That UI Bug with Missing Data is a Security Issue

| python | projects | security |

This is (sometimes) a development blog, so I am going to write about some failed development of mine since writing about success is much less interesting. You know that UI bug that someone added to your GitHub Issues where there is some missing data? You know the one, it only happens in production, all of your tests pass, and you marked it as a low priority. Yeah, that one. It’s probably a security bug and you should look into it right away. At least, that is the lesson I taught myself yet again when I began to research this bug.

before

<a id="shared_note.id)" href=""{{">
{{current_user.notes.filter_by(id=shared_note.id).first().title}}
</a>

after

<a href="{{ url_for('main.note', id=shared_note.note_id) }}">
{{current_user.notes.filter_by(id=shared_note.note_id).first().title}}
</a>

The difference is very subtle, but the key issue here is shared_note.id vs shared_note.note_id; I released a feature a few weeks ago that showed you all of the notes that you have shared. Locally everything worked fine, but I noticed later on, once it was in production, that the note title was not showing up. This is, of course, due to the fact that rather than showing the title of the note with the ID shared_note.note_id (the foreign key linking to the note) I was showing the title for the note with the primary key of shared_note.id. The reason why this is a security issue is because this allows someone to share a bunch of notes and start seeing the titles for notes that they do not own. The reason why this worked locally is because I am only testing with a single user, with a single notebook, with a single note, and with a single shared note. This means that in this specific case all of the Primary Keys and Foreign Keys are usually “1” so everything just happens to work.

Key Takeaways

Thank you for reading! Share your thoughts with me on bluesky, mastodon, or via email.

Check out some more stuff to read down below.

Most popular posts this month

Recent Favorite Blog Posts

This is a collection of the last 8 posts that I bookmarked.

Articles from blogs I follow around the net

Issue 91 – GDP on the blockchain

The regulator set to take on primary crypto oversight is down to a single Commissioner, and new pro-crypto PACs focus on installing more Republicans in the midterms

via Citation Needed August 27, 2025

V&A East Storehouse and Operation Mincemeat in London

We were back in London for a few days and yesterday had a day of culture. First up: the brand new V&A East Storehouse museum in the Queen Elizabeth Olympic Park near Stratford, which opened on May 31st this year. This is a delightful new format for a mu…

via Simon Willison's Weblog: Entries August 27, 2025

St Jude 2025

St Jude 2025

via Robb Knight • Posts • Atom Feed August 27, 2025

Generated by openring