SquirrelMail is a legacy PHP webmail application. It can still be operated securely in constrained environments, but requires strict web/PHP hardening and careful patch tracking.
- Monitor the SquirrelMail security page for new CVEs.
- Apply available patches or maintained package updates quickly.
- Validate HTML message rendering and attachment handling after updates.
- Remove deprecated plugins that are no longer maintained.
¶ 2) Harden PHP session and runtime settings
- Use cookie-based sessions only; disable URL session IDs.
- Set secure session storage path not shared with other applications.
- Disable dangerous PHP functions where possible.
- Keep PHP current and disable verbose error output in production.
¶ 3) Protect webmail endpoint and plugin surface
- Enforce HTTPS and strict security headers at reverse proxy.
- Restrict access by network policy for internal deployments.
- Disable unused SquirrelMail plugins and themes.
- Keep attachment/temp paths outside web root where possible.
- Force TLS for IMAP/SMTP with certificate validation.
- Restrict backend mail host access to trusted network paths.
- Use least-privilege service credentials for any backend integrations.
- Rotate credentials and audit login failures.
¶ Verification commands
grep -R "session\|cookie\|imap\|smtp" /etc/squirrelmail /var/www/squirrelmail/config 2>/dev/null | head
php -i | grep -E "session.save_path|session.use_only_cookies|display_errors"
sudo ss -tulpn | grep -E ':443|:993|:465|:587'
- SquirrelMail security page: https://www.squirrelmail.org/security/
- SquirrelMail project site: https://www.squirrelmail.org/