Since Chromium 148, Math.tanh is now fingerprintable to link underlying OS

We noticed Chromium Math.tanh since v148 returned a different result, so we dig it - it's now a fingerprintable surface to retrieve the OS Chromium run on

I guess that's one more good reason to push for correctly rounded transcendental functions. I recently learned that they're basically solved now. [1]

[1] https://arith2026.org/program.html (2nd keynote)

Tangential, but wow do they really register a new domain for each year and renew it in perpetuity?

> One tanh call on the right input is a per-OS signature. Claim macOS, return Linux math bits, and you have contradicted your own User-Agent.

They (or rather the LLM that wrote this) missed that this is possibly fingerprintable to browser version range, which is slightly more interesting. Most users aren't spoofing their user agent headers to be a different operating system. Most fingerprinting solutions aren't trying to infer your operating system, they only care about semi-unique things that show up.

It's an interesting finding. I wish they had taken some time to have a real person write it up. This is too heavily LLM written to ignore.

Kind of a smart move by this company: write up an AI analysis of all fingerprinting techniques in hopes they get fixed after outrage so their scraping company can make more money. If it weren't for companies like this, fingerprinting wouldn't be so ubiquitous and the internet would be a better place in general.

I prefer articles like this coming from the other side of the battle (fingerprint.js and friends) because at least their motives are clear.