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The X11 Security extension from the 1990s

blog - git - desktop - images - contact 2025-08-02 It's widely known that X11 has a problem with, for example, keyloggers. The issue is not that keyloggers are possible through security holes -- but keyloggers are trivial on X11, as they are part of normal operation and don't require exploits.

The thing is that it's immediately clear that this extension -- in its current state-- is not the answer to "X11 is insecure": You only have two classes, trusted and untrusted. If you run programs "the traditional way" (i.e., full access to the filesystem and network), then an attacker can do all kinds of things and X11 keylogging is just one of a million concerns. If anything, this extension could have been the foundation for or a first step towards client isolation on X11 -- if it had been widely adopted decades ago, when it originally came out.

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