TL;DR
A researcher discovered that Mullvad VPN’s exit IPs are assigned based on a deterministic algorithm linked to user keys, potentially allowing user identification. This challenges assumptions about VPN anonymity and raises privacy issues.
A security researcher has revealed that Mullvad VPN’s exit IP addresses are assigned deterministically based on user keys, which could allow for user identification and compromise privacy. This finding challenges the common assumption that Mullvad offers high anonymity through randomized IPs, raising concerns among privacy advocates and users.
The researcher conducted a night-long test, repeatedly changing their WireGuard public key and fetching exit IPs from nine Mullvad servers. Despite the enormous pool of over 8.2 trillion possible IP combinations, the test showed that users are assigned only 284 specific IP combinations, indicating a predictable pattern.
The pattern was traced to a seed-based pseudorandom number generator (RNG) used by Mullvad, likely implemented in Rust, which deterministically selects exit IPs based on user keys. This means that users sharing similar keys or patterns could potentially be identified by analyzing their assigned IPs, especially if the same seed or algorithm is used across servers.
Why It Matters
This discovery raises privacy concerns for Mullvad users, as the deterministic IP assignment could enable correlation of user activity and identification, undermining the VPN’s reputation for anonymity. It also prompts a reevaluation of how VPN providers implement IP rotation and randomness, emphasizing the importance of truly unpredictable assignment methods for preserving user privacy.
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Background
Mullvad is known for offering multiple exit IPs per server, with IPs assigned based on user keys rather than randomization. Unlike larger VPN providers like Proton VPN, Mullvad’s approach was believed to enhance privacy through IP variability. The recent analysis, however, shows that the assignment process is predictable, which could compromise user anonymity. The use of deterministic algorithms in cryptographic contexts is common, but in this case, it appears to reduce the effective entropy of user IPs.
“The exit IPs are not randomly assigned but are deterministically picked based on user keys, which can potentially be used to identify users.”
— Researcher
“If the IPs are predictable, it undermines one of the key privacy features of Mullvad, which is supposed to provide high anonymity.”
— VPN privacy expert
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What Remains Unclear
It remains unclear whether Mullvad intentionally uses this deterministic method or if it is an unintended consequence of their implementation. The exact details of their seed generation and whether this pattern applies uniformly across all servers are still being investigated. Additionally, the practical risk of user de-anonymization in real-world scenarios needs further assessment.
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What’s Next
Further analysis is expected to clarify whether Mullvad will modify their IP assignment algorithms. Users and security researchers will likely scrutinize the VPN’s privacy guarantees, and independent audits may be conducted to assess the potential for user identification. Monitoring updates from Mullvad regarding this issue is anticipated.
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Key Questions
Can Mullvad users be identified through their exit IPs?
Based on current findings, it is possible in theory to correlate user activity with specific IPs, especially if the IP assignment pattern is known. The actual risk depends on how the algorithm is used in practice and whether additional data is available to an attacker.
Did Mullvad admit to using a deterministic IP assignment method?
There has been no official statement from Mullvad confirming or denying the use of such an algorithm. The analysis is based on observed patterns and reverse engineering efforts.
Does this mean Mullvad is no longer private?
This discovery raises concerns about the level of privacy Mullvad provides. While it does not necessarily mean the VPN is insecure, it suggests that its privacy guarantees may not be as strong as previously believed, especially against sophisticated adversaries.
Will Mullvad change their IP assignment process?
It is unclear. The company has not issued a public statement, but given the implications, they may consider modifying their system to improve unpredictability and user privacy.
