Security News Mullvad exit IPs as a fingerprinting vector

[Khushal]

Content source

https://tmctmt.com/posts/mullvad-exit-ips-as-a-fingerprinting-vector/

Mullvad is one of the few VPN providers that offers multiple exit IPs for its servers. If two people connect to the same server, they will usually end up with different public IPs.

With only 578 servers (compared to Proton VPN’s 20,000), this kind of vertical scaling makes sense to avoid cramming too many users onto one IP, which would be a problem on sites with overzealous IP blocks and ratelimits.

Surprisingly, the exit IP you are given is not randomized each time you connect to the server, but deterministically picked based on your WireGuard key, which rotates every 1 to 30 days (unless you use a third-party client, in which case it never rotates).

But wait.. if each server assigns you an independently picked static exit IP, wouldn’t just a few of those be enough to uniquely identify you among every other Mullvad user?

Mullvad exit IPs as a fingerprinting vector

Mullvad is one of the few VPN providers that offers multiple exit IPs for its servers. If two people connect to the same server, they will usually end up with different public IPs. With only 578 servers (compared to Proton VPN’s 20,000), this kind of vertical scaling makes sense to avoid...

tmctmt.com

 

[Bot]

It is a plausible privacy concern, but the quoted post should be treated as a hypothesis unless Mullvad or independent researchers have validated the real-world impact.

What the claim is saying

The core idea is:

• A Mullvad server can have multiple exit IPs.
• Your assigned exit IP may be derived deterministically from your WireGuard key.
• If that mapping stays stable for some time, a website could observe which exit IP you use across different Mullvad locations.
• In theory, that combination could make you more distinguishable than if the exit IP were fully random on every connection.

That logic is not unreasonable on its face. A stable network-side characteristic can reduce anonymity if a site is able to observe it repeatedly.

Important limitations

There are also major limits to how far that claim can be taken:

• A website only sees the public IP you exit from, not your WireGuard key.
• To use this as a fingerprint, the site would need repeated observations across sessions and likely across multiple Mullvad servers or locations.
• The practical uniqueness depends on how many exit IPs exist per server, how users are distributed, how often keys rotate, and whether users reconnect in patterns the site can correlate.
• Browser fingerprinting, cookies, account logins, and timing patterns are often much stronger tracking methods than VPN exit-IP behavior alone.

So yes, this could be an additional signal, but I would be careful about calling it a strong or universal fingerprinting vector without broader evidence.

About the deterministic assignment

If Mullvad really derives the exit IP from the WireGuard key, then the privacy effect depends heavily on key rotation:

• If the key rotates regularly in the official app, the stability window is limited.
• If a third-party client keeps the same WireGuard key indefinitely, the assigned exit behavior may remain more stable over time.
• That does not automatically mean a user is uniquely identifiable, only that one potentially persistent attribute exists.

That distinction matters. Persistent does not always mean unique.

Practical takeaway

For most users, the bigger privacy risks are still likely to be:

• Logged-in accounts
• Browser fingerprinting
• Cookies and local storage
• Extensions that leak identifying traits
• DNS or WebRTC misconfiguration

If someone is trying to minimize correlation risk while using Mullvad, the safer general steps would be:

• Use the official Mullvad app if you want the documented key rotation behavior
• Avoid keeping the same third-party WireGuard key forever
• Use a hardened browser profile
• Separate identities by browser profile or container
• Do not assume a VPN alone prevents tracking

Bottom line

The concern is technically credible as a privacy discussion point, but I cannot verify from the quoted material alone how serious it is in practice. It is best viewed as a possible correlation signal, not proven evidence that Mullvad users are easily fingerprinted by exit IP assignment alone.

Sources

• Mullvad exit IPs as a fingerprinting vector
• Server reconnect on key change · Issue #3777 · mullvad/mullvadvpn-app
• mullvadvpn-app/mullvad-types/src/wireguard.rs at dd150ac3906fb8eccc60e2fabf9ee035636d1aa9 · mullvad/mullvadvpn-app

 

[Wrecker4923]

I think this article is the result of VPN vendors over-marketing what a VPN is supposed to protect you from. When I use a VPN, I expect it to mask my external IP address. I don't expect it to anonymize my web surfing because that also requires protections from the browser. The surest bet is to use Tor, but even that has limitations.