From bfdc509243f65c49920a700a6ea958f2291841c2 Mon Sep 17 00:00:00 2001
From: Thomas Stromberg <t+github@chainguard.dev>
Date: Tue, 19 Sep 2023 17:18:35 -0400
Subject: [PATCH] new check: hidden cwd events

---
 detection/evasion/hidden-cwd-events-linux.sql | 76 +++++++++++++++++++
 1 file changed, 76 insertions(+)
 create mode 100644 detection/evasion/hidden-cwd-events-linux.sql

diff --git a/detection/evasion/hidden-cwd-events-linux.sql b/detection/evasion/hidden-cwd-events-linux.sql
new file mode 100644
index 0000000..1d1a902
--- /dev/null
+++ b/detection/evasion/hidden-cwd-events-linux.sql
@@ -0,0 +1,76 @@
+-- Programs running with a hidden current working directory (event-based)
+--
+-- false positives:
+--   * Users rummaging through their configuration files
+--
+-- NOTES:
+--   * Disabled on macOS, as the cwd field as NULL there
+--
+-- references:
+--   * https://attack.mitre.org/techniques/T1564/001/ (Hide Artifacts: Hidden Files and Directories)
+--
+-- tags: transient
+-- platform: linux
+-- interval: 600
+SELECT
+    COALESCE(REGEX_MATCH(TRIM(pe.cwd, '"'), "/(\..*?)\/", 1), REGEX_MATCH(TRIM(pe.cwd, '"'), "/(\..*)", 1)) AS hidden_base,
+    REGEX_MATCH(TRIM(pe.cwd, '"'), "/(\..*)", 1) AS hidden_part,
+    COALESCE(REGEX_MATCH (TRIM(pe.cwd, '"'), '.*/(.*)', 1), pe.cwd) AS basename,
+    CONCAT (
+        COALESCE(REGEX_MATCH (TRIM(pe.path, '"'), '.*/(.*)', 1), pe.path),
+        ',',
+        REGEX_MATCH(TRIM(pe.cwd, '"'), "/(\..*?)\/", 1), REGEX_MATCH(TRIM(pe.cwd, '"'), "/(\..*)", 1)
+    ) AS exception_key,
+    -- Child
+    pe.path AS p0_path,
+    COALESCE(REGEX_MATCH (pe.path, '.*/(.*)', 1), pe.path) AS p0_name,
+    TRIM(pe.cmdline) AS p0_cmd,
+    TRIM(pe.cwd, '"') AS p0_cwd,
+    pe.status AS p0_status,
+    pe.time AS p0_time,
+    pe.pid AS p0_pid,
+    pe.euid AS p0_euid,
+    -- Parent
+    pe.parent AS p1_pid,
+    TRIM(COALESCE(p1.cmdline, pe1.cmdline)) AS p1_cmd,
+    p1.cwd AS p1_cwd,
+    COALESCE(p1.path, pe1.path) AS p1_path,
+    COALESCE(p_hash1.sha256, pe_hash1.sha256) AS p1_hash,
+    REGEX_MATCH (COALESCE(p1.path, pe1.path), '.*/(.*)', 1) AS p1_name
+FROM
+    process_events pe
+    LEFT JOIN users u ON pe.uid = u.uid
+    LEFT JOIN processes p ON pe.pid = p.pid -- Parents (via two paths)
+    LEFT JOIN processes p1 ON pe.parent = p1.pid
+    LEFT JOIN hash p_hash1 ON p1.path = p_hash1.path
+    LEFT JOIN process_events pe1 ON pe.parent = pe1.pid
+    AND pe1.time > (strftime('%s', 'now') -60660)
+    AND pe1.cmdline != ''
+    LEFT JOIN hash pe_hash1 ON pe1.path = pe_hash1.path
+WHERE
+    pe.time > (strftime('%s', 'now') -60600)
+    AND pe.cwd LIKE '%/.%'
+    AND NOT (
+        hidden_base IN (
+            '.cache',
+            '.cargo',
+            '.gradle',
+            '.kotlin',
+            '.npm',
+            '.git',
+            '.gimme',
+            '.vscode',
+            '.vim',
+            '.config',
+            '.provisio',
+            '.terraform.d',
+            '.emacs.d',
+            '.gmailctl',
+            '.oh-my-zsh',
+            '.zsh'
+        )
+        OR exception_key LIKE '%sh,~/.Trash'
+    )
+GROUP BY
+    p.cmdline,
+    p.cwd;
\ No newline at end of file