What are KDF parameters in OpenSSL command-line utility for `enc`?
OpenSSL uses EVP_BytesToKey, an algorithm proprietary to OpenSSL, with a salt and an iteration count set to 1. The algorithm is secure; the iteration count of 1 of course is not secure (for passwords with an average strength). Implementations for other languages/runtimes can be found by searching for it by name.

This page (on nabble.com) explains a bit about accessing PBKDF2 from the command line. It also shows that OpenSSL CLI isn't always taken that seriously; OpenSSL is mainly a cryptographic library that can also be used from the command line.

It is possible to find code to include the iteration count in the CLI in the answers to this question on the security site (not reviewed by me). That code is however specific to private keys encrypted using the PKCS#8 standard.

It could well be that PGP is more suited for end-to-end password encryption (I haven't reviewed it for a while). It was certainly more specifically created for it.