Log analysis device, log analysis method, and log analysis program

1. A log analysis device comprising:

a memory; and a processor coupled to the memory and programmed to execute a process comprising:

acquiring a communication log to be analyzed obtained from communications in a predetermined network;

detecting a terminal conforming to an analysis rule using a signature generated based on a characteristic of a communication log generated by a terminal infected with malware;

calculating a score indicating a degree of threat for a detection result including information on the terminal detected by the detecting and an analysis rule to which the terminal conforms using information on the analysis rule and information on the detection result; and

outputting the detection result and the score calculated by the calculating,

wherein the calculating includes calculating a continuity score indicating continuity of the detection result by making the continuity score larger as date and time when the detection is performed for a first time is in more distant past and as a number of times the detection is performed in a predetermined period of time is larger.

2. The log analysis device according to claim 1 , wherein

the detecting detects a terminal having number of times a pair of a predetermined field and a value included in the communication log to be analyzed matches the signature of equal to or larger than a threshold set in advance, and

the calculating calculates the score based on the degree of threat of the signature set in advance and a degree of deviation of the number of times from the threshold.

3. The log analysis device according to claim 1 , wherein the calculating calculates the score based on a period of time and a frequency of occurrence of a detection result including information on the same terminal and the same analysis rule as the information on the terminal and the analysis rule included in the detection result.

4. The log analysis device according to claim 1 , wherein

the detecting detects a terminal having number of times a pair of a predetermined field and a value included in the communication log to be analyzed matches the signature of equal to or larger than a threshold set in advance,

the calculating calculates a first score based on the degree of threat of the signature set in advance and a degree of deviation of the number of times from the threshold and calculates a second score based on a period of time and a frequency of occurrence of a detection result including information on the same terminal and the same analysis rule as the information on the terminal and the analysis rule included in the detection result and on the first score, and

the outputting outputs at least the information on the terminal included in the detection result and the second score.

5. The log analysis device according to claim 1 , wherein the process further comprising:

excluding a first detection result satisfying a predetermined condition out of a plurality of the detection results obtained by the detecting, wherein

the calculating calculates the score for a second detection result other than the first detection result excluded by the excluding out of the detection results obtained by the detecting.

6. The log analysis device according to claim 5 , wherein the process further comprising:

receiving selection indicating whether the detection result need not be dealt with, wherein

the excluding excludes the detection result in at least one of a case where a frequency of occurrence in the network of a communication log having the same characteristic as a characteristic of the signature used by the analysis rule included in the detection result is equal to or higher than a predetermined value and a case where the determination that the detection result need not be dealt with is received in advance by the receiving.

7. A log analysis method performed by a log analysis device, the log analysis method comprising:

acquiring a communication log to be analyzed obtained from communications in a predetermined network;

detecting a terminal conforming to an analysis rule using a signature generated based on a characteristic of a communication log generated by a terminal infected with malware;

calculating a score indicating a degree of threat for a detection result including information on the terminal detected at the detecting and an analysis rule to which the terminal conforms using information on the analysis rule and information on the detection result; and

outputting the detection result and the score calculated at the calculating,

wherein the calculating includes calculating a continuity score indicating continuity of the detection result by making the continuity score larger as date and time when the detection is performed for a first time is in more distant past and as a number of times the detection is performed in a predetermined period of time is larger.

8. A non-transitory computer-readable recording medium having stored a program for log analysis program that causes a computer to execute a process comprising:

acquiring a communication log to be analyzed obtained from communications in a predetermined network;

detecting a terminal conforming to an analysis rule using a signature generated based on a characteristic of a communication log generated by a terminal infected with malware;

calculating a score indicating a degree of threat for a detection result including information on the terminal detected by the detecting and an analysis rule to which the terminal conforms using information on the analysis rule and information on the detection result; and

outputting the detection result and the score calculated by the calculating,

wherein the calculating includes calculating a continuity score indicating continuity of the detection result by making the continuity score larger as date and time when the detection is performed for a first time is in more distant past and as a number of times the detection is performed in a predetermined period of time is larger.