Netflix shares will march higher throughout 2018 as the company funnels cash into original content and subscribers upgrade to 4K ultra-high-definition televisions, according to two Wall Street firms.

UBS told clients Monday that it revised its financial estimates for Netflix upward as the company's efforts in original content and customer retention widen its competitive moat.

"Increasingly building out its global production muscle and focusing on content that travels internationally, Netflix has emerged as a content powerhouse that is actively building a global moat," wrote UBS analyst Eric Sheridan on Monday. "We see ample runway ahead for

international subscriber growth given: low penetration of existing global broadband households [and] low broadband penetration in international markets."

Sheridan added that Netflix has achieved the same level of interest and recognition that premium programming producers generate. The second season of Netflix's "Stranger Things," for instance, garnered higher search interest than every season of HBO's "Game of Thrones" in the U.S., according to the analyst.

"The international success of Netflix's original content also helps lower the incremental cost of acquiring and servicing new subscribers in domestic and foreign markets alike," Sheridan added, bumping his price target on Netflix to $345 from $290, implying 15 percent upside from Friday's close.