In recent years, frequent geopolitical conflicts and the potential formation of alliances based on shared values have undermined the efficiently functioning, tightly interdependent network of global value chains (GVCs). This study proposes a novel conceptual framework for assessing GVC vulnerability, develops composite metrics to quantify GVC vulnerability at the economy and sector levels, and systematically investigates how current geopolitical risks amplify GVC vulnerabilities across economies and sectors. The empirical results indicate that accounting for geopolitical risks leads to increases in the vulnerabilities of economies participating in GVCs, to varying degrees. The amplification effect is particularly pronounced for the United States and economies with high GVC dependency on the U.S. At the key sector level: in the computer, electronic, and optical equipment manufacturing sector, major supply-hub countries in the value chain such as the U.S., Germany, and the U.K. exhibit relatively low vulnerability; in the basic pharmaceutical products and drug formulations manufacturing sector, China has the lowest vulnerability globally, though it is more sensitive to geopolitical risks. A scenario simulation analysis of the U.S.-Japan-India-Australia Quadrilateral Security Dialogue (Quad) alliance indicates that eliminating geopolitical risks among member states has a very limited effect on enhancing the security of their participation in GVCs. If the Quad further escalates into consistent geopolitical tensions with China, it will instead exacerbate the GVC vulnerability of the U.S., Japan, and Australia.