Synacor Zimbra Collaboration Suite (ZCS) Server-Side Request Forgery (SSRF)
CVE-2019-9621 is a high-severity server-side request forgery vulnerability in Zimbra Collaboration Suite from Synacor, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 8.6.0, 8.7.11, 8.8.9 as the first without the flaw, so updating Zimbra Collaboration Suite to one of those releases or later removes the exposure. CISA added it to the Known Exploited Vulnerabilities catalogue on July 7, 2025, which means attacks have been observed in the wild.
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Update Zimbra Collaboration Suite to 8.6.0 or 8.7.11 or 8.8.9, whichever matches your release line, or a later version.
- CISA's 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.
- Read the advisory on blog.zimbra.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Synacor | Zimbra Collaboration Suite | before 8.6.0; 8.7.0 up to, but not including, 8.7.11; 8.8.0 up to, but not including, 8.8.9; 8.6.0; 8.7.11; 8.8.9; 8.8.10; 8.8.11 | 8.6.0, 8.7.11, 8.8.9 |
Version data comes from NVD's product matching. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- NoneNothing can be modified.
- Availability
- NoneAvailability is not affected.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.5 | High | NVD |
| CVSS 3.1 | 7.5 | High | CISA (ADP) |
| CVSS 2.0 | 5.0 | Medium | NVD |
Official description
Zimbra Collaboration Suite before 8.6 patch 13, 8.7.x before 8.7.11 patch 10, and 8.8.x before 8.8.10 patch 7 or 8.8.x before 8.8.11 patch 3 allows SSRF via the ProxyServlet component.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Server-Side Request Forgery
The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.
How developers prevent this class of flaw
- If there is a known list of applications, IP, hostname, and/or domains to which the product is allowed to communicate, then use allowlists to ensure that outgoing requests are restricted to these known entities. The allowlists could be in the application code or possibly enforced by firewalls or network segmentation.
- If the product is expected to be able to connect to arbitrary IP addresses or domains, consider using a denylist that includes private network addresses, internal domain names, etc. The denylist could be in the application code or possibly enforced by firewalls or network segmentation.
Timeline
- CVE record published.
- Added to CISA's Known Exploited Vulnerabilities catalogue.
- CISA published its SSVC assessment (exploitation: active, automatable: yes, technical impact: partial).
- Deadline for US federal agencies to remediate, set by CISA.
- Record last changed materially (score, affected products, status or references).
References
Advisories
Third-party and government advisories
- blog.tint0.com/2019/03/a-saga-of-code-executions-on-zimbra.htmlThird Party Advisory
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2019-9621US Government Resource
Technical write-ups (may include proof of concept)
- packetstormsecurity.com/files/152487/Zimbra-Collaboration-Autodiscover-Servlet-XXE-ProxyServlet-SSRF.htmlExploit, Third Party Advisory, VDB Entry
- packetstormsecurity.com/files/153190/Zimbra-XML-Injection-Server-Side-Request-Forgery.htmlExploit, Third Party Advisory, VDB Entry
- rapid7.com/db/modules/exploit/linux/http/zimbra_xxe_rceExploit, Third Party Advisory
- exploit-db.com/exploits/46693/Exploit, Third Party Advisory, VDB Entry
Other references
- bugzilla.zimbra.com/show_bug.cgi?id=109127Issue Tracking
Other vulnerabilities in Zimbra Collaboration Suite
- 8.9 High severity
- 8.8 High severity
- 6.1 Medium severity
- 8.8 High severity
- 6.1 Medium severity
- 8.8 High severity
Recent Server-Side Request Forgery vulnerabilities
- 5.5 Medium severity
Spotted an error? Tell us.