🛡️ Sentinel: [CRITICAL] Fix insecure private key file creation #23
Conversation
🚨 Severity: CRITICAL 💡 Vulnerability: Private SSH keys were being created with default umask permissions (often 0644) before being restricted to 0600. This created a race condition (TOCTOU) where the file could be read by other users during the creation window. 🎯 Impact: Potential leakage of private SSH keys to other users on the same system. 🔧 Fix: Wrapped the private key file creation in a subshell with `umask 077` to ensure the file is created with 0600 permissions from the start. ✅ Verification: Verified with a reproduction script that files are now created with 0600 permissions immediately. Ran `bash -n tools/setup-ssh-keys.sh` to ensure syntax correctness. Co-authored-by: kidchenko <5432753+kidchenko@users.noreply.github.com>
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📝 WalkthroughWalkthroughThis pull request addresses a TOCTOU (Time-of-Check-Time-of-Use) security vulnerability in private SSH key file creation. A new documentation file documents the vulnerability pattern, and the setup script is updated to use umask 077 within a subshell to ensure restrictive permissions on sensitive files from creation. Changes
Estimated code review effort🎯 2 (Simple) | ⏱️ ~12 minutes Poem
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🧪 Generate unit tests (beta)
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Actionable comments posted: 2
🤖 Fix all issues with AI agents
In @.jules/sentinel.md:
- Line 1: Update the sentinel entry header that currently reads "## 2025-02-07 -
Insecure File Creation for Sensitive Data" to the correct date "2026-02-07" so
the heading matches the PR creation date; locate the Markdown header string and
change the year from 2025 to 2026.
- Around line 1-4: Change the first line to a top-level heading by replacing the
"## 2025-02-07 - Insecure File Creation for Sensitive Data" line with "#
2025-02-07 - Insecure File Creation for Sensitive Data", add a blank line
immediately after that heading to satisfy MD022, and reflow/wrap the long
sentences in the following lines (the description and prevention lines) to 80
characters or fewer per line to fix MD013—split them into short sentences or
separate bullet points while keeping the same content (refer to the heading text
and the "Prevention" sentence about "umask 077"/"umask 0177" to locate where to
wrap).
| @@ -0,0 +1,4 @@ | |||
| ## 2025-02-07 - Insecure File Creation for Sensitive Data | |||
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Date appears to have a typo: 2025 should be 2026.
The PR was created on 2026-02-07, but the heading says 2025-02-07.
🧰 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: "## 2025-02-07 - Insecure File ..."] 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: "## 2025-02-07 - Insecure File Creation for Sensitive Data"] 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 entry header that
currently reads "## 2025-02-07 - Insecure File Creation for Sensitive Data" to
the correct date "2026-02-07" so the heading matches the PR creation date;
locate the Markdown header string and change the year from 2025 to 2026.
| ## 2025-02-07 - Insecure File Creation for Sensitive Data | ||
| **Vulnerability:** Private SSH keys were created with default umask permissions (often 0644 or 0664) before being restricted to 0600, creating a race condition (TOCTOU) where the file could be read by other users during the creation window. | ||
| **Learning:** Shell redirection (`>`) creates the file before `chmod` is executed, using the process's default umask. Explicitly setting `chmod` afterwards is insufficient for highly sensitive files on multi-user systems. | ||
| **Prevention:** Wrap sensitive file creation commands in a subshell with `umask 077` (or `umask 0177` for executable scripts) to ensure the file is created with restrictive permissions (0600) from the start. |
There was a problem hiding this comment.
Fix markdown lint failures flagged by the CI pipeline.
The Lint Documentation check is failing with multiple violations:
- MD041: First line should be a top-level heading (
#), not##. - MD022: Heading on line 1 needs a blank line below it.
- MD013: Lines 2–4 exceed the 80-character line limit.
Proposed fix
-## 2025-02-07 - Insecure File Creation for Sensitive Data
-**Vulnerability:** Private SSH keys were created with default umask permissions (often 0644 or 0664) before being restricted to 0600, creating a race condition (TOCTOU) where the file could be read by other users during the creation window.
-**Learning:** Shell redirection (`>`) creates the file before `chmod` is executed, using the process's default umask. Explicitly setting `chmod` afterwards is insufficient for highly sensitive files on multi-user systems.
-**Prevention:** Wrap sensitive file creation commands in a subshell with `umask 077` (or `umask 0177` for executable scripts) to ensure the file is created with restrictive permissions (0600) from the start.
+# Sentinel
+
+## 2026-02-07 - Insecure File Creation for Sensitive Data
+
+**Vulnerability:** Private SSH keys were created with default umask
+permissions (often 0644 or 0664) before being restricted to 0600,
+creating a race condition (TOCTOU) where the file could be read by
+other users during the creation window.
+
+**Learning:** Shell redirection (`>`) creates the file before `chmod`
+is executed, using the process's default umask. Explicitly setting
+`chmod` afterward is insufficient for highly sensitive files on
+multi-user systems.
+
+**Prevention:** Wrap sensitive file creation commands in a subshell
+with `umask 077` (or `umask 0177` for executable scripts) to ensure
+the file is created with restrictive permissions (0600) from the
+start.📝 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.
| ## 2025-02-07 - Insecure File Creation for Sensitive Data | |
| **Vulnerability:** Private SSH keys were created with default umask permissions (often 0644 or 0664) before being restricted to 0600, creating a race condition (TOCTOU) where the file could be read by other users during the creation window. | |
| **Learning:** Shell redirection (`>`) creates the file before `chmod` is executed, using the process's default umask. Explicitly setting `chmod` afterwards is insufficient for highly sensitive files on multi-user systems. | |
| **Prevention:** Wrap sensitive file creation commands in a subshell with `umask 077` (or `umask 0177` for executable scripts) to ensure the file is created with restrictive permissions (0600) from the start. | |
| # Sentinel | |
| ## 2026-02-07 - Insecure File Creation for Sensitive Data | |
| **Vulnerability:** Private SSH keys were created with default umask | |
| permissions (often 0644 or 0664) before being restricted to 0600, | |
| creating a race condition (TOCTOU) where the file could be read by | |
| other users during the creation window. | |
| **Learning:** Shell redirection (`>`) creates the file before `chmod` | |
| is executed, using the process's default umask. Explicitly setting | |
| `chmod` afterward is insufficient for highly sensitive files on | |
| multi-user systems. | |
| **Prevention:** Wrap sensitive file creation commands in a subshell | |
| with `umask 077` (or `umask 0177` for executable scripts) to ensure | |
| the file is created with restrictive permissions (0600) from the | |
| start. |
🧰 Tools
🪛 GitHub Check: Lint Documentation
[failure] 4-4: Line length
.jules/sentinel.md:4:81 MD013/line-length Line length [Expected: 80; Actual: 207] 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: 221] 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: 240] 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: "## 2025-02-07 - Insecure File ..."] 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: "## 2025-02-07 - Insecure File Creation for Sensitive Data"] https://github.com/DavidAnson/markdownlint/blob/v0.34.0/doc/md022.md
🪛 LanguageTool
[locale-violation] ~3-~3: In American English, ‘afterward’ is the preferred variant. ‘Afterwards’ is more commonly used in British English and other dialects.
Context: ...fault umask. Explicitly setting chmod afterwards is insufficient for highly sensitive fi...
(AFTERWARDS_US)
🤖 Prompt for AI Agents
In @.jules/sentinel.md around lines 1 - 4, Change the first line to a top-level
heading by replacing the "## 2025-02-07 - Insecure File Creation for Sensitive
Data" line with "# 2025-02-07 - Insecure File Creation for Sensitive Data", add
a blank line immediately after that heading to satisfy MD022, and reflow/wrap
the long sentences in the following lines (the description and prevention lines)
to 80 characters or fewer per line to fix MD013—split them into short sentences
or separate bullet points while keeping the same content (refer to the heading
text and the "Prevention" sentence about "umask 077"/"umask 0177" to locate
where to wrap).
1 participant
This PR addresses a critical security vulnerability in
tools/setup-ssh-keys.shwhere private SSH keys were briefly world-readable during creation.Changes:
tools/setup-ssh-keys.shto useumask 077in a subshell when writing the private key..jules/sentinel.mdto document this security learning.PR created automatically by Jules for task 3100625607909715068 started by @kidchenko
Summary by CodeRabbit
Bug Fixes
Documentation