diff --git a/docs/CHANGES.TXT b/docs/CHANGES.TXT
index 19eb08ddb..f96dd2ea5 100644
--- a/docs/CHANGES.TXT
+++ b/docs/CHANGES.TXT
@@ -6,6 +6,7 @@
 - Fix: 32-bit build failures on i686 and armv7l architectures
 - Fix: Legacy command-line argument compatibility (-1, -2, -12, --sc, --svc)
 - Fix: Prevent heap buffer overflow in Teletext processing (security fix)
+- Fix: Prevent integer overflow leading to heap buffer overflow in Transport Stream handling (security fix)
 - Fix: Lazy OCR initialization - only initialize when first DVB subtitle is encountered
 - Build: Optimized Windows CI workflow for faster builds
 - Fix: Updated GUI with version 0.7.1. A blind attempt to fix a hang on start on some Windows.
diff --git a/src/lib_ccx/ccx_decoders_608.c b/src/lib_ccx/ccx_decoders_608.c
index 37a057e83..c2b0a0aea 100644
--- a/src/lib_ccx/ccx_decoders_608.c
+++ b/src/lib_ccx/ccx_decoders_608.c
@@ -316,10 +316,20 @@ int write_cc_buffer(ccx_decoder_608_context *context, struct cc_subtitle *sub)
 
 	if (!data->empty && context->output_format != CCX_OF_NULL)
 	{
-		struct eia608_screen *new_data = (struct eia608_screen *)realloc(sub->data, (sub->nb_data + 1) * sizeof(*data));
+		size_t new_size;
+
+		if (sub->nb_data + 1 > SIZE_MAX / sizeof(struct eia608_screen))
+		{
+			ccx_common_logging.log_ftn("Too many screens, cannot allocate more memory.\n");
+			return 0;
+		}
+
+		new_size = (sub->nb_data + 1) * sizeof(struct eia608_screen);
+
+		struct eia608_screen *new_data = (struct eia608_screen *)realloc(sub->data, new_size);
 		if (!new_data)
 		{
-			ccx_common_logging.log_ftn("No Memory left");
+			ccx_common_logging.log_ftn("Out of memory while reallocating screen buffer\n");
 			return 0;
 		}
 		sub->data = new_data;
@@ -386,10 +396,20 @@ int write_cc_line(ccx_decoder_608_context *context, struct cc_subtitle *sub)
 
 	if (!data->empty)
 	{
-		struct eia608_screen *new_data = (struct eia608_screen *)realloc(sub->data, (sub->nb_data + 1) * sizeof(*data));
+		size_t new_size;
+
+		if (sub->nb_data + 1 > SIZE_MAX / sizeof(struct eia608_screen))
+		{
+			ccx_common_logging.log_ftn("Too many screens, cannot allocate more memory.\n");
+			return 0;
+		}
+
+		new_size = (sub->nb_data + 1) * sizeof(struct eia608_screen);
+
+		struct eia608_screen *new_data = (struct eia608_screen *)realloc(sub->data, new_size);
 		if (!new_data)
 		{
-			ccx_common_logging.log_ftn("No Memory left");
+			ccx_common_logging.log_ftn("Out of memory while reallocating screen buffer\n");
 			return 0;
 		}
 		sub->data = new_data;
diff --git a/src/lib_ccx/ccx_decoders_isdb.c b/src/lib_ccx/ccx_decoders_isdb.c
index 5a1f5f588..5a54340df 100644
--- a/src/lib_ccx/ccx_decoders_isdb.c
+++ b/src/lib_ccx/ccx_decoders_isdb.c
@@ -724,16 +724,17 @@ static int parse_csi(ISDBSubContext *ctx, const uint8_t *buf, int len)
 	// Copy buf in arg
 	for (i = 0; *buf != 0x20; i++)
 	{
-		if (i >= (sizeof(arg)) + 1)
+		if (i >= sizeof(arg) - 1)
 		{
-			isdb_log("UnExpected CSI %d >= %d", sizeof(arg) + 1, i);
+			isdb_log("UnExpected CSI: too long");
 			break;
 		}
 		arg[i] = *buf;
 		buf++;
 	}
 	/* ignore terminating 0x20 character */
-	arg[i] = *buf++;
+	if (i < sizeof(arg))
+		arg[i] = *buf++;
 
 	switch (*buf)
 	{
diff --git a/src/lib_ccx/ts_functions.c b/src/lib_ccx/ts_functions.c
index 683c4fcf5..2f31b0f78 100644
--- a/src/lib_ccx/ts_functions.c
+++ b/src/lib_ccx/ts_functions.c
@@ -670,7 +670,6 @@ void cinfo_cremation(struct ccx_demuxer *ctx, struct demuxer_data **data)
 
 int copy_payload_to_capbuf(struct cap_info *cinfo, struct ts_payload *payload)
 {
-	int newcapbuflen;
 
 	if (cinfo->ignore == CCX_TRUE &&
 	    ((cinfo->stream != CCX_STREAM_TYPE_VIDEO_MPEG2 &&
@@ -696,17 +695,22 @@ int copy_payload_to_capbuf(struct cap_info *cinfo, struct ts_payload *payload)
 	}
 
 	// copy payload to capbuf
-	newcapbuflen = cinfo->capbuflen + payload->length;
-	if (newcapbuflen > cinfo->capbufsize)
+	if (payload->length > INT64_MAX - cinfo->capbuflen)
 	{
-		unsigned char *new_capbuf = (unsigned char *)realloc(cinfo->capbuf, newcapbuflen);
+		mprint("Error: capbuf size overflow\n");
+		return -1;
+	}
+	int64_t newcapbuflen = (int64_t)cinfo->capbuflen + payload->length;
+	if (newcapbuflen > (int64_t)cinfo->capbufsize)
+	{
+		unsigned char *new_capbuf = (unsigned char *)realloc(cinfo->capbuf, (size_t)newcapbuflen);
 		if (!new_capbuf)
 			return -1;
 		cinfo->capbuf = new_capbuf;
-		cinfo->capbufsize = newcapbuflen;
+		cinfo->capbufsize = newcapbuflen; // Note: capbufsize is int in struct cap_info
 	}
 	memcpy(cinfo->capbuf + cinfo->capbuflen, payload->start, payload->length);
-	cinfo->capbuflen = newcapbuflen;
+	cinfo->capbuflen = newcapbuflen; // Note: capbuflen is int in struct cap_info
 
 	return CCX_OK;
 }