Zimbra Collaboration Suite RestFilter Request Attribute Override via Unauthenticated URL Parameters

published 2026-10-23 17 d ago modified 2026-11-02 6 d ago also EUVD-2026-108962

cvss: 8.7; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.3%; EPSS 0.3% chance of exploitation in 30 days, percentile 21%
public exploits: 0; none known

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.

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: total
Assessed: 11 d ago (2026-10-28)

Exploit prediction

0.29% chance of exploitation in the next 30 days, higher than 21% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	8.7	CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N
NVD	3.1	5.4	CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

Affected products

Zimbra Zimbra Collaboration Suite

Classification

Weakness

CWE-642 External Control of Critical State Data

References

wiki.zimbra.com /wiki/Zimbra_Security_Advisories
vendor-advisory
rapid7.com /blog/post/ve-breaking-zimbra-identity-boundaries-part-1/
related, not-applicable

Sources

CVE List CVE-2026-50053
NVD CVE-2026-50053

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Summary