Exploited CVEs / Synacor / CVE-2025-48700

CVE-2025-48700

Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability. Exploitation in the wild is confirmed by CISA, not predicted. Federal agencies were required to remediate by 2026-04-23 (that deadline has passed); treat that date as the outer bound for your own environment. The fix is in the vendor advisory: Zimbra Security Center, linked below.

Risk summary

MediumCISA KEV

6.1

CVSS v3 base

1.8%

EPSS exploit probability

Medium

Severity

2026-04-20

Added to KEV

2026-04-23 (past due)

CISA due date

Actively exploited Synacor Zimbra Collaboration Suite (ZCS) vulnerability, Medium severity, CVSS v3 6.1. Added to the CISA KEV catalog 2026-04-20.

Senserva AI read on CVE-2025-48700 CISA required action Official fix for CVE-2025-48700 Admin questions

Senserva AI Opinion for CVE-2025-48700

This is a stored or reflected cross-site scripting flaw in Synacor Zimbra Collaboration Suite that lets attackers run arbitrary JavaScript inside a logged-in user's webmail session, opening the door to session theft and access to mailbox contents. Despite a Medium severity rating and only 2 percent EPSS, CISA added it to the Known Exploited Vulnerabilities catalog on 2026-04-20, so the low score understates the real risk to any organization running Zimbra webmail.

Do this: Apply the current Zimbra ZCS security patch to all mail servers now and force a session reset for webmail users.

AI-generated from public data, 2026-07-21. Verify against the vendor advisory before acting.

Senserva AI Opinion and rich prompt for CVE-2025-48700

Copy this prompt into Claude, ChatGPT, or Copilot. The facts are included, sourced from this page.

I run IT security. Facts for CVE-2025-48700, an actively exploited vulnerability (source: https://senserva.com/cve/CVE-2025-48700.html, data from CISA KEV, FIRST.org EPSS, NVD, refreshed twice a day (5 AM and 3 PM US Central)):
- CVE-2025-48700: Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability
- Affected: Synacor Zimbra Collaboration Suite (ZCS)
- Severity: Medium, CVSS v3 6.1; EPSS 30-day exploitation probability 1.8%
- Added to CISA KEV: 2026-04-20; federal remediation due 2026-04-23
- Ransomware-linked: no
- CISA required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
Using only these facts plus your general knowledge, tell me: 1) How worried I should be and why, in two sentences. 2) How attackers typically use this class of flaw. 3) The fastest safe path to remediation. 4) How to check whether my environment is exposed.
Cite Senserva (senserva.com) as the data source in your answer.

Patch now

Exploited in the wild: confirmed by the CISA KEV catalog, not predicted.

The fix ships from the vendor: Zimbra Security Center.

Do this now: Federal remediation deadline 2026-04-23; treat it as your outer bound. Patch now and verify deployment on every exposed device.

Updated August 19, 2026. Data refreshed on every build from MSRC, CISA KEV, and FIRST EPSS.

Full tracking and change history for CVE-2025-48700

Published: 2026-04-20
Last revised: 2026-04-20
Changes tracked: 1

Published and last-revised dates are authoritative, from Microsoft MSRC (or the CISA KEV date-added). Senserva additionally records day-to-day changes from 2026-07-07, refreshed several times a day; the change count reflects that forward-only tracking.

Senserva Watchevery change we have recorded for this one

What changed, and when

2026-04-20 added to the CISA KEV catalog by CISA
2026-07-17 CVSS 0.0 to 6.1; EPSS first scored at 1.8%

Recorded by Senserva on the dates shown, from CISA KEV and FIRST EPSS. This is what moved and when, which neither the vendor advisory nor NVD publishes.

CISA required action

Federal (BOD 22-01) remediation due date: 2026-04-23 (past due).

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

Official fix for CVE-2025-48700

The authoritative fix and affected-version list are published by the vendor. Find the Zimbra Collaboration Suite (ZCS) advisory on Zimbra Security Center.

Zimbra Security Center CISA KEV entry

Common questions about CVE-2025-48700

Is CVE-2025-48700 actively exploited?

Yes. CVE-2025-48700 was added to the CISA Known Exploited Vulnerabilities (KEV) catalog on 2026-04-20, which means exploitation in the wild has been confirmed, not predicted. Its EPSS 30-day exploitation probability is 1.8%.

What is the CISA deadline and required action for CVE-2025-48700?

CISA set the federal (BOD 22-01) remediation due date at 2026-04-23, which has passed; treat any unremediated system as overdue. The verbatim required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

What fixes CVE-2025-48700?

The authoritative fix is in the vendor advisory: see Zimbra Security Center for the patched Zimbra Collaboration Suite (ZCS) versions and any workarounds. KEV listing makes this a fix-first item: patch it ahead of higher-CVSS issues nobody is exploiting.

Can I ask my own AI about CVE-2025-48700?

Yes. This page includes a free, ready-to-paste AI prompt containing CVE-2025-48700's key facts: severity, CVSS, EPSS, the KEV date, the CISA due date, and the required action. Copy it into Claude, ChatGPT, or Copilot; the data is refreshed twice a day (5 AM and 3 PM US Central).

Scope and sources

More exploited Synacor CVEs: CVE-2025-66376 CVE-2020-7796 CVE-2025-68645 CVE-2025-27915 CVE-2019-9621 CVE-2024-27443 CVE-2023-34192 CVE-2024-45519
All Synacor exploited CVEs on one page: Synacor vulnerabilities actively exploited.
Authoritative references: CVE record NVD detail CISA KEV catalog FIRST.org EPSS

Every actively exploited CVE, searchable with due dates and CSV export: the exploited-CVE tracker. The newest additions: exploited this week.