 05 16:55:24 2023 +0000
@@ -1,7 +1,8 @@
 CC=	gcc
 CFLAGS=	-O2
-OBJS=	gsm7_encode.o gsm7_encode_table.o gsm7_pack.o hexdigits.o hexout.o \
-	number_encode.o timestamp.o ucs2_bigend.o utf8_decode.o utf8_decode2.o
+OBJS=	check_high_bit.o gsm7_encode.o gsm7_encode_table.o gsm7_pack.o \
+	hexdigits.o hexout.o number_encode.o timestamp.o ucs2_bigend.o \
+	utf8_decode.o utf8_decode2.o
 LIB=	libcoding.a
 
 all:	${LIB}

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libcoding/check_high_bit.c	Sat Aug 05 16:55:24 2023 +0000
@@ -0,0 +1,20 @@
+/*
+ * The function implemented in this module is intended for validating inputs
+ * that are expected to be in the form of GSM7 characters carried in an octet
+ * string, where the high bit of every octet is expected to be cleared.
+ */
+
+#include <sys/types.h>
+
+check_high_bit(buf, len)
+	u_char *buf;
+	unsigned len;
+{
+	unsigned n;
+
+	for (n = 0; n < len; n++) {
+		if (buf[n] & 0x80)
+			return(-1);
+	}
+	return(0);
+}