Synacor flaws being used in attacks

CISA lists 19 flaws in Synacor products as being used in attacks, most recently on 21 Aug 2026. 6 have been used in ransomware.

What to do

1. Update every Synacor product you use.Install the updates Synacor offers, on every device, and restart when asked. Each flaw below has a fix or clear advice; that’s one of CISA’s conditions for listing it.
2. If someone looks after IT for you, send them this page.Many of these are in equipment you don’t see: routers, firewalls, servers, the office network. Ask them to confirm each one is fixed, or that you don’t use the product.
3. Check anything else in the lookup.Search any app, company or CVE. Not being on CISA’s list doesn’t mean safe: keep updating either way.

Every flaw, newest first

1. Being used in attacksAdded by CISA on 21 Aug 2026
   Synacor Zimbra Collaboration Suite (ZCS)
   CVE-2026-73570Zimbra Collaboration Suite (ZCS) OS Command Injection Vulnerability
   Zimbra Collaboration Suite (ZCS) contains an OS command injection vulnerability which could allow an unauthenticated attacker to send specially crafted SMTP requests that may result in execution of arbitrary operating system commands as the Zimbra user.
   CISA’s required actionApply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Read all

   Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
   CVE recordNVD
2. Being used in attacksAdded by CISA on 20 Apr 2026
   Synacor Zimbra Collaboration Suite (ZCS)
   CVE-2025-48700Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability
   Synacor Zimbra Collaboration Suite (ZCS) contains a cross-site scripting vulnerability that could allow attackers to execute arbitrary JavaScript within the user's session, potentially leading to unauthorized access to sensitive information.
   CISA’s required actionApply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
   CVE recordNVD
3. Being used in attacksAdded by CISA on 18 Mar 2026
   Synacor Zimbra Collaboration Suite (ZCS)
   CVE-2025-66376Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability
   Synacor Zimbra Collaboration Suite (ZCS) contains a cross-site scripting vulnerability in the Classic UI where attackers could abuse Cascading Style Sheets (CSS) @import directives in email HTML.
   CISA’s required actionApply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
   CVE recordNVD
4. Being used in attacksAdded by CISA on 17 Feb 2026
   Synacor Zimbra Collaboration Suite
   CVE-2020-7796Synacor Zimbra Collaboration Suite (ZCS) Server-Side Request Forgery Vulnerability
   Synacor Zimbra Collaboration Suite (ZCS) contains a server-side request forgery vulnerability if WebEx zimlet installed and zimlet JSP is enabled.
   CISA’s required actionApply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
   CVE recordNVD
5. Being used in attacksAdded by CISA on 22 Jan 2026
   Synacor Zimbra Collaboration Suite (ZCS)
   CVE-2025-68645Synacor Zimbra Collaboration Suite (ZCS) PHP Remote File Inclusion Vulnerability
   Synacor Zimbra Collaboration Suite (ZCS) contains a PHP remote file inclusion vulnerability that could allow for remote attackers to craft requests to the /h/rest endpoint to influence internal request dispatching, allowing inclusion of arbitrary files from the WebRoot directory.
   CISA’s required actionApply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
   CVE recordNVD
6. Being used in attacksAdded by CISA on 7 Oct 2025
   Synacor Zimbra Collaboration Suite (ZCS)
   CVE-2025-27915Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability
   Synacor Zimbra Collaboration Suite (ZCS) contains a cross-site scripting vulnerability that 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 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.
   CISA’s required actionApply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
   CVE recordNVD
7. Being used in attacksAdded by CISA on 7 Jul 2025
   Synacor Zimbra Collaboration Suite (ZCS)
   CVE-2019-9621Synacor Zimbra Collaboration Suite (ZCS) Server-Side Request Forgery (SSRF) Vulnerability
   Synacor Zimbra Collaboration Suite (ZCS) contains a server-side request forgery (SSRF) vulnerability via the ProxyServlet component.
   CISA’s required actionApply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
   CVE recordNVD
8. Being used in attacksAdded by CISA on 19 May 2025
   Synacor Zimbra Collaboration Suite (ZCS)
   CVE-2024-27443Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting (XSS) Vulnerability
   Zimbra Collaboration contains a cross-site scripting (XSS) vulnerability in the CalendarInvite feature of the Zimbra webmail classic user interface. An attacker can exploit this vulnerability via an email message containing a crafted calendar header, leading to the execution of arbitrary JavaScript code.
   CISA’s required actionApply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
   CVE recordNVD
9. Being used in attacksAdded by CISA on 25 Feb 2025
   Synacor Zimbra Collaboration Suite (ZCS)
   CVE-2023-34192Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting (XSS) Vulnerability
   Synacor Zimbra Collaboration Suite (ZCS) contains a cross-site scripting (XSS) vulnerability that allows a remote authenticated attacker to execute arbitrary code via a crafted script to the /h/autoSaveDraft function.
   CISA’s required actionApply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
   CVE recordNVD
10. Being used in attacksAdded by CISA on 3 Oct 2024
    Synacor Zimbra Collaboration Suite (ZCS)
    CVE-2024-45519Synacor Zimbra Collaboration Suite (ZCS) Command Execution Vulnerability
    Synacor Zimbra Collaboration Suite (ZCS) contains an unspecified vulnerability in the postjournal service that may allow an unauthenticated user to execute commands.
    CISA’s required actionApply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.
    CVE recordNVD
11. Being used in attacksAdded by CISA on 27 Jul 2023
    Synacor Zimbra Collaboration Suite (ZCS)
    CVE-2023-37580Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting (XSS) Vulnerability
    Synacor Zimbra Collaboration Suite (ZCS) contains a cross-site scripting vulnerability impacting the confidentiality and integrity of data.
    CISA’s required actionApply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.
    CVE recordNVD
12. Being used in attacksAdded by CISA on 3 Apr 2023
    Synacor Zimbra Collaboration Suite (ZCS)
    CVE-2022-27926Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting (XSS) Vulnerability
    Synacor Zimbra Collaboration Suite (ZCS) contains a cross-site scripting vulnerability by allowing an endpoint URL to accept parameters without sanitizing.
    CISA’s required actionApply updates per vendor instructions.
    CVE recordNVD
13. Being used in attacksUsed in ransomwareAdded by CISA on 20 Oct 2022
    Synacor Zimbra Collaboration Suite (ZCS)
    CVE-2022-41352Synacor Zimbra Collaboration Suite (ZCS) Arbitrary File Upload Vulnerability
    Synacor Zimbra Collaboration Suite (ZCS) allows an attacker to upload arbitrary files using cpio package to gain incorrect access to any other user accounts.
    CISA’s required actionApply updates per vendor instructions.
    CVE recordNVD
14. Being used in attacksUsed in ransomwareAdded by CISA on 11 Aug 2022
    Synacor Zimbra Collaboration Suite (ZCS)
    CVE-2022-37042Synacor Zimbra Collaboration Suite (ZCS) Authentication Bypass Vulnerability
    Synacor Zimbra Collaboration Suite (ZCS) contains an authentication bypass vulnerability in MailboxImportServlet. This vulnerability was chained with CVE-2022-27925 which allows for unauthenticated remote code execution.
    CISA’s required actionApply updates per vendor instructions.
    CVE recordNVD
15. Being used in attacksUsed in ransomwareAdded by CISA on 11 Aug 2022
    Synacor Zimbra Collaboration Suite (ZCS)
    CVE-2022-27925Synacor Zimbra Collaboration Suite (ZCS) Arbitrary File Upload Vulnerability
    Synacor Zimbra Collaboration Suite (ZCS) contains flaw in the mboximport functionality, allowing an authenticated attacker to upload arbitrary files to perform remote code execution. This vulnerability was chained with CVE-2022-37042 which allows for unauthenticated remote code execution.
    CISA’s required actionApply updates per vendor instructions.
    CVE recordNVD
16. Being used in attacksUsed in ransomwareAdded by CISA on 4 Aug 2022
    Synacor Zimbra Collaboration Suite (ZCS)
    CVE-2022-27924Synacor Zimbra Collaboration Suite (ZCS) Command Injection Vulnerability
    Synacor Zimbra Collaboration Suite (ZCS) allows an attacker to inject memcache commands into a targeted instance which causes an overwrite of arbitrary cached entries.
    CISA’s required actionApply updates per vendor instructions.
    CVE recordNVD
17. Being used in attacksUsed in ransomwareAdded by CISA on 19 Apr 2022
    Synacor Zimbra Collaboration Suite (ZCS)
    CVE-2018-6882Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting (XSS) Vulnerability
    Synacor Zimbra Collaboration Suite (ZCS) contains a cross-site scripting vulnerability that might allow remote attackers to inject arbitrary web script or HTML.
    CISA’s required actionApply updates per vendor instructions.
    CVE recordNVD
18. Being used in attacksUsed in ransomwareAdded by CISA on 25 Feb 2022
    Synacor Zimbra Collaborate Suite (ZCS)
    CVE-2022-24682Synacor Zimbra Collaborate Suite (ZCS) Cross-Site Scripting Vulnerability
    Synacor Zimbra Collaboration Suite (ZCS) contains a cross-site scripting (XSS) vulnerability in the Calendar feature that allows an attacker to execute arbitrary code.
    CISA’s required actionApply updates per vendor instructions.
    CVE recordNVD
19. Being used in attacksAdded by CISA on 10 Jan 2022
    Synacor Zimbra Collaboration Suite (ZCS)
    CVE-2019-9670Synacor Zimbra Collaboration Suite (ZCS) Improper Restriction of XML External Entity Reference
    Synacor Zimbra Collaboration Suite (ZCS) contains an improper restriction of XML external entity (XXE) vulnerability in the mailboxd component.
    CISA’s required actionApply updates per vendor instructions.
    CVE recordNVD

From CISA’s Known Exploited Vulnerabilities catalog, updated 21 Oct 2026 (version 2026.10.21). CISA’s required actions are written for US government agencies. Synacor on CISA’s site.