Fix shell injection, AppleScript injection, and symlink escape in skill installer#43
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choisel wants to merge 5 commits intolcoutodemos:mainfrom
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Fix shell injection, AppleScript injection, and symlink escape in skill installer#43choisel wants to merge 5 commits intolcoutodemos:mainfrom
choisel wants to merge 5 commits intolcoutodemos:mainfrom
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added 5 commits
March 22, 2026 01:07
The curl|tar command was built as a shell string via execSync(), which passes through /bin/sh -c and allows shell metacharacters in path or tmpDir to be interpreted. Switch to two spawnSync() calls with explicit argument arrays: curl stdout is fed directly as stdin to tar, so no shell is ever involved and special characters cannot escape. Also removes the unused `dirname` import.
Building a shell command string dynamically and embedding it into an AppleScript `do script "..."` created an injection vector: a project path containing double quotes or AppleScript-significant characters could break out of the string context. Instead, write the shell command to a UUID-named temp file (mode 700) and pass only the file path to Terminal via AppleScript. The AppleScript string now contains no user-controlled data — only a /tmp/clui-term-<uuid>.sh path — so there is no injection surface. The temp file is cleaned up 5s after Terminal has had time to read it.
… helper Introduces vitest as test framework and adds two test suites: - shell-utils.test.ts: verifies shellSingleQuote correctly handles double quotes, dollar signs, backticks, backslashes, and the classic AppleScript injection payload without breaking the single-quote escaping invariant. - installer.test.ts: verifies that installGithubSkill passes curl and tar arguments as discrete array elements (not shell strings), that curl stdout is piped directly as tar stdin, and that non-zero exit codes from either binary surface as skill failures. Also extracts shellSingleQuote from the inline IPC handler into src/main/shell-utils.ts so it can be imported and tested independently.
Two-layer protection against malicious tarballs that contain symlinks pointing outside the extraction directory (e.g. to ~/.ssh/id_rsa): Layer 1 — prevention: pass --no-symlinks to tar so symlinks are never created during extraction on supported macOS/BSD tar versions. Layer 2 — detection: assertNoSymlinkEscape() walks the extracted tmpDir after tar completes and throws if any symlink resolves (via realpathSync, following full chains) to a path outside the base directory. This catches cases where --no-symlinks is silently ignored by older tar versions. Extraction fails fast and tmpDir is cleaned up on any escape detection. Adds symlink-escape.test.ts with 6 scenarios including nested symlinks, symlink chains, and path identification in error messages.
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Summary
Security audit identified three vulnerabilities in the skill installer and terminal opener. This PR fixes all three with tests.
Fix 1 — Shell injection in skill installer (
installer.ts)execSync()built acurl | tarcommand as a shell string, meaning special characters intmpDiror the skillpathcould be interpreted by/bin/sh. Replaced with twospawnSync()calls using explicit argument arrays — curl stdout is piped directly as tar stdin, no shell involved.Fix 2 — AppleScript injection in
openInTerminal(index.ts)A project path containing double quotes or AppleScript-significant characters could break out of the
do script "..."string context and execute arbitrary AppleScript. Instead, the shell command is written to a UUID-named temp file (/tmp/clui-term-<uuid>.sh, mode 700) and Terminal receives only the file path — no user-controlled data is ever embedded in the AppleScript string.Fix 3 — Symlink escape attack in tarball extraction (
installer.ts)A malicious GitHub tarball could include symlinks pointing outside the extraction directory (e.g. to
~/.ssh/id_rsa). Two-layer defence:--no-symlinksflag passed to tar, preventing symlink creation at extraction timeassertNoSymlinkEscape()walks the extractedtmpDirafter tar completes and throws if any symlink resolves (viarealpathSync, following full chains) to a path outside the base directoryTest infrastructure
No tests existed before this PR. Added vitest and three test suites (21 tests total):
shell-utils.test.ts— 9 tests forshellSingleQuotecovering double quotes,$, backticks, backslashes, and injection payloadsinstaller.test.ts— 5 tests verifyingspawnSyncargument arrays,--no-symlinkspresence, curl→tar stdin pipe, and error propagationsymlink-escape.test.ts— 7 tests forassertNoSymlinkEscapeusing real filesystem symlinks, including nested symlinks, symlink chains, and path identification in error messagesTest plan
npm install && npm test— all 21 tests pass