Techniques for ransomware detection and mitigation
An attacker who gains control of a computer system using malicious software (malware) may be able to do anything to the data on the system. One type of malware, sometimes referred to as ransomware, can encrypt the contents of a hard drive or other data repository, preventing those contents from being accessed by their rightful owners. A ransomware attack can be greatly disruptive to an individual or business, and result in loss of data and loss of computer system uptime, impacting overall computing productivity. By detecting that ransomware is operating on a computer (e.g. by correlating between the original data and content in different cache layers), the negative effects of the ransomware may be mitigated or avoided.
1. A non-transitory machine-readable medium having stored thereon machine-readable instructions which, when executed by one or more processors, cause a machine to perform operations comprising:
detecting that a cache of a computer system includes a first copy of original content loaded from a file;
retaining, in the cache, a second copy of the original content loaded from the file;
determining, via an analysis of modified content detected in the first copy, that the modified content represents an attempted change to the original content of the file;
comparing the original content of the second copy to the modified content detected in the first copy to determine if the modified content represents an encrypted version of the original content; and
preventing the original content from being deleted if the modified content has been encrypted.
2. The non-transitory machine-readable medium of claim 1 , wherein the comparing includes determining if a first entropy level for the modified content is higher than a second entropy level for the original content.
3. The non-transitory machine-readable medium of claim 2 , wherein determining if the first entropy level is higher comprises determining if a threshold amount of increase in overall entropy has occurred.
4. The non-transitory machine readable medium of claim 1 , wherein the operations further comprise:
detecting that the cache has received particular data to be written to long-term storage; and
correlating the particular data to the original content;
wherein the comparing is performed based on the correlating.
5. The non-transitory machine-readable medium of claim 1 , wherein the cache is a user-level software-implemented cache.
6. The non-transitory machine-readable medium of claim 1 , wherein the cache is a system-level software-implemented cache.
7. The non-transitory machine-readable medium of claim 1 , wherein the operations further comprise checking a plurality of software-implemented caches to determine if the original content of the file has been changed.
8. The non-transitory machine-readable medium of claim 1 , wherein the analysis of the modified content includes analyzing an entirety of the file and an entirety of a modified version of the file.
9. The non-transitory machine-readable medium of claim 1 , wherein the operations further comprise:
prior to the preventing, checking if a program that produced the modified content is on a whitelist of allowable programs; and
if the program is on the whitelist, allowing the original content to be deleted rather than preventing its deletion.
10. A method, comprising:
detecting that a first copy of original content of a file has been loaded into a cache of a computer system;
retaining, in the cache of the computer system, a second copy of the original content of the file;
determining that the first copy of original content of the file has been changed to produce altered content;
comparing the original content from the second copy to the altered content to determine if the altered content represents an encrypted version of the original content; and
preventing the original content from being deleted if the altered content has been encrypted.
11. The method of claim 10 , wherein the preventing comprises causing an alert to be electronically transmitted to a user of the computer system, wherein the alert allows the user to override a data deletion operation.
12. The method of claim 10 , wherein the preventing comprises causing a backup copy of the original content to be sent to a remote server.
13. The method of claim 10 , wherein the detecting is performed by a software process running on the computer system.
14. The method of claim 10 , wherein the detecting is performed by a hardware device attached to the computer system, and wherein the cache is a hardware-implemented cache.
15. The method of claim 10 , wherein the preventing comprises automatically halting execution, on the computer system, of a process that is attempting to delete the original content of the file.
16. A system, comprising:
a primary memory;
a secondary memory; and
one or more hardware processors coupled to the primary memory and the secondary memory, wherein the one or more processors are configured to execute instructions to cause the system to perform operations comprising:
detecting that a cache of the system includes a first copy of a file read from a permanent storage device;
retaining, in the cache, a second copy of the file read from the permanent storage device;
determining, via an analysis of modified content detected in the cache, that the modified content represents an attempted change to the contents of the file by a particular process executing on the system;
comparing, using the second copy of the file read from the permanent storage device, original content of the file to the modified content in the cache to determine if the modified content represents an encrypted version of the original content; and
preventing the particular process from deleting the original content of the file from the permanent storage if the modified content has been encrypted and does not correspond to a program on a whitelist.
17. The system of claim 16 , wherein the operations further comprise capturing an encryption key used by the particular process executing on the system and transmitting the captured encryption key.
18. The system of claim 16 , wherein the whitelist includes one or more programs authorized by a system administrator that perform at least one of encryption or compression.
19. The system of claim 16 , further comprising a hardware cache corresponding to the primary memory;
wherein determining that contents of the file have been changed includes an analysis of contents of the hardware cache.
20. The system of claim 16 , wherein the analysis of the modified content includes analyzing a limited portion of the file and a corresponding limited portion of a modified version of the file.