CVE-2026-50053: Zimbra Collaboration Suite RestFilter Request Attribute Override via Unauthenticated URL Parameters
A request attribute override vulnerability in Zimbra Collaboration Suite (ZCS) allows unauthenticated requests to /h/ to populate servlet attributes intended for trusted internal dispatch. RestFilter copies URL parameters specifying an authentication token, target account, target item and dispatch state into the request attributes consumed by the Classic Web Client. Combined with CVE-2026-10632 on ZCS 10.1.16, this allows an attacker to supply their own valid token and document identifiers and execute JavaScript in another user's signed-in browser session. ZCS 10.1.17 blocks that XSS chain by changing the document renderer, but retains the request attribute override.
Affected Software
Event History
Frequently Asked Questions
What does an attacker need to exploit the documented cross-site scripting chain?
The attacker needs to combine this issue with CVE-2026-10632 and supply their own valid authentication token and document identifiers. The resulting JavaScript execution occurs in another user's signed-in Classic Web Client browser session.
Which ZCS versions are known to be affected by the XSS chain?
The described chain is confirmed on ZCS 10.1.16. ZCS 10.1.17 changes the document renderer to block that XSS chain, although the request attribute override itself remains.
What should teams do if they are concerned about the XSS impact?
Move to ZCS 10.1.17 or later where the document renderer change blocks the described chain. Do not treat that change as removing the underlying request attribute override behavior.