Critical Vulnerability in Swedish BankID Exposes User Data

This story was originally published on HackerNoon at: https://hackernoon.com/critical-vulnerability-in-swedish-bankid-exposes-user-data.
A common misconfiguration found in services integrating BankID, allows attackers to take over victim's accounts exploiting a Session Fixation bug
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When a service uses BankID to authenticate their users it is common for them to incorrectly implement some security features of the protocol which leaves them exposed to a Session Fixation CWE-384 vulnerability which can be used by an attacker to hijack a victim’s session on that service. Depending on the amount of access the attacker has after exploiting this vulnerability, the severity of such security flaw ranges between High and Critical