In a recent paper[J.Korean.Phys.Soc.49 (2006) 459],two GHZ-state-based quantum secure direct communi-cation protocols were presented.Here we point out that an eavesdropper can utilize a special property of GHZ states,i.e."correlation-elicitable" to obtain half information of the transmitted secrets without being detected in both protocols.The particular attack strategy is demonstrated in detail.Furthermore,a possible improvement is proposed,which makes the protocols secure against this kind of attack.