Improves input validation, path handling robustness, and environment variable handling across the electron-updater auto-update flow. Changes span LinuxUpdater, BaseUpdater, AppUpdater, and AppImageUpdater.

Changes

packages/electron-updater/src/LinuxUpdater.ts

1. ELECTRON_BUILDER_LINUX_PACKAGE_MANAGER env var — stricter validation (detectPackageManager)

• Added SAFE_PM_REGEX = /^[a-zA-Z0-9_-]+$/ — validates that the override value is a well-formed command name before use. Values that don't match log a warning and fall through to automatic detection.
• Added hasCommand(pmOverride) check — verifies the specified binary is present on the system before using it. If not found, logs a warning and falls through to automatic detection.
• Both checks are non-fatal: invalid or unavailable overrides degrade gracefully to the standard PM priority list rather than breaking the update flow.

2. Installer path handling (installerPath getter)

• Extended the set of characters that are backslash-escaped for POSIX shell contexts: previously only \ and space were handled; now also covers `, $, !, ", ;, |, &, (, ), <, >.
• Strips \n / \r characters from paths entirely.

3. App name handling in sudo dialog (runCommandWithSudoIfNeeded)

• Strips shell-meaningful characters from this.app.name before embedding it in the sudo dialog comment string, ensuring the comment is well-formed regardless of what the app name contains.

packages/electron-updater/src/BaseUpdater.ts

4. PATH normalization in spawnSyncLog

• Extracted sanitizeEnvPath(envPath: string): string — filters the inherited PATH to retain only absolute-path entries before passing it to spawnSync.
• Added import * as path from "path" (previously absent).

packages/electron-updater/src/AppUpdater.ts

5. Consistent cache filename derivation (executeDownload → getCacheUpdateFileName)

• The fallback branch (used when the URL does not end with the expected file extension, e.g. /latest-style redirect URLs) now applies path.basename(...) to the URL string, matching the treatment already applied in the primary branch.

packages/electron-updater/src/AppImageUpdater.ts

6. APPIMAGE env var — path validation (doInstall)

• Added path.isAbsolute and null-byte checks on process.env["APPIMAGE"] before use. Produces a clear ERR_UPDATER_OLD_FILE_NOT_FOUND error if the value is not a valid absolute path.