🛡️ Sentinel: [CRITICAL] Fix SSH key creation TOCTOU vulnerability #26
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Fixed a race condition where SSH private keys were briefly world-readable during creation. The `op read ... > file` command created the file with default permissions (often 644) before `chmod 600` was applied. Changes: - Modified `tools/setup-ssh-keys.sh` to use `(umask 077; ...)` subshells for sensitive file creation. - Added regression test `tests/test_ssh_creation.sh` to verify permissions. - Updated `build.sh` to include `tests/` in syntax checks. - Added security journal entry in `.jules/sentinel.md`. Verification: - Ran `tests/test_ssh_creation.sh` which confirmed correct permissions (600/700). - Ran `./build.sh` to verify syntax and linting. Co-authored-by: kidchenko <5432753+kidchenko@users.noreply.github.com>
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📝 WalkthroughWalkthroughThis PR addresses an SSH key creation security vulnerability by implementing and testing a mitigation. Changes include documentation of the race condition, a test script validating SSH key permissions, modifications to Changes
Estimated code review effort🎯 3 (Moderate) | ⏱️ ~20 minutes Poem
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Actionable comments posted: 2
🤖 Fix all issues with AI agents
In @.jules/sentinel.md:
- Around line 1-4: Update the entry header and fix markdownlint issues: change
the heading "## 2024-02-10 - [SSH Key Creation Race Condition]" to a top-level
heading and correct the date to "2026-02-10" (e.g. "# 2026-02-10 - [SSH Key
Creation Race Condition]"), ensure there is a blank line after that heading, and
reflow any lines longer than 80 characters (split the "Vulnerability",
"Learning", and "Prevention" lines into shorter sentences/paragraphs) so the
umask subshell recommendation "(umask 077; command > sensitive_file)" and other
text comply with MD013, MD022, and MD041.
In `@tests/test_ssh_creation.sh`:
- Around line 1-5: Add a cleanup function that removes TEST_DIR and register it
with trap so it runs on exit/failure (e.g., define cleanup() { rm -rf
"$TEST_DIR"; } and call trap cleanup EXIT or trap cleanup ERR EXIT) to ensure
temp dirs are removed when set -e causes early exit; reference the TEST_DIR
variable and remove the manual rm -rf "$TEST_DIR" at the end of the script so
the trap handles cleanup consistently.
🧹 Nitpick comments (1)
tests/test_ssh_creation.sh (1)
48-50: Test only covers therestorepath — consider noting this limitation.The test exercises
restorebut notgenerate,sync, or the interactive flow. This is fine for validating the TOCTOU fix, but worth noting if broader test coverage is planned.
| ## 2024-02-10 - [SSH Key Creation Race Condition] | ||
| **Vulnerability:** SSH private keys were briefly world-readable during creation because `umask` was not restricted. The `op read ... > file` command created the file with default permissions (often 644/664), and `chmod 600` was only applied afterward. | ||
| **Learning:** Shell redirection creates files before `chmod` runs. This creates a Time-of-Check to Time-of-Use (TOCTOU) window where sensitive data is exposed. | ||
| **Prevention:** Always wrap sensitive file creation commands in a subshell with restricted umask: `(umask 077; command > sensitive_file)`. This ensures the file is born secure. |
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Fix markdown lint failures flagged by CI and correct the year.
- The date reads
2024-02-10— should be2026-02-10. - CI reports several markdownlint violations: missing top-level heading (MD041), no blank line after heading (MD022), and lines exceeding 80 characters (MD013).
Proposed fix
-## 2024-02-10 - [SSH Key Creation Race Condition]
-**Vulnerability:** SSH private keys were briefly world-readable during creation because `umask` was not restricted. The `op read ... > file` command created the file with default permissions (often 644/664), and `chmod 600` was only applied afterward.
-**Learning:** Shell redirection creates files before `chmod` runs. This creates a Time-of-Check to Time-of-Use (TOCTOU) window where sensitive data is exposed.
-**Prevention:** Always wrap sensitive file creation commands in a subshell with restricted umask: `(umask 077; command > sensitive_file)`. This ensures the file is born secure.
+# Sentinel Journal
+
+## 2026-02-10 - SSH Key Creation Race Condition
+
+**Vulnerability:** SSH private keys were briefly world-readable during
+creation because `umask` was not restricted. The `op read ... > file`
+command created the file with default permissions (often 644/664), and
+`chmod 600` was only applied afterward.
+
+**Learning:** Shell redirection creates files before `chmod` runs. This
+creates a TOCTOU window where sensitive data is exposed.
+
+**Prevention:** Always wrap sensitive file creation in a subshell with
+restricted umask: `(umask 077; command > sensitive_file)`.📝 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.
| ## 2024-02-10 - [SSH Key Creation Race Condition] | |
| **Vulnerability:** SSH private keys were briefly world-readable during creation because `umask` was not restricted. The `op read ... > file` command created the file with default permissions (often 644/664), and `chmod 600` was only applied afterward. | |
| **Learning:** Shell redirection creates files before `chmod` runs. This creates a Time-of-Check to Time-of-Use (TOCTOU) window where sensitive data is exposed. | |
| **Prevention:** Always wrap sensitive file creation commands in a subshell with restricted umask: `(umask 077; command > sensitive_file)`. This ensures the file is born secure. | |
| # Sentinel Journal | |
| ## 2026-02-10 - SSH Key Creation Race Condition | |
| **Vulnerability:** SSH private keys were briefly world-readable during | |
| creation because `umask` was not restricted. The `op read ... > file` | |
| command created the file with default permissions (often 644/664), and | |
| `chmod 600` was only applied afterward. | |
| **Learning:** Shell redirection creates files before `chmod` runs. This | |
| creates a TOCTOU window where sensitive data is exposed. | |
| **Prevention:** Always wrap sensitive file creation in a subshell with | |
| restricted umask: `(umask 077; command > sensitive_file)`. |
🧰 Tools
🪛 GitHub Check: Lint Documentation
[failure] 4-4: Line length
.jules/sentinel.md:4:81 MD013/line-length Line length [Expected: 80; Actual: 176] 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: 159] 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: 251] 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: "## 2024-02-10 - [SSH Key Creat..."] 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: "## 2024-02-10 - [SSH Key Creation Race Condition]"] https://github.com/DavidAnson/markdownlint/blob/v0.34.0/doc/md022.md
🤖 Prompt for AI Agents
In @.jules/sentinel.md around lines 1 - 4, Update the entry header and fix
markdownlint issues: change the heading "## 2024-02-10 - [SSH Key Creation Race
Condition]" to a top-level heading and correct the date to "2026-02-10" (e.g. "#
2026-02-10 - [SSH Key Creation Race Condition]"), ensure there is a blank line
after that heading, and reflow any lines longer than 80 characters (split the
"Vulnerability", "Learning", and "Prevention" lines into shorter
sentences/paragraphs) so the umask subshell recommendation "(umask 077; command
> sensitive_file)" and other text comply with MD013, MD022, and MD041.
| #!/bin/bash | ||
| set -e | ||
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| # Setup test environment | ||
| TEST_DIR=$(mktemp -d) |
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Add a trap to ensure cleanup on failure.
With set -e, if any assertion fails the script exits immediately and rm -rf "$TEST_DIR" on line 85 is never reached, leaking temp directories.
Proposed fix
#!/bin/bash
set -e
# Setup test environment
TEST_DIR=$(mktemp -d)
+trap 'rm -rf "$TEST_DIR"' EXIT
export HOME="$TEST_DIR"And remove the manual cleanup at the end:
-# Cleanup
-rm -rf "$TEST_DIR"Also applies to: 84-85
🤖 Prompt for AI Agents
In `@tests/test_ssh_creation.sh` around lines 1 - 5, Add a cleanup function that
removes TEST_DIR and register it with trap so it runs on exit/failure (e.g.,
define cleanup() { rm -rf "$TEST_DIR"; } and call trap cleanup EXIT or trap
cleanup ERR EXIT) to ensure temp dirs are removed when set -e causes early exit;
reference the TEST_DIR variable and remove the manual rm -rf "$TEST_DIR" at the
end of the script so the trap handles cleanup consistently.
1 participant
This PR addresses a Time-of-Check to Time-of-Use (TOCTOU) vulnerability in
tools/setup-ssh-keys.shwhere SSH private keys were created with default umask permissions (often allowing group/world read) before being restricted withchmod 600.The fix wraps the file creation commands in a subshell with
umask 077, ensuring that files are born with secure permissions (600/700).Also includes:
tests/test_ssh_creation.shthat mocksopCLI to verify the fix.build.shto include thetests/directory in validation checks.PR created automatically by Jules for task 271437817872940856 started by @kidchenko
Summary by CodeRabbit
Bug Fixes
Tests