🛡️ Sentinel: Fix TOCTOU vulnerability in SSH key creation #21
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🚨 Severity: CRITICAL 💡 Vulnerability: SSH private keys were created with default permissions (often world-readable) before being restricted with `chmod`. This created a race condition (TOCTOU) where the key could be read by other users on the system. 🎯 Impact: Potential leakage of private SSH keys. 🔧 Fix: Used `umask 077` in a subshell during file creation to ensure keys are written with 600 permissions atomically. ✅ Verification: Verified syntax with `./build.sh` and manual code inspection. Co-authored-by: kidchenko <5432753+kidchenko@users.noreply.github.com>
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📝 WalkthroughWalkthroughA security-focused update adds documentation about TOCTOU race conditions in file creation and refactors a shell script to use subshells with explicit umask settings during file operations, enhancing permission handling consistency without changing functional outcomes. Changes
Estimated code review effort🎯 2 (Simple) | ⏱️ ~12 minutes Poem
🚥 Pre-merge checks | ✅ 3✅ Passed checks (3 passed)
✏️ Tip: You can configure your own custom pre-merge checks in the settings. ✨ Finishing touches
🧪 Generate unit tests (beta)
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Actionable comments posted: 1
🤖 Fix all issues with AI agents
In @.jules/sentinel.md:
- Around line 1-4: Change the document heading to an H1 and add blank lines
around it, and wrap long lines to satisfy MD041/MD022/MD013: replace the first
line "## 2024-05-22 - Secure File Creation in Shell Scripts" with "# 2024-05-22
- Secure File Creation in Shell Scripts", ensure there is a blank line before
and after that H1, and reflow the longer sentences in the body (e.g., the
"Vulnerability", "Learning", and "Prevention" lines) so each line is under the
project's max line length (commonly 80 chars) while preserving the content and
bullet/heading structure.
🧹 Nitpick comments (1)
tools/setup-ssh-keys.sh (1)
155-165: Consider atomic write to avoid empty key files onop readfailure.Redirection creates the target file before
op readexecutes; if the read fails, an empty key file is left behind. Use a temp file +mvto keep the write atomic while preserving the umask behavior.💡 Suggested change (atomic write)
- ( - umask 077 - op read "op://$VAULT/$KEY_NAME/private_key" > "$PRIVATE_KEY_FILE" - ) + ( + umask 077 + tmp_key="$(mktemp "${PRIVATE_KEY_FILE}.XXXXXX")" + op read "op://$VAULT/$KEY_NAME/private_key" > "$tmp_key" + mv -f "$tmp_key" "$PRIVATE_KEY_FILE" + ) @@ - ( - umask 022 - op read "op://$VAULT/$KEY_NAME/public_key" > "$PUBLIC_KEY_FILE" - ) + ( + umask 022 + tmp_pub="$(mktemp "${PUBLIC_KEY_FILE}.XXXXXX")" + op read "op://$VAULT/$KEY_NAME/public_key" > "$tmp_pub" + mv -f "$tmp_pub" "$PUBLIC_KEY_FILE" + )
| ## 2024-05-22 - Secure File Creation in Shell Scripts | ||
| **Vulnerability:** TOCTOU race condition when creating sensitive files (like SSH keys) using redirection (`>`) followed by `chmod`. | ||
| **Learning:** Files created via redirection inherit default permissions (usually 644/666) before `chmod` runs, leaving a window where they are world-readable. | ||
| **Prevention:** Use `umask` inside a subshell to strictly control permissions at creation time: `(umask 077; command > file)`. |
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Fix markdownlint violations (H1 + blank lines + wrap long lines).
The file fails MD041 (first line should be H1), MD022 (blank lines around heading), and MD013 (line length).
✅ Suggested fix
-## 2024-05-22 - Secure File Creation in Shell Scripts
-**Vulnerability:** TOCTOU race condition when creating sensitive files (like SSH keys) using redirection (`>`) followed by `chmod`.
-**Learning:** Files created via redirection inherit default permissions (usually 644/666) before `chmod` runs, leaving a window where they are world-readable.
-**Prevention:** Use `umask` inside a subshell to strictly control permissions at creation time: `(umask 077; command > file)`.
+# 2024-05-22 - Secure File Creation in Shell Scripts
+
+**Vulnerability:** TOCTOU race condition when creating sensitive files (like SSH keys)
+using redirection (`>`) followed by `chmod`.
+
+**Learning:** Files created via redirection inherit default permissions (usually
+644/666) before `chmod` runs, leaving a window where they are world-readable.
+
+**Prevention:** Use `umask` inside a subshell to strictly control permissions at
+creation time: `(umask 077; command > file)`.🧰 Tools
🪛 GitHub Check: Lint Documentation
[failure] 4-4: Line length
.jules/sentinel.md:4:81 MD013/line-length Line length [Expected: 80; Actual: 126] https://github.com/DavidAnson/markdownlint/blob/v0.34.0/doc/md013.md
[failure] 3-3: Line length
.jules/sentinel.md:3:81 MD013/line-length Line length [Expected: 80; Actual: 158] https://github.com/DavidAnson/markdownlint/blob/v0.34.0/doc/md013.md
[failure] 2-2: Line length
.jules/sentinel.md:2:81 MD013/line-length Line length [Expected: 80; Actual: 131] https://github.com/DavidAnson/markdownlint/blob/v0.34.0/doc/md013.md
[failure] 1-1: First line in a file should be a top-level heading
.jules/sentinel.md:1 MD041/first-line-heading/first-line-h1 First line in a file should be a top-level heading [Context: "## 2024-05-22 - Secure File Cr..."] https://github.com/DavidAnson/markdownlint/blob/v0.34.0/doc/md041.md
[failure] 1-1: Headings should be surrounded by blank lines
.jules/sentinel.md:1 MD022/blanks-around-headings Headings should be surrounded by blank lines [Expected: 1; Actual: 0; Below] [Context: "## 2024-05-22 - Secure File Creation in Shell Scripts"] https://github.com/DavidAnson/markdownlint/blob/v0.34.0/doc/md022.md
🤖 Prompt for AI Agents
In @.jules/sentinel.md around lines 1 - 4, Change the document heading to an H1
and add blank lines around it, and wrap long lines to satisfy MD041/MD022/MD013:
replace the first line "## 2024-05-22 - Secure File Creation in Shell Scripts"
with "# 2024-05-22 - Secure File Creation in Shell Scripts", ensure there is a
blank line before and after that H1, and reflow the longer sentences in the body
(e.g., the "Vulnerability", "Learning", and "Prevention" lines) so each line is
under the project's max line length (commonly 80 chars) while preserving the
content and bullet/heading structure.
1 participant
Fixed a TOCTOU race condition in
tools/setup-ssh-keys.shby usingumaskto ensure secure file permissions at creation time. Also added.jules/sentinel.mdwith the learning.PR created automatically by Jules for task 874749863381477520 started by @kidchenko
Summary by CodeRabbit
Release Notes
Documentation
Bug Fixes