A web shell is a malicious script uploaded to a server to provide persistent, remote access for an attacker. To prevent this backdoor from being exploited again by the original attacker or others, the primary remediation step is to remove the web shell file and any other persistence mechanisms it may have established. This action is part of the "Eradication" phase of the incident response lifecycle, which focuses on eliminating the components of the incident to prevent future unauthorized access through the same vector.

B. Spin down the infrastructure.

This is an extreme containment measure that impacts availability. It is not a targeted solution for removing a specific malicious file and is typically reserved for widespread or uncontained incidents.

C. Preserve artifacts.

This is a critical step for forensic investigation to understand the attack's scope and origin. However, preserving evidence does not, by itself, prevent the web shell from being actively exploited.

D. Perform secure data destruction.

This is an end-of-lifecycle process for permanently deleting data from storage media. It is not a standard remediation technique for a malware infection on a production system.

1. National Institute of Standards and Technology (NIST). (2012). Computer Security Incident Handling Guide (Special Publication 800-61 Rev. 2).

Section 3.3.2

Eradication: This section details the process of removing malicious components from the system. It states

"After an incident has been contained

eradication may be necessary to eliminate components of the incident

such as deleting malware and disabling breached user accounts..." A web shell is a form of malware

and removing it is a direct act of eradication.

2. The Open Web Application Security Project (OWASP). (n.d.). Web Shells. OWASP Foundation.

Remediation Section: While not explicitly titled

the document's context on detection and prevention implies that the primary remediation is removal. It describes web shells as providing "a backdoor to a victim’s web server

" reinforcing that removing this backdoor (a persistence mechanism) is the necessary action to prevent further exploitation.

3. Mitre. (2023). ATT&CK T1505.003 - Server Software Component: Web Shell. MITRE ATT&CK Framework.

Mitigation M1050

Exploit Protection: The framework suggests hardening servers to prevent initial exploitation. In the context of post-exploitation

the implied mitigation is the removal of the malicious component. The description of a web shell as a means of "persistent access" directly links it to being a persistence mechanism that must be removed.