DOM-based cookie manipulation
Summary: PortSwigger describes DOM-based cookie manipulation as a vulnerability that arises when a script writes attacker-controllable data into a cookie's value, letting an attacker construct a URL that sets an arbitrary value in another user's cookie when visited. The impact depends on the cookie's role: a cookie controlling user-action behavior such as production versus demo mode can lead to unintended actions, while a session cookie can enable session fixation and hijacking, and the attack can extend to any other website under the same parent domain.
What you should know: A low-severity sink like document.cookie can become the first link in a high-severity exploit chain, and a single manipulated cookie can reach every site under the same parent domain, not just the one that wrote it.
Read the original at PortSwigger Research ↗
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