🛡️ Sentinel: Fix insecure SSH key creation permissions#29
🛡️ Sentinel: Fix insecure SSH key creation permissions#29
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Prevent TOCTOU race condition where private keys were briefly world-readable during creation. Use subshell with `umask 077` for atomic permissions. - Wraps `mkdir` and file creation in `(umask 077; ...)` - Removes existing files before writing to ensure new inode creation - Adds Sentinel journal entry regarding secure file creation Co-authored-by: kidchenko <5432753+kidchenko@users.noreply.github.com>
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📝 WalkthroughWalkthroughThese changes address a security vulnerability in SSH key generation by implementing strict umask controls and atomic file creation practices. SSH directory creation now uses permission-restricted approaches, and existing key files are removed prior to restoration to ensure newly created files have correct restrictive permissions. Changes
Estimated code review effort🎯 2 (Simple) | ⏱️ ~18 minutes Poem
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Actionable comments posted: 1
🤖 Fix all issues with AI agents
In @.jules/sentinel.md:
- Around line 3-6: Update the markdown to satisfy lint rules: change the heading
date from "2025-02-13" to "2026-02-13", add a blank line immediately after the
"## 2026-02-13 - Secure File Creation in Shell Scripts" heading to fix MD022,
and reflow the long lines in the three following bullet paragraphs so no line
exceeds 80 characters (split sentences or reorder phrases) to fix MD013 while
preserving the original content about umask, redirection, mkdir and chmod;
ensure the examples `(umask 077 && mkdir ...)` and `(umask 077; command > file)`
remain intact.
🧹 Nitpick comments (1)
tools/setup-ssh-keys.sh (1)
157-170: Consider: both key files are deleted before any 1Password call succeeds.If
op readfor the private key (Line 164) fails,set -ewill terminate the script — but both the private and public key files have already been removed on Line 158. The user ends up with no local keys at all. Since the keys live in 1Password this is recoverable, but you could mitigate by deferring therm -fto just before each respective write, or deleting only the private key before the private-key write and the public key before the public-key write.This is a minor resilience nit given
set -eand the 1Password backup, so feel free to defer.
| ## 2025-02-13 - Secure File Creation in Shell Scripts | ||
| **Vulnerability:** SSH private keys were created with default umask (often 022, resulting in 644/world-readable) before being restricted with `chmod 600`. This created a race condition where the key was briefly readable by other users. | ||
| **Learning:** Shell redirection (`>`) and `mkdir` adhere to the process's `umask` at the time of execution. `chmod` after creation leaves a window of vulnerability. | ||
| **Prevention:** Use `(umask 077 && mkdir ...)` for directories and `(umask 077; command > file)` for files to ensure atomic secure permissions. Remove existing files before writing if sensitive to ensure new inode creation with correct permissions. |
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Fix markdown lint failures flagged by CI.
The documentation lint check is failing with:
- MD022 (Line 3): Missing blank line below the
##heading. - MD013 (Lines 4–6): Lines exceed the 80-character limit.
Also, the date reads 2025-02-13 — should this be 2026-02-13 to match the PR date?
Proposed fix
-## 2025-02-13 - Secure File Creation in Shell Scripts
-**Vulnerability:** SSH private keys were created with default umask (often 022, resulting in 644/world-readable) before being restricted with `chmod 600`. This created a race condition where the key was briefly readable by other users.
-**Learning:** Shell redirection (`>`) and `mkdir` adhere to the process's `umask` at the time of execution. `chmod` after creation leaves a window of vulnerability.
-**Prevention:** Use `(umask 077 && mkdir ...)` for directories and `(umask 077; command > file)` for files to ensure atomic secure permissions. Remove existing files before writing if sensitive to ensure new inode creation with correct permissions.
+## 2026-02-13 - Secure File Creation in Shell Scripts
+
+**Vulnerability:** SSH private keys were created with default umask
+(often 022, resulting in 644/world-readable) before being restricted
+with `chmod 600`. This created a race condition where the key was
+briefly readable by other users.
+
+**Learning:** Shell redirection (`>`) and `mkdir` adhere to the
+process's `umask` at the time of execution. `chmod` after creation
+leaves a window of vulnerability.
+
+**Prevention:** Use `(umask 077 && mkdir ...)` for directories and
+`(umask 077; command > file)` for files to ensure atomic secure
+permissions. Remove existing files before writing if sensitive to
+ensure new inode creation with correct permissions.📝 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.
| ## 2025-02-13 - Secure File Creation in Shell Scripts | |
| **Vulnerability:** SSH private keys were created with default umask (often 022, resulting in 644/world-readable) before being restricted with `chmod 600`. This created a race condition where the key was briefly readable by other users. | |
| **Learning:** Shell redirection (`>`) and `mkdir` adhere to the process's `umask` at the time of execution. `chmod` after creation leaves a window of vulnerability. | |
| **Prevention:** Use `(umask 077 && mkdir ...)` for directories and `(umask 077; command > file)` for files to ensure atomic secure permissions. Remove existing files before writing if sensitive to ensure new inode creation with correct permissions. | |
| ## 2026-02-13 - Secure File Creation in Shell Scripts | |
| **Vulnerability:** SSH private keys were created with default umask | |
| (often 022, resulting in 644/world-readable) before being restricted | |
| with `chmod 600`. This created a race condition where the key was | |
| briefly readable by other users. | |
| **Learning:** Shell redirection (`>`) and `mkdir` adhere to the | |
| process's `umask` at the time of execution. `chmod` after creation | |
| leaves a window of vulnerability. | |
| **Prevention:** Use `(umask 077 && mkdir ...)` for directories and | |
| `(umask 077; command > file)` for files to ensure atomic secure | |
| permissions. Remove existing files before writing if sensitive to | |
| ensure new inode creation with correct permissions. |
🧰 Tools
🪛 GitHub Check: Lint Documentation
[failure] 6-6: Line length
.jules/sentinel.md:6:81 MD013/line-length Line length [Expected: 80; Actual: 248] 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: 164] 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: 235] 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: "## 2025-02-13 - Secure File Creation in Shell Scripts"] https://github.com/DavidAnson/markdownlint/blob/v0.34.0/doc/md022.md
🤖 Prompt for AI Agents
In @.jules/sentinel.md around lines 3 - 6, Update the markdown to satisfy lint
rules: change the heading date from "2025-02-13" to "2026-02-13", add a blank
line immediately after the "## 2026-02-13 - Secure File Creation in Shell
Scripts" heading to fix MD022, and reflow the long lines in the three following
bullet paragraphs so no line exceeds 80 characters (split sentences or reorder
phrases) to fix MD013 while preserving the original content about umask,
redirection, mkdir and chmod; ensure the examples `(umask 077 && mkdir ...)` and
`(umask 077; command > file)` remain intact.
1 participant
🛡️ Sentinel: [CRITICAL/HIGH] Fix Secure SSH Key Creation
🚨 Severity: HIGH
💡 Vulnerability: Race condition (TOCTOU) in SSH key creation. Private keys were created with default umask permissions (often 644/world-readable) before being restricted with
chmod 600. This left a brief window where other users on the system could read the private key.🎯 Impact: Potential exposure of private SSH keys to other local users on a shared machine.
🔧 Fix:
mkdir -pin a subshell withumask 077.op read ... > filein a subshell withumask 077.rm -ffor existing files to ensure new files are created with correct permissions rather than truncating existing files with potentially insecure permissions.✅ Verification:
umaskare world-readable, while those created with(umask 077; ...)are restricted to owner-only (600).bash -n.PR created automatically by Jules for task 15876976491062478903 started by @kidchenko
Summary by CodeRabbit
Documentation
Bug Fixes