🛡️ Sentinel: Fix SSH key creation race condition #20
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Wrapping the private key file creation in a subshell with `umask 077` ensures the file is created with restricted permissions (0600) atomically, preventing a window where it might be world-readable. - tools/setup-ssh-keys.sh: Use umask 077 for private key creation - .jules/sentinel.md: Record security learning Co-authored-by: kidchenko <5432753+kidchenko@users.noreply.github.com>
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📝 WalkthroughWalkthroughA TOCTOU vulnerability in SSH key file handling was documented and fixed. The code change modifies the private key restoration process to use 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: Update the markdown to satisfy the linter: change the first
heading from "## 2024-10-24 - Shell Script Race Conditions" to a top-level
heading using "#" and add a blank line after it, then wrap or break long lines
(lines describing Vulnerability, Learning, and Prevention) so they are <=80
characters; keep the same content but reflow text or split into multiple short
lines and ensure the code reference `tools/setup-ssh-keys.sh` and the
recommendation `umask 077`/`chmod` remain intact.
| ## 2024-10-24 - Shell Script Race Conditions | ||
| **Vulnerability:** Found a Time-of-Check Time-of-Use (TOCTOU) race condition in `tools/setup-ssh-keys.sh` where a private key was written to disk with default permissions before being restricted with `chmod`. | ||
| **Learning:** Shell scripts often default to permissive `umask` (e.g., 022), making files world-readable for a brief window during creation. | ||
| **Prevention:** Always use `umask 077` in a subshell before writing sensitive files to ensure they are created with restricted permissions (0600) atomically. |
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Fix markdown linting failures flagged by CI.
The documentation content is accurate, but the linter reports several issues:
- MD041: First line should be a top-level heading (
#not##) - MD022: Heading needs a blank line after it
- MD013: Lines 2-4 exceed 80 characters
📝 Proposed fix to address linting issues
-## 2024-10-24 - Shell Script Race Conditions
-**Vulnerability:** Found a Time-of-Check Time-of-Use (TOCTOU) race condition in `tools/setup-ssh-keys.sh` where a private key was written to disk with default permissions before being restricted with `chmod`.
-**Learning:** Shell scripts often default to permissive `umask` (e.g., 022), making files world-readable for a brief window during creation.
-**Prevention:** Always use `umask 077` in a subshell before writing sensitive files to ensure they are created with restricted permissions (0600) atomically.
+# Sentinel Security Learnings
+
+## 2024-10-24 - Shell Script Race Conditions
+
+**Vulnerability:** Found a Time-of-Check Time-of-Use (TOCTOU) race condition
+in `tools/setup-ssh-keys.sh` where a private key was written to disk with
+default permissions before being restricted with `chmod`.
+
+**Learning:** Shell scripts often default to permissive `umask` (e.g., 022),
+making files world-readable for a brief window during creation.
+
+**Prevention:** Always use `umask 077` in a subshell before writing sensitive
+files to ensure they are created with restricted permissions (0600) atomically.📝 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.
| ## 2024-10-24 - Shell Script Race Conditions | |
| **Vulnerability:** Found a Time-of-Check Time-of-Use (TOCTOU) race condition in `tools/setup-ssh-keys.sh` where a private key was written to disk with default permissions before being restricted with `chmod`. | |
| **Learning:** Shell scripts often default to permissive `umask` (e.g., 022), making files world-readable for a brief window during creation. | |
| **Prevention:** Always use `umask 077` in a subshell before writing sensitive files to ensure they are created with restricted permissions (0600) atomically. | |
| # Sentinel Security Learnings | |
| ## 2024-10-24 - Shell Script Race Conditions | |
| **Vulnerability:** Found a Time-of-Check Time-of-Use (TOCTOU) race condition | |
| in `tools/setup-ssh-keys.sh` where a private key was written to disk with | |
| default permissions before being restricted with `chmod`. | |
| **Learning:** Shell scripts often default to permissive `umask` (e.g., 022), | |
| making files world-readable for a brief window during creation. | |
| **Prevention:** Always use `umask 077` in a subshell before writing sensitive | |
| files to ensure they are created with restricted permissions (0600) atomically. |
🧰 Tools
🪛 GitHub Check: Lint Documentation
[failure] 4-4: Line length
.jules/sentinel.md:4:81 MD013/line-length Line length [Expected: 80; Actual: 157] 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: 140] 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: 208] 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: "## 2024-10-24 - Shell Script R..."] 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: "## 2024-10-24 - Shell Script Race Conditions"] 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 markdown to satisfy the
linter: change the first heading from "## 2024-10-24 - Shell Script Race
Conditions" to a top-level heading using "#" and add a blank line after it, then
wrap or break long lines (lines describing Vulnerability, Learning, and
Prevention) so they are <=80 characters; keep the same content but reflow text
or split into multiple short lines and ensure the code reference
`tools/setup-ssh-keys.sh` and the recommendation `umask 077`/`chmod` remain
intact.
1 participant
🛡️ Sentinel: [CRITICAL] Fix TOCTOU race condition in SSH key setup
🚨 Severity: CRITICAL
💡 Vulnerability: Time-of-Check Time-of-Use (TOCTOU) race condition where SSH private key was written with default permissions before being restricted.
🎯 Impact: On a multi-user system, an attacker could potentially read the private key during the brief window between file creation and
chmod.🔧 Fix: Wrapped the file creation in a subshell with
umask 077to ensure atomic 0600 permissions.✅ Verification: Verified syntax with
bash -nand visual inspection. Theumask 077guarantees the file is created with read/write access for the owner only.PR created automatically by Jules for task 13455434870920061545 started by @kidchenko
Summary by CodeRabbit
Bug Fixes
Documentation