  Here, we investigate the security of the practical one-way CVQKD and
CV-MDI-QKD systems under laser seeding attack. In particular, Eve can inject a
suitable light into the laser diodes of the light source modules in the two
kinds of practical CVQKD systems, which results in the increased intensity of
the generated optical signal. The parameter estimation under the attack shows
that the secret key rates of these two schemes may be overestimated, which
opens a security loophole for Eve to successfully perform an intercept-resend
attack on these systems. To close this loophole, we propose a real-time
monitoring scheme to precisely evaluate the secret key rates of these schemes.
The analysis results indicate the implementation of the proposed monitoring
scheme can effectively resist this potential attack.
