Synacor Zimbra Collaboration Suite (ZCS) PHP Remote File Inclusion Vulnerability

CheckOps priority index

7.4/10 Patch within 7 days

Severity8.8

Probability4.9

Exploitation4/5

Severity = CVSS. Probability = EPSS (FIRST). Exploitation = public signals: KEV, EUVD, ransomware, EPSS above 10 %, no account required.

EPSS · today 48.9% higher than 98.9% of CVEs

CVSS 3.1 8.8 AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:

Exploited for 285 days 22 Jan 2026

CISA due date 12 Feb 2026 for US federal agencies

Exploitation probability EPSS · FIRST

EPSS probability (%)Percentile among all CVEs

Exploitation signals 4 / 5

KEV catalog (CISA)22 Jan 2026
Exploited in EUVD (ENISA)22 Jan 2026
Used by ransomwareno
EPSS above 10 %48.9%
No account, over the networkyes

What to do

Fix

Apply the vendor’s fix as soon as it is available.

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

Meanwhile

Take the service off the internet or restrict access to it, watch the logs and look for signs of compromise.

Manufacturers (CRA)

Exploited vulnerability in your product: early warning to ENISA within 24 h, then notification within 72 h (Article 14 of the Cyber Resilience Act). The CRA explained

Description ENISA EUVD

A Local File Inclusion (LFI) vulnerability exists in the Webmail Classic UI of Zimbra Collaboration (ZCS) 10.0 and 10.1 because of improper handling of user-supplied request parameters in the RestFilter servlet. An unauthenticated remote attacker can craft requests to the /h/rest endpoint to influence internal request dispatching, allowing inclusion of arbitrary files from the WebRoot directory.

Affected products

Zimbra Collaboration Suite (ZCS)

Weaknesses (CWE)

CWE-98

Open source packages OSV

Affected libraries according to OSV, with fixed versions.

Timeline

22 Dec 2025
Published
22 Jan 2026
Exploitation reported (ENISA)
22 Jan 2026
Added to the KEV catalog
12 Feb 2026
CISA remediation due date
25 Sept 2026
EPSS peak: 48.9%

References

Other exploited vulnerabilities from the same vendor

CVE-2026-73570Zimbra Collaboration Suite (ZCS) OS Command Injection Vulnerability
8.1 · Actively exploited
CVE-2025-48700Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability
4.3 · Background exploitation
CVE-2025-66376Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability
5.9 · Background exploitation
CVE-2020-7796Synacor Zimbra Collaboration Suite (ZCS) Server-Side Request Forgery Vulnerability
9.1 · Background exploitation
CVE-2025-27915Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability
3.5 · Background exploitation
CVE-2019-9621Synacor Zimbra Collaboration Suite (ZCS) Server-Side Request Forgery (SSRF) Vulnerability
7.8 · Background exploitation