  It is reported that the Large High Altitude Air Shower Observatory (LHAASO)
observed thousands of very-high-energy photons up to $\sim$18 TeV from GRB
221009A. We study the survival rate of these photons via considering the fact
that they are absorbed by the extragalactic background light. By performing a
set of $10^6$ Monte-Carlo simulations, we explore the parameter space allowed
by current observations and estimate the probability of predicting that LHAASO
detects at least one photon of 18 TeV from GRB 221009A. We find that the
standard physics is compatible with the observations of 18 TeV photons within
$3.5\sigma$ confidence interval. Our research method can be straightforwardly
generalized to study more data sets of LHAASO and other experiments in the
future.
