The development of high harmonic generation (HHG) over the past three decades has resulted in accessible table-top coherent XUV sources with subfemtosecond pulse durations . The extremely short time resolution of these attosecond light sources not only permits direct timedomain measurements of electronic dynamics in atomic , molecular , and solidstate systems , but also provides the foundation for tabletop versions of XUV nonlinear spectroscopy. A recently developed extension of these techniques , attosecond XUV fourwave mixing (FWM) spectroscopy, utilizes a short attosecond XUV pulse train produced by HHG and two noncollinear near-infrared (NIR) pulses to generate spatially-isolated third order polarization signals. These transient emission signals encode the evolution of excited states and represent background-free measurements of XUV-induced chemical dynamics . This technique has already been applied to monitor electronic and vibronic coherences in multiple atomic and diatomic systems , facilitating the characterization of a previously inaccessible dark state in N2 , the detection of light-induced states in He , and the implementation of a variant of XUV multidimensional spectroscopy in long-lived Rydberg states of Ar . Moreover, attosecond wave-mixing experiments have revealed order-dependent emission delays in nonlinear signal generation and measured ultrafast dynamics due to autoionization and Auger decay in atomic , diatomic , and solid-state systems . Here, we extend attosecond XUV FWM spectroscopy to probe autoionization dynamics in a polyatomic system, the inner valence Rydberg states of carbon dioxide.