cyberstrikeus T1552.004 Private Keys
Sub-technique of: T1552
High-Level Description
Adversaries may search for private key certificate files on compromised systems for insecurely stored credentials. Private cryptographic keys and certificates are used for authentication, encryption/decryption, and digital signatures. Common key and certificate file extensions include: .key, .pgp, .gpg, .ppk., .p12, .pem, .pfx, .cer, .p7b, .asc.
Adversaries may also look in common key directories, such as ~/.ssh for SSH keys on * nix-based systems or C:\Users\(username)\.ssh\ on Windows. Adversary tools may also search compromised systems for file extensions relating to cryptographic keys and certificates.
When a device is registered to Entra ID, a device key and a transport key are generated and used to verify the device’s identity. An adversary with access to the device may be able to export the keys in order to impersonate the device.
On network devices, private keys may be exported via Network Device CLI commands such as crypto pki export.
Some private keys require a password or passphrase for operation, so an adversary may also use Input Capture for keylogging or attempt to Brute Force the passphrase off-line. These private keys can be used to authenticate to Remote Services like SSH or for use in decrypting other collected files such as email.
Kill Chain Phase
- Credential Access (TA0006)
Platforms: Linux, macOS, Network Devices, Windows
What to Check
- Identify if Private Keys technique is applicable to target environment
- Check Linux systems for indicators of Private Keys
- Check macOS systems for indicators of Private Keys
- Check Network Devices systems for indicators of Private Keys
- Verify mitigations are bypassed or absent (4 known mitigations)
- Assess detection coverage (1 detection strategies)
How to Test
Atomic Red Team Tests
The following tests are from Atomic Red Team and provide actionable ways to test this technique:
Atomic Test 1: Private Keys
Find private keys on the Windows file system. File extensions include: .key, .pgp, .gpg, .ppk., .p12, .pem, pfx, .cer, .p7b, .asc
Supported Platforms: windows Elevation Required: Yes
dir c:\ /b /s .key | findstr /e .key
Atomic Test 2: Discover Private SSH Keys
Discover private SSH keys on a FreeBSD, macOS or Linux system.
Supported Platforms: linux, macos
find #{search_path} -name id_rsa 2>/dev/null >> #{output_file}
exit 0
Atomic Test 3: Copy Private SSH Keys with CP
Copy private SSH keys on a Linux system to a staging folder using the cp command.
Supported Platforms: linux
mkdir #{output_folder}
find #{search_path} -name id_rsa 2>/dev/null -exec cp --parents {} #{output_folder} \;
exit 0
Atomic Test 4: Copy Private SSH Keys with CP (freebsd)
Copy private SSH keys on a FreeBSD system to a staging folder using the cp command.
Supported Platforms: linux
mkdir #{output_folder}
find #{search_path} -name id_rsa 2>/dev/null -exec gcp --parents {} #{output_folder} \;
Dependencies:
- Install GNU cp from coreutils package.
Atomic Test 5: Copy Private SSH Keys with rsync
Copy private SSH keys on a Linux or macOS system to a staging folder using the rsync command.
Supported Platforms: macos, linux
mkdir #{output_folder}
find #{search_path} -name id_rsa 2>/dev/null -exec rsync -R {} #{output_folder} \;
exit 0
Manual Testing
If Atomic Red Team tests are not applicable, manually verify the technique by:
Identify Attack Surface: Determine if the target environment is susceptible to Private Keys by examining the target platforms (Linux, macOS, Network Devices).
Assess Existing Defenses: Review whether mitigations for T1552.004 are in place. If defenses are absent or misconfigured, this technique may be exploitable.
Execute Test: Use tools and methods described in the MITRE ATT&CK page and external references below.
Remediation Guide
M1027 Password Policies
Use strong passphrases for private keys to make cracking difficult.
M1022 Restrict File and Directory Permissions
Ensure permissions are properly set on folders containing sensitive private keys to prevent unintended access. Additionally, on Cisco devices, set the nonexportable flag during RSA key pair generation.
M1047 Audit
Ensure only authorized keys are allowed access to critical resources and audit access lists regularly.
M1041 Encrypt Sensitive Information
When possible, store keys on separate cryptographic hardware instead of on the local system. For example, on Windows systems use a TPM to secure keys and other sensitive credential material.
Detection
Detect Suspicious Access to Private Key Files and Export Attempts Across Platforms
Risk Assessment
| Finding | Severity | Impact |
|---|---|---|
| Private Keys technique applicable | High | Credential Access |
CWE Categories
| CWE ID | Title |
|---|---|
| CWE-522 | Insufficiently Protected Credentials |