/etc/passwd and /etc/shadow

Executive Summary

/etc/passwd and /etc/shadow (T1003.008) is a MITRE ATT&CK technique associated with Credential Access. Adversaries may attempt to dump the contents of <code>/etc/passwd</code> and <code>/etc/shadow</code> to enable offline password cracking.

Why Attackers Use It

Attackers use /etc/passwd and /etc/shadow because it provides a reliable way to advance their objective within the Credential Access tactic, often with a favorable balance of impact versus detectability on Linux environments. Defenders should assess this behavior in the context of the affected platform and adjacent activity rather than treating it as a standalone indicator.

MITRE Description

Adversaries may attempt to dump the contents of <code>/etc/passwd</code> and <code>/etc/shadow</code> to enable offline password cracking. Most modern Linux operating systems use a combination of <code>/etc/passwd</code> and <code>/etc/shadow</code> to store user account information, including password hashes in <code>/etc/shadow</code>. By default, <code>/etc/shadow</code> is only readable by the root user.(Citation: Linux Password and Shadow File Formats)

Linux stores user information such as user ID, group ID, home directory path, and login shell in <code>/etc/passwd</code>. A "user" on the system may belong to a person or a service. All password hashes are stored in <code>/etc/shadow</code> - including entries for users with no passwords and users with locked or disabled accounts.(Citation: Linux Password and Shadow File Formats)

Adversaries may attempt to read or dump the <code>/etc/passwd</code> and <code>/etc/shadow</code> files on Linux systems via command line utilities such as the <code>cat</code> command.(Citation: Arctic Wolf) Additionally, the Linux utility <code>unshadow</code> can be used to combine the two files in a format suited for password cracking utilities such as John the Ripper - for example, via the command <code>/usr/bin/unshadow /etc/passwd /etc/shadow > /tmp/crack.password.db</code>(Citation: nixCraft - John the Ripper). Since the user information stored in <code>/etc/passwd</code> are linked to the password hashes in <code>/etc/shadow</code>, an adversary would need to have access to both.

Attack Flow

1. Attacker gains the prerequisite access or context described below.
2. Attacker executes /etc/passwd and /etc/shadow to achieve its tactical objective (Credential Access).
3. Resulting access/data/effect is leveraged to advance the broader attack chain (see Related Techniques).

Prerequisites

• Platform(s): Linux
• ATT&CK does not define one universal permission requirement for this technique. Establish the required access from the observed implementation and affected platform.

Common Tools

• Tool attribution is implementation-specific. Use ATT&CK procedure examples and local telemetry to identify the binaries, services, scripts, accounts, or cloud resources involved.

Commands

No universal command represents /etc/passwd and /etc/shadow. Capture the exact command line, arguments, parent process, account, host, and execution time from the investigated environment; do not operationalize unverified examples.

Network Traffic

• Network observability is implementation-dependent. Review DNS, proxy, firewall, flow, authentication, and packet telemetry around the activity window, then correlate remote endpoints and protocol behavior with host evidence.

Windows Events

Sysmon Events

Detection Opportunities

No MITRE detection guidance published for this technique.

Relevant ATT&CK Data Sources: N/A

Sigma Rules

A universal Sigma rule would create unreliable results because this technique has no single guaranteed observable. Build detection logic from a documented behavior and supported data source, scope it to the affected platform, and validate it against benign administrative activity before deployment.

Splunk Queries

Start with the data sources named in the detection section. Scope searches by asset, identity, and time window; correlate the primary behavior with preceding access and subsequent actions. A portable query is intentionally not provided where the technique lacks a universal schema or observable.

Investigation Workflow

1. Confirm that the observed behavior is consistent with /etc/passwd and /etc/shadow and rule out expected administrative or application activity.
2. Establish the first-seen time, initiating identity, source system, target system, and affected resources.
3. Collect relevant host, identity, network, cloud, and application telemetry for the surrounding time window.
4. Correlate parent and child activity, remote connections, file or configuration changes, and related ATT&CK techniques.
5. Determine scope by searching for the same observable across peer assets and identities.
6. Preserve volatile evidence and record confidence, assumptions, and telemetry gaps before containment.

Containment

1. Isolate affected host(s)/account(s) identified during investigation.
2. Revoke or rotate any credentials/tokens potentially exposed.
3. Apply the mitigations listed below where not already enforced.
4. Validate no related techniques (see Related Techniques) were chained against the same asset.

Mitigation

• M1026 -- Privileged Account Management: Privileged Account Management focuses on implementing policies, controls, and tools to securely manage privileged accounts (e.g., SYSTEM, root, or administrative accounts).
• M1027 -- Password Policies: Set and enforce secure password policies for accounts to reduce the likelihood of unauthorized access.

Related Techniques

• T1003