Malicious Browser Master Key Decryption Artifacts Written by Katz Stealer (via file_event)

ATT&CK techniques

Cred Access

Recon
Resource Dev
Initial Access
Execution
Persistence
Priv Esc
Defense Evasion
Cred Access
- T1555.003Credentials from Web Browsers
Discovery
Lateral Movement
Collection
C2
Exfiltration
Impact

What it detects

This rule detects creation of the decrypted browser master-key text files written by Katz Stealer after it extracts and decrypts Chrome, Edge, and Brave application-bound encryption keys. Adversaries leverage these staged key files to decrypt saved credentials and cookies offline, making detection valuable for catching browser credential theft in progress.

Reporting behind it

Related detections9 linkedT1555.003 — drag to rearrange

Malicious Fake Fortinet Patch Infostealer Execution (via process_creation)

Suspicious BoryptGrab Infostealer Staging Directory (via file_event)

Malicious Interlock Credential Stealer Output File

Suspicious AppleScript Payload Execution via osascript (macOS)

Suspicious RisePro Stealer Password Dump File in Temp (via file_event)

Malicious User Browser Credentials Dump via Network Share - DonPapi, Lazagne (via security)

Suspicious RegAsm MSBuild or AutoIt Accessing Browser Credential Stores

Suspicious Browser and Wallet Credential Theft via JavaScript Stealer

Malicious DPAPI Credential Decryption via PowerShell ProtectedData Unprotect

Malicious Browser Master Key Decryption Artifacts Written by Katz Stealer (via file_event)

Pivot detection · T1555.003 · 9 related

Detection content is published as a reviewed draft. Tune thresholds and exclusions against your own telemetry before enabling this rule for alerting.

Full detection rule

Unlock this rule to view and copy it

The detection logic is included with a plan. Everything else — context, mappings and implementation details — stays free on this page.

Sign in for 3 free unlocks

Signing in gives you 3 unlocks to spend on any rule in the library. No card, and they do not expire.

Also included

Unlocked rules convert on this page — to Splunk SPL or Splunk — Raw Index SPL or Microsoft Sentinel KQL or Microsoft Sentinel ASIM ASIM KQL or Microsoft Defender XDR KQL or Elastic Security KQL or Elastic Security Lucene or Elastic Security ES|QL or CrowdStrike Falcon CQL or SentinelOne PowerQuery or Palo Alto Cortex XDR XQL or Carbon Black Cloud Platform Search or Carbon Black EDR Process Search or Google Security Operations UDM Search or IBM QRadar AQL or Sumo Logic Cloud SIEM Rules expression or Rapid7 InsightIDR LEQL or Graylog Search or OpenSearch Lucene or OpenSearch PPL PPL or Grafana Loki LogQL or SQLite SQL or Zircolite SQLite — with the log-source profile the engine picked, the field map it used, and everything it could not express. Converting a rule you have unlocked costs no further credit.

See it run on a free rule →Convert your own rule →