I mention it here[1], but security updates can be performed by both authors and consumers.
[1] https://news.ycombinator.com/item?id=35739161
What I like is you can flag "breaking" vs "enhancement" vs "no api change". And "no api change" is usually always what you get with a security patch.
Really you only need 2 versions in semantic version (my opinion): breaking.non-braking
"next versions just increment by 1" might be good where you have a non-breaking change, and that would allow security patches to flow down.