🛡️ Sentinel: [HIGH] Fix TOCTOU vulnerability in SSH key creation#24
🛡️ Sentinel: [HIGH] Fix TOCTOU vulnerability in SSH key creation#24
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- Use `umask 077` in a subshell when writing SSH private keys to disk. - Ensure SSH directory has 700 permissions on creation and if it already exists. - Add security journal entry in `.jules/sentinel.md`. This prevents a brief window where the private key file could be world-readable before `chmod 600` is applied. Co-authored-by: kidchenko <5432753+kidchenko@users.noreply.github.com>
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📝 WalkthroughWalkthroughDocumentation and code updates address SSH key file permission vulnerabilities. A sentinel entry documents a TOCTOU race condition in SSH private key creation with default permissions before chmod. The setup script now conditionally creates SSH directories with secure mode 700 and retrieves private keys within a restricted umask 077 environment. 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: 2
🤖 Fix all issues with AI agents
In @.jules/sentinel.md:
- Around line 2-4: The three long Markdown lines ("Vulnerability:", "Learning:",
"Prevention:") exceed the 80-character limit; reflow each paragraph to lines ≤80
chars by inserting line breaks at natural sentence or clause boundaries (e.g.,
after "race condition", after "umask", and before the example), keeping the
original headings and content intact and preserving the example command `(umask
077; command > file)` on its own wrapped line so the file complies with MD013.
- Line 1: Update the sentinel markdown: fix the date in the existing heading
from "2025-02-08" to "2026-02-08", add a top-level heading "# Sentinel" as the
first line to satisfy MD041, and insert a blank line between that top-level
heading and the "## 2026-02-08 - TOCTOU Race Condition in File Creation" entry
to satisfy MD022; ensure the second-level heading text is updated accordingly to
match the corrected date.
🧹 Nitpick comments (1)
tools/setup-ssh-keys.sh (1)
164-166: Public key file also created with default umask beforechmod.The public key isn't secret so this is low-risk, but for consistency with the private key hardening, you could wrap the public key write in a similar subshell pattern — e.g.,
(umask 133; op read ... > "$PUBLIC_KEY_FILE")to get0644immediately.
| @@ -0,0 +1,4 @@ | |||
| ## 2025-02-08 - TOCTOU Race Condition in File Creation | |||
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Date typo: should be 2026, not 2025.
The PR was created on 2026-02-08, but the heading says 2025-02-08.
Also, the markdown linter flags MD041 (first line should be a top-level # heading) and MD022 (blank line required after headings). Consider adding a top-level # Sentinel heading and a blank line before the ## entry.
Proposed fix
-## 2025-02-08 - TOCTOU Race Condition in File Creation
+# Sentinel
+
+## 2026-02-08 - TOCTOU Race Condition in File Creation
+📝 Committable suggestion
‼️ IMPORTANT
Carefully review the code before committing. Ensure that it accurately replaces the highlighted code, contains no missing lines, and has no issues with indentation. Thoroughly test & benchmark the code to ensure it meets the requirements.
| ## 2025-02-08 - TOCTOU Race Condition in File Creation | |
| # Sentinel | |
| ## 2026-02-08 - TOCTOU Race Condition in File Creation | |
🧰 Tools
🪛 GitHub Check: Lint Documentation
[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: "## 2025-02-08 - TOCTOU Race Co..."] 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: "## 2025-02-08 - TOCTOU Race Condition in File Creation"] https://github.com/DavidAnson/markdownlint/blob/v0.34.0/doc/md022.md
🤖 Prompt for AI Agents
In @.jules/sentinel.md at line 1, Update the sentinel markdown: fix the date in
the existing heading from "2025-02-08" to "2026-02-08", add a top-level heading
"# Sentinel" as the first line to satisfy MD041, and insert a blank line between
that top-level heading and the "## 2026-02-08 - TOCTOU Race Condition in File
Creation" entry to satisfy MD022; ensure the second-level heading text is
updated accordingly to match the corrected date.
| **Vulnerability:** The SSH private key was being created with default permissions (potentially world-readable) before `chmod 600` was applied. This created a race condition where the key could be read by other users on the system. | ||
| **Learning:** Shell redirection (`>`) creates files with the current `umask` before any subsequent `chmod` command is executed. | ||
| **Prevention:** Use `umask 077` in a subshell when creating sensitive files to ensure they are created with restricted permissions from the start. Example: `(umask 077; command > file)`. |
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Markdown lint: line length exceeds 80 characters (MD013).
Lines 2–4 all exceed the 80-character limit flagged by the linter. Wrap the long lines to comply.
🧰 Tools
🪛 GitHub Check: Lint Documentation
[failure] 4-4: Line length
.jules/sentinel.md:4:81 MD013/line-length Line length [Expected: 80; Actual: 186] 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: 127] 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: 230] https://github.com/DavidAnson/markdownlint/blob/v0.34.0/doc/md013.md
🤖 Prompt for AI Agents
In @.jules/sentinel.md around lines 2 - 4, The three long Markdown lines
("Vulnerability:", "Learning:", "Prevention:") exceed the 80-character limit;
reflow each paragraph to lines ≤80 chars by inserting line breaks at natural
sentence or clause boundaries (e.g., after "race condition", after "umask", and
before the example), keeping the original headings and content intact and
preserving the example command `(umask 077; command > file)` on its own wrapped
line so the file complies with MD013.
1 participant
🛡️ Sentinel: [HIGH] Fix TOCTOU vulnerability in SSH key creation
🚨 Severity: HIGH
💡 Vulnerability: The SSH private key was being created with default permissions (potentially world-readable) before
chmod 600was applied. This created a Time-of-Check Time-of-Use (TOCTOU) race condition where the key could be read by other users on the system during the window between creation and permission modification.🎯 Impact: An attacker with local access could potentially read the private key during the race condition window, compromising the user's SSH access.
🔧 Fix:
(umask 077; command > file)pattern to ensure the file is created with restricted permissions (-rw-------) atomically.mkdir -p -m 700and enforcedchmod 700even if the directory already exists.✅ Verification:
umask(often 022).bash -n.PR created automatically by Jules for task 11977943561005832187 started by @kidchenko
Summary by CodeRabbit