Cyber Posture

CVE-2025-27915

MediumCISA KEVActive ExploitationPublic PoC

Published: 12 March 2025

Published
12 March 2025
Modified
04 November 2025
KEV Added
07 October 2025
Patch
—
CVSS Score 5.4 CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
EPSS Score 0.2605 96.3th percentile
Risk Priority 46 60% EPSS · 20% KEV · 20% CVSS

Description

Adversaries may employ various time-based methods to evade detection and analysis.

Security Summary

CVE-2025-27915 is a stored cross-site scripting (XSS) vulnerability, classified under CWE-79, affecting Zimbra Collaboration Suite (ZCS) versions 9.0, 10.0, and 10.1, specifically in the Classic Web Client. The flaw arises from insufficient sanitization of HTML content within ICS files attached to or embedded in emails. A malicious ICS entry can include JavaScript that executes via an ontoggle event within a <details> tag when the email is viewed. The vulnerability has a CVSS v3.1 base score of 5.4 (AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N).

An attacker with low privileges, such as a ZCS user account, can exploit this by sending an email containing the malicious ICS to a target victim. When the victim opens and views the email in the Classic Web Client, the embedded JavaScript executes in the context of the victim's authenticated browser session. This enables arbitrary code execution, allowing the attacker to perform actions like configuring email filters to redirect messages to an attacker-controlled address, leading to unauthorized account actions, email redirection, and potential data exfiltration.

Zimbra advisories document fixes in patches for affected versions: ZCS 10.0.13, 10.1.5, and 9.0.0 Patch 44 (P44). Administrators should apply these updates to mitigate the issue, as detailed in the Zimbra Security Center and release notes.

The vulnerability has seen real-world exploitation as a zero-day ICS attack, as reported in external analysis.

Details

CWE(s)
CWE-79
KEV Date Added
07 October 2025

Affected Products

synacor
zimbra collaboration suite
9.0.0 · 10.0.0 — 10.0.13 · 10.1.0 — 10.1.5

MITRE ATT&CK Enterprise Techniques

T1027 Obfuscated Files or Information Stealth
Adversaries may attempt to make an executable or file difficult to discover or analyze by encrypting, encoding, or otherwise obfuscating its contents on the system or in transit.
attack.mitre.org →
T1041 Exfiltration Over C2 Channel Exfiltration
Adversaries may steal data by exfiltrating it over an existing command and control channel.
attack.mitre.org →
T1059.007 JavaScript Execution
Adversaries may abuse various implementations of JavaScript for execution.
attack.mitre.org →
T1114.001 Local Email Collection Collection
Adversaries may target user email on local systems to collect sensitive information.
attack.mitre.org →
T1114.003 Email Forwarding Rule Collection
Adversaries may setup email forwarding rules to collect sensitive information.
attack.mitre.org →
T1480 Execution Guardrails Stealth
Adversaries may use execution guardrails to constrain execution or actions based on adversary supplied and environment specific conditions that are expected to be present on the target.
attack.mitre.org →
T1497.002 User Activity Based Checks Stealth
Adversaries may employ various user activity checks to detect and avoid virtualization and analysis environments.
attack.mitre.org →
T1564.003 Hidden Window Stealth
Adversaries may use hidden windows to conceal malicious activity from the plain sight of users.
attack.mitre.org →
T1566.001 Spearphishing Attachment Initial Access
Adversaries may send spearphishing emails with a malicious attachment in an attempt to gain access to victim systems.
attack.mitre.org →
T1678 Delay Execution Stealth
Adversaries may employ various time-based methods to evade detection and analysis.
attack.mitre.org →
Why these techniques?

Stored XSS via malicious ICS in email enables JavaScript execution for obfuscated payload delivery through spearphishing attachment, email collection and forwarding rules, data exfiltration over C2, UI hiding, execution delays/guardrails, and user activity checks.

References