WASHINGTON—Telecommunications gear made by China’s Huawei Technologies Co. is far more likely to contain flaws that could be leveraged by hackers for malicious use than equipment from rival companies, according to new research by cybersecurity experts that top U.S. officials said appeared credible.

Over half of the nearly 10,000 firmware images encoded into more than 500 variations of enterprise network-equipment devices tested by the researchers contained at least one such exploitable vulnerability, the researchers found....