CVE-2025-27915: Synacor exploited

Advisory generated from the CVE record, CISA, Exploit Observer and VEDAS: what it is, whether it is exploited, who is affected, and how to fix and detect it.

What it is

An issue was discovered in Zimbra Collaboration (ZCS) 9.0 and 10.0 and 10.1. A stored cross-site scripting (XSS) vulnerability exists in the Classic Web Client due to insufficient sanitization of HTML content in ICS files. When a user views an e-mail message containing a malicious ICS entry, its embedded JavaScript executes via an ontoggle event inside a <details> tag. This allows an attacker to run arbitrary JavaScript within the victim’s session, potentially leading to unauthorized actions such as setting e-mail filters to redirect messages to an attacker-controlled address. As a result, an attacker can perform unauthorized actions on the victim’s account, including e-mail redirection and data exfiltration.

Description quoted from the CVE record (assigned by mitre, published 2025-03-12).

Weakness: CWE-79 Improper Neutralization of Input During Web Page Generation (‘Cross-site Scripting’)

How it can be exploited

Exploitable over the network with low attack complexity needing low privileges and a user must take an action. Impact: confidentiality low, integrity low, availability none. CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

CISA assessment (SSVC): CISA assesses exploitation as active. Automatable: no. Technical impact: total.

On CISA KEV since: 2025-10-07
US federal deadline: 2025-10-28
Ransomware use: Not known

Public exploit evidence (Exploit Observer)

Also known as: BDU:2025-12561, CNNVD-202503-1502, EUVD-2025-7823, GHSA-5rg8-g76j-7fw7

VEDAS cluster: VEDAS:FLIRTFIRE

Exploit Observer links 6 pieces of public exploit code or detection modules that name this CVE or one of its aliases.

Exploit code and modules (6)

Code that names this CVE. A repository can be a working exploit, a scanner, a fake or malware; read it before running anything.

Research and write-ups (2)

Research or write-up: https://ptsecurity.com/research/trending-vulnerabilities/CVE-2025-27915
Research or write-up: https://www.rapid7.com/db/vulnerabilities/zimbra-collaboration-cve-2025-27915

Vulnerability databases and vendor advisories (7)

Catalogue entries, not exploit evidence.

Vulnerability database or vendor advisory: https://access.redhat.com/security/cve/cve-2025-27915
Vulnerability database or vendor advisory: https://euvd.enisa.europa.eu/enisa/EUVD-2025-7823
Vulnerability database or vendor advisory: https://github.com/advisories/GHSA-5rg8-g76j-7fw7
Vulnerability database or vendor advisory: https://nvd.nist.gov/vuln/detail/CVE-2025-27915
Vulnerability database or vendor advisory: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-27915
Vulnerability database or vendor advisory: https://www.cnnvd.org.cn/home/globalSearch?keyword=CNNVD-202503-1502
Vulnerability database or vendor advisory: https://www.tenable.com/cve/CVE-2025-27915

41 more references returned by Exploit Observer did not name this CVE or an alias, so they are left out.

VEDAS data as of 2026-11-01T17:12 UTC; fetched 2026-11-02.

Live scores

EPSS: 0.041
some chance of attack soon
VEDAS: 0.989
strong exploit evidence
On CISA KEV: Yes, since 2025-10-07
Detection rule: Nuclei · Suricata

EPSS (chance of attack)

VEDAS (exploit evidence)

Thin horizontal line: the “likely” (EPSS 0.10) or “strong” (VEDAS 0.90) threshold. Shaded “no data” areas are periods when cve-scores did not publish. The vertical line is the day CISA added it to its exploited list.

Who is affected

Product	Affected	Not affected
Not stated	version n/a	Not stated

Version ranges exactly as the CVE record states them. “Before X” means X is the first fixed version.

How to fix it

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.

Vendor guidance:

How to detect it

Nuclei template (active check)

Zimbra - Cross-Site Scripting
An issue was discovered in Zimbra Collaboration (ZCS) 9.0 and 10.0 and 10.1. A stored cross-site scripting (XSS) vulnerability exists in the Classic Web Client due to insufficient sanitization of HTML content in ICS files.

Name and description quoted from the template, written by VEDAS.

The template sends 1 request (GET /js/zimbraMail/share/model/ZmSettings.js); it decides using dsl, regex, word matchers. Severity in the template: medium. Marked as not yet verified against a live vulnerable target.

Run it against a host you own or are authorised to test:

bash

nuclei -u https://your-host -t CVE-2025-27915.yaml

Show the template (52 lines)

yaml

id: CVE-2025-27915

info:
  name: "Zimbra - Cross-Site Scripting"
  author: vedas-arpsyndicate
  severity: medium
  description: |
    An issue was discovered in Zimbra Collaboration (ZCS) 9.0 and 10.0 and 10.1. A stored cross-site scripting
    (XSS) vulnerability exists in the Classic Web Client due to insufficient sanitization of HTML content in ICS
    files.
  reference:
    - https://www.exploit.observer/?keyword=CVE-2025-27915&match=exact
    - https://subdomain.center/?engine=ammonites&keyword=zimbra&match=exact
  classification:
    cvss-metrics: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
    cvss-score: 5.4
    cve-id: CVE-2025-27915
    cwe-id: CWE-79
  metadata:
    verified: false
  tags: cve,cve2025,zimbra,xss,ics,kev,vkev,vuln
http:
  - method: GET
    path:
      - "{{BaseURL}}/js/zimbraMail/share/model/ZmSettings.js"

    matchers-condition: and
    matchers:
      - type: word
        part: body
        words:
          - "Zimbra Collaboration Suite"

      - type: word
        part: header
        words:
          - "application/x-javascript"

      - type: dsl
        dsl:
          - compare_versions(version, '9.0.0')
          - compare_versions(version, '>= 10.0.0', '< 10.0.13')
          - compare_versions(version, '>= 10.1.0', '< 10.1.5')
        condition: or

    extractors:
      - type: regex
        part: body
        name: version
        group: 1
        regex:
          - CLIENT_VERSION\",\s+{type:ZmSetting\.T_CONFIG, defaultValue:"([0-9.]+)_([A-Z_0-9]+)"\}

CVE-2025-27915.yaml on GitHub

Suricata rules (network detection)

1 rule that alert on traffic matching this exploit: VEDAS CVE-2025-27915 Zimbra - Cross-Site Scripting. Add them to your Suricata rule set and reload.

Show the rules

suricata

alert http $EXTERNAL_NET any -> $HTTP_SERVERS $HTTP_PORTS (msg:"VEDAS CVE-2025-27915 Zimbra - Cross-Site Scripting"; flow:established,to_server; http.method; content:"GET"; http.uri; content:"index.php"; nocase; fast_pattern; content:"<script"; nocase; classtype:web-application-attack; reference:cve,CVE-2025-27915; reference:url,https://www.exploit.observer/?keyword=CVE-2025-27915&match=exact; reference:url,https://subdomain.center/?engine=ammonites&keyword=zimbra&match=exact; sid:1002822; rev:2;)

CVE-2025-27915.rules on GitHub

References

Other references

Other databases

Where this comes from

This advisory is generated automatically by VEDAS from: CVE.org record, CISA KEV, cve-scores (EPSS and VEDAS), Exploit Observer, vedas-signatures. Text in quotes is reproduced from the source; everything else is a fixed template filled with source fields. Nothing here is written by a language model. Check the vendor advisory before acting, and read how VEDAS and Exploit Observer work, and their limits.