The `@quasar/ssl-certificate` development utility caches a combined PEM containing a generated private key and certificate without explicitly restricting its filesystem permissions. On systems with a typical process umask, the PEM can be readable by other local users. A local attacker with filesystem access could copy and reuse the private key to impersonate a development TLS endpoint in an environment that trusts the certificate.

The generated certificate was also unnecessarily CA-capable and included broad key usages beyond its localhost HTTPS purpose. Its IPv6 loopback entry was encoded as a DNS name rather than an IP subject alternative name.

The remediation writes and repairs the cached PEM with owner-only permissions on supported platforms, generates a non-CA server-auth leaf certificate with constrained key usage, corrects the IPv6 loopback SAN, and bases cache expiry on content modification time so permission metadata changes cannot extend the certificate lifetime. This issue does not expose the key remotely by itself; exploitation requires another local user to be able to read the cached PEM file.