🛡️ Sentinel: Fix TOCTOU race condition in SSH key setup #25
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Wrap sensitive file and directory creation in `tools/setup-ssh-keys.sh` with `umask 077` in a subshell. This ensures that SSH keys and directories are created with secure permissions (600/700) immediately, eliminating the window of vulnerability where they might be world-readable before `chmod` is called. Also adds Sentinel's journal entry in `.jules/sentinel.md`. Co-authored-by: kidchenko <5432753+kidchenko@users.noreply.github.com>
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📝 WalkthroughWalkthroughA new security documentation file was added detailing a TOCTOU race condition vulnerability in SSH key setup. The setup script was updated to apply restrictive umask (077) when creating the SSH directory and retrieving private keys from 1Password, eliminating the window of exposure before chmod operations. Changes
Estimated code review effort🎯 2 (Simple) | ⏱️ ~12 minutes Poem
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Actionable comments posted: 1
🤖 Fix all issues with AI agents
In @.jules/sentinel.md:
- Around line 3-6: The heading line "2024-05-22 - TOCTOU Race Condition in File
Creation" needs three fixes: insert a blank line immediately below the heading
to satisfy MD022; reflow the long description lines (the lines describing the
vulnerability, learning, and prevention that reference tools/setup-ssh-keys.sh
and umask 077) so each line is ≤80 characters to satisfy MD013; and update the
date prefix from "2024-05-22" to the correct February 2026 date (e.g.
"2026-02-<day>") to reflect the PR creation date. Locate that heading and the
three following paragraph lines in .jules/sentinel.md and apply these edits.
🧹 Nitpick comments (2)
tools/setup-ssh-keys.sh (2)
152-155: The conditional aroundmkdir -pis unnecessary and slightly ironic.
mkdir -pis idempotent — it succeeds whether the directory exists or not. Wrapping it in an existence check re-introduces a (benign) TOCTOU gap: between the-dtest and themkdir, another process could remove the directory. Simplifying to always run the subshell is cleaner and still safe:Suggested simplification
- if [[ ! -d "$SSH_DIR" ]]; then - (umask 077 && mkdir -p "$SSH_DIR") - fi - chmod 700 "$SSH_DIR" + (umask 077 && mkdir -p "$SSH_DIR") + chmod 700 "$SSH_DIR"
164-166: Public key is intentionally written withoutumaskprotection — worth a brief inline comment.Since the private key path right above is carefully wrapped in a restrictive subshell, a reader might wonder whether the public key was overlooked. A one-line comment (e.g.,
# Public key is non-sensitive; 644 is intentional) would prevent future "fix" attempts.
| ## 2024-05-22 - TOCTOU Race Condition in File Creation | ||
| **Vulnerability:** Found a Time-of-Check to Time-of-Use (TOCTOU) vulnerability in `tools/setup-ssh-keys.sh` where sensitive SSH keys were created with default permissions (potentially world-readable) before being restricted with `chmod`. | ||
| **Learning:** Even with a subsequent `chmod`, there is a small window where a file is accessible to other users on the system if created with default `umask`. | ||
| **Prevention:** Always use `umask 077` in a subshell when creating sensitive files or directories to ensure they are private from the moment of creation. |
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Fix markdown lint failures flagged by CI.
The Lint Documentation check is failing on this file with four violations:
- MD022 (Line 3): Missing blank line below the heading.
- MD013 (Lines 4–6): Lines exceed the 80-character limit.
Also, the date 2024-05-22 appears incorrect — this PR was created in February 2026.
Suggested rewrite to fix all lint issues
# Sentinel's Journal
-## 2024-05-22 - TOCTOU Race Condition in File Creation
-**Vulnerability:** Found a Time-of-Check to Time-of-Use (TOCTOU) vulnerability in `tools/setup-ssh-keys.sh` where sensitive SSH keys were created with default permissions (potentially world-readable) before being restricted with `chmod`.
-**Learning:** Even with a subsequent `chmod`, there is a small window where a file is accessible to other users on the system if created with default `umask`.
-**Prevention:** Always use `umask 077` in a subshell when creating sensitive files or directories to ensure they are private from the moment of creation.
+## 2026-02-09 - TOCTOU Race Condition in File Creation
+
+**Vulnerability:** Found a TOCTOU vulnerability in
+`tools/setup-ssh-keys.sh` where sensitive SSH keys were created
+with default permissions (potentially world-readable) before
+being restricted with `chmod`.
+
+**Learning:** Even with a subsequent `chmod`, there is a small
+window where a file is accessible to other users on the system
+if created with default `umask`.
+
+**Prevention:** Always use `umask 077` in a subshell when
+creating sensitive files or directories to ensure they are
+private from the moment of 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.
| ## 2024-05-22 - TOCTOU Race Condition in File Creation | |
| **Vulnerability:** Found a Time-of-Check to Time-of-Use (TOCTOU) vulnerability in `tools/setup-ssh-keys.sh` where sensitive SSH keys were created with default permissions (potentially world-readable) before being restricted with `chmod`. | |
| **Learning:** Even with a subsequent `chmod`, there is a small window where a file is accessible to other users on the system if created with default `umask`. | |
| **Prevention:** Always use `umask 077` in a subshell when creating sensitive files or directories to ensure they are private from the moment of creation. | |
| # Sentinel's Journal | |
| ## 2026-02-09 - TOCTOU Race Condition in File Creation | |
| **Vulnerability:** Found a TOCTOU vulnerability in | |
| `tools/setup-ssh-keys.sh` where sensitive SSH keys were created | |
| with default permissions (potentially world-readable) before | |
| being restricted with `chmod`. | |
| **Learning:** Even with a subsequent `chmod`, there is a small | |
| window where a file is accessible to other users on the system | |
| if created with default `umask`. | |
| **Prevention:** Always use `umask 077` in a subshell when | |
| creating sensitive files or directories to ensure they are | |
| private from the moment of creation. |
🧰 Tools
🪛 GitHub Check: Lint Documentation
[failure] 6-6: Line length
.jules/sentinel.md:6:81 MD013/line-length Line length [Expected: 80; Actual: 153] https://github.com/DavidAnson/markdownlint/blob/v0.34.0/doc/md013.md
[failure] 5-5: Line length
.jules/sentinel.md:5:81 MD013/line-length Line length [Expected: 80; Actual: 158] https://github.com/DavidAnson/markdownlint/blob/v0.34.0/doc/md013.md
[failure] 4-4: Line length
.jules/sentinel.md:4:81 MD013/line-length Line length [Expected: 80; Actual: 237] https://github.com/DavidAnson/markdownlint/blob/v0.34.0/doc/md013.md
[failure] 3-3: Headings should be surrounded by blank lines
.jules/sentinel.md:3 MD022/blanks-around-headings Headings should be surrounded by blank lines [Expected: 1; Actual: 0; Below] [Context: "## 2024-05-22 - 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 around lines 3 - 6, The heading line "2024-05-22 - TOCTOU
Race Condition in File Creation" needs three fixes: insert a blank line
immediately below the heading to satisfy MD022; reflow the long description
lines (the lines describing the vulnerability, learning, and prevention that
reference tools/setup-ssh-keys.sh and umask 077) so each line is ≤80 characters
to satisfy MD013; and update the date prefix from "2024-05-22" to the correct
February 2026 date (e.g. "2026-02-<day>") to reflect the PR creation date.
Locate that heading and the three following paragraph lines in
.jules/sentinel.md and apply these edits.
1 participant
🛡️ Sentinel: [HIGH] Fix TOCTOU race condition in SSH key setup
🚨 Severity: HIGH
💡 Vulnerability: Time-of-Check to Time-of-Use (TOCTOU) race condition where SSH keys were created with default permissions (potentially world-readable) before being restricted.
🎯 Impact: A malicious local user could potentially read the private key in the brief window between file creation and permission restriction.
🔧 Fix: Wrapped file and directory creation in a subshell with
umask 077to ensure secure permissions from the moment of creation.✅ Verification: Verified behavior with a reproduction script and confirmed syntax correctness with
./build.sh.PR created automatically by Jules for task 5605279102137415722 started by @kidchenko
Summary by CodeRabbit
Bug Fixes
Documentation