From af4c44d8c8e5c576f92b74fe64f604a33d0a5aa9 Mon Sep 17 00:00:00 2001
From: "google-labs-jules[bot]"
 <161369871+google-labs-jules[bot]@users.noreply.github.com>
Date: Fri, 10 Apr 2026 05:06:03 +0000
Subject: [PATCH] =?UTF-8?q?=F0=9F=9B=A1=EF=B8=8F=20Sentinel:=20[CRITICAL]?=
 =?UTF-8?q?=20Fix=20TOCTOU=20vulnerability=20in=20SSH=20key=20generation?=
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Wrapped the private key extraction in a subshell `(umask 077 && ...)` so the file is inherently created with 0600 permissions, avoiding the TOCTOU issue completely.
Also updated `.jules/sentinel.md` with the new learning.

Co-authored-by: kidchenko <5432753+kidchenko@users.noreply.github.com>
---
 .jules/sentinel.md      | 5 +++++
 tools/setup-ssh-keys.sh | 2 +-
 2 files changed, 6 insertions(+), 1 deletion(-)
 create mode 100644 .jules/sentinel.md

diff --git a/.jules/sentinel.md b/.jules/sentinel.md
new file mode 100644
index 0000000..fd1d85f
--- /dev/null
+++ b/.jules/sentinel.md
@@ -0,0 +1,5 @@
+## 2026-04-10 - [TOCTOU vulnerability in SSH key generation]
+
+**Vulnerability:** Private SSH keys written to disk using shell redirection (`> "$PRIVATE_KEY_FILE"`) followed by `chmod 600`.
+**Learning:** Shell redirection creates the file according to the system's `umask`. If the `umask` allows, the file might briefly be readable by other users before `chmod 600` executes, causing a Time-of-Check to Time-of-Use (TOCTOU) vulnerability.
+**Prevention:** Wrap file creation steps that handle sensitive data in a subshell using `(umask 077 && command > file)` so that the file is created with secure permissions right from the start.
diff --git a/tools/setup-ssh-keys.sh b/tools/setup-ssh-keys.sh
index bde52fd..6ecd8db 100755
--- a/tools/setup-ssh-keys.sh
+++ b/tools/setup-ssh-keys.sh
@@ -153,7 +153,7 @@ cmd_restore() {
     chmod 700 "$SSH_DIR"
 
     # Read private key from 1Password and save locally
-    op read "op://$VAULT/$KEY_NAME/private_key" > "$PRIVATE_KEY_FILE"
+    (umask 077 && op read "op://$VAULT/$KEY_NAME/private_key" > "$PRIVATE_KEY_FILE")
     chmod 600 "$PRIVATE_KEY_FILE"
 
     # Read public key from 1Password and save locally