falco: add rules for git hook tampering and unexpected pack-service children

Written after the 2026-08-10/11 gitea internal-API log-poisoning attack
that planted a malicious uploadpack.packObjectsHook backdoor. Catches
both the planting (unexpected exec from a hooks/ path) and the firing
(git-upload-pack/git-receive-pack spawning anything but its own
pack-objects binary), independent of how the hook config got written.

falco/rules/git-hook-tamper.yaml

@@ -0,0 +1,29 @@
+# Custom rule: catch execution of any git hook file gitea didn't put there.
+# Added after the 2026-08-10/11 gitea internal-API log-poisoning attack, where
+# an attacker used /api/internal/manager/add-logger to write a malicious
+# uploadpack.packObjectsHook entry into the global .gitconfig, pointed at a
+# planted hooks/pre-applypatch.sample file under an unrelated repo. Gitea only
+# ever manages four hook names per repo (post-receive, pre-receive, update,
+# proc-receive), each delegating to a same-named script under hooks/*.d/gitea -
+# anything else executing from a hooks/ path is not something Gitea put there.
+
+- list: gitea_managed_hook_names
+  items: [post-receive, pre-receive, update, proc-receive, gitea]
+
+- rule: Unexpected git hook execution
+  desc: >
+    A process executed from a path under a git repository's hooks/ directory
+    whose name isn't one of Gitea's own managed hook scripts. Catches planted
+    hooks used for persistence/RCE (e.g. a malicious uploadpack.packObjectsHook
+    or receive hook), independent of how the file got written.
+  condition: >
+    spawned_process
+    and container.name = "gitea"
+    and proc.exepath contains "/hooks/"
+    and not proc.name in (gitea_managed_hook_names)
+  output: >
+    Unexpected git hook executed
+    (user=%user.name command=%proc.cmdline exepath=%proc.exepath
+    parent=%proc.pname container=%container.name pid=%proc.pid)
+  priority: CRITICAL
+  tags: [git, persistence, mitre_persistence]