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fix(security): eliminate TOCTOU race conditions in ssl-bump.ts #1159

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Merged
Mossaka merged 1 commit into from
Mar 5, 2026
Merged

fix(security): eliminate TOCTOU race conditions in ssl-bump.ts #1159

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31 changes: 15 additions & 16 deletions src/ssl-bump.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -167,10 +167,9 @@ export async function generateSessionCa(config: SslBumpConfig): Promise<CaFiles>
const { workDir, commonName = 'AWF Session CA', validityDays = 1 } = config;

// Create ssl directory in workDir, backed by tmpfs when possible
// Use recursive:true which is a no-op if the directory already exists (avoids TOCTOU)
const sslDir = path.join(workDir, 'ssl');
if (!fs.existsSync(sslDir)) {
fs.mkdirSync(sslDir, { recursive: true, mode: 0o700 });
}
fs.mkdirSync(sslDir, { recursive: true, mode: 0o700 });

// Attempt to mount tmpfs so keys never touch disk
const usingTmpfs = await mountSslTmpfs(sslDir);
Expand Down Expand Up @@ -254,24 +253,24 @@ export async function initSslDb(workDir: string): Promise<string> {
const indexPath = path.join(sslDbPath, 'index.txt');
const sizePath = path.join(sslDbPath, 'size');

// Create the database structure
if (!fs.existsSync(sslDbPath)) {
fs.mkdirSync(sslDbPath, { recursive: true, mode: 0o700 });
}
// Create the database structure (recursive:true is a no-op if dir exists, avoids TOCTOU)
fs.mkdirSync(sslDbPath, { recursive: true, mode: 0o700 });

// Create certs subdirectory
if (!fs.existsSync(certsPath)) {
fs.mkdirSync(certsPath, { mode: 0o700 });
}
fs.mkdirSync(certsPath, { recursive: true, mode: 0o700 });

// Create index.txt (empty file for certificate index)
if (!fs.existsSync(indexPath)) {
fs.writeFileSync(indexPath, '', { mode: 0o600 });
// Create index.txt atomically — 'wx' flag (O_WRONLY|O_CREAT|O_EXCL) fails if file exists
try {
fs.writeFileSync(indexPath, '', { mode: 0o600, flag: 'wx' });
} catch (err: unknown) {
if ((err as NodeJS.ErrnoException).code !== 'EEXIST') throw err;
}

// Create size file (tracks current DB size, starts at 0)
if (!fs.existsSync(sizePath)) {
fs.writeFileSync(sizePath, '0\n', { mode: 0o600 });
// Create size file atomically
try {
fs.writeFileSync(sizePath, '0\n', { mode: 0o600, flag: 'wx' });
} catch (err: unknown) {
if ((err as NodeJS.ErrnoException).code !== 'EEXIST') throw err;
}

logger.debug(`SSL certificate database initialized at: ${sslDbPath}`);
Expand Down
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