# The CSS rule that made a hidden field visible

DevFeed: [The CSS rule that made a hidden field visible](<https://devfeed.tech/articles/the-css-rule-that-made-a-hidden-field-visible-36155.md>)

Original publisher: [Read original article](<https://as215248.net/notes/the-hidden-attribute-lied/>)

Author: Bastiaan Brink

Published: 2026-08-02T00:00:00Z

Content type: opinion

Language: en

Sources: [AS215248 - Notes](<https://devfeed.tech/sources/as215248-notes.md>)

Topics: [CSS](<https://devfeed.tech/topics/css.md>), [Web Development](<https://devfeed.tech/topics/web-development.md>), [client](<https://devfeed.tech/topics/client.md>), [servers](<https://devfeed.tech/topics/servers.md>)

Tags: [client](<https://devfeed.tech/tags/client.md>), [css](<https://devfeed.tech/tags/css.md>), [debugging](<https://devfeed.tech/tags/debugging.md>), [hidden](<https://devfeed.tech/tags/hidden.md>), [meta](<https://devfeed.tech/tags/meta.md>), [server](<https://devfeed.tech/tags/server.md>)

## AI overview

The article explains how a CSS rule overrode the HTML hidden attribute, making an operator-only field visible on a peering portal. The field was not a security leak because the server enforced an identity-based allowlist and returned 403 responses for unauthorized requests.

## Source excerpt

Every visitor could see an internal field on the peering portal. Not a leak -- the server never trusted it -- but a good reminder about how `hidden` actually works.