CVE-2019-9621
CVE-2019-9621 is a security flaw in Synacor Zimbra Collaboration Suite (ZCS), email and calendar software companies run on their own servers. Attackers can make Synacor Zimbra Collaboration Suite (ZCS) send requests into the network behind it. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 7 Jul 2025.[1]
Synacor Zimbra Collaboration Suite (ZCS) is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. Synacor has published a fix or advice.
Description
CISA calls it a server-side request forgery (SSRF) in Synacor Zimbra Collaboration Suite (ZCS). In its words: “Synacor Zimbra Collaboration Suite (ZCS) contains a server-side request forgery (SSRF) vulnerability via the ProxyServlet component.”[1]
The CVE record adds: “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.”[2]
The underlying weakness is server-side request forgery (CWE-918), CWE-807, in MITRE’s list of common software weaknesses.
It scores 7.5 out of 10 on the Common Vulnerability Scoring System, which rates it high, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record doesn’t list version ranges for it; Synacor’s advisory has them[3]. CISA names the product as Synacor Zimbra Collaboration Suite (ZCS).
Most families won’t have Synacor Zimbra Collaboration Suite (ZCS); it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 7 Jul 2025, 2,260 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 28 Jul 2025 to fix it.[1]
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 81%. That’s in the top 1% of the flaws it scores.[4]
CISA assesses it as automatable: attackers can run it against many targets at once.
CISA doesn’t say who was attacked, or how.
Fix
Synacor has published a fix or advice.[3] 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.”[1]
- Check whether you use it.Synacor Zimbra Collaboration Suite (ZCS) is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
- Send this page to your IT person.Ask them to confirm it’s fixed, or not in use. CISA gave US government agencies until 28 Jul 2025 to fix it.
- If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.
You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 7.5.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at 81%.[4] |
See also
Other Synacor Zimbra Collaboration Suite (ZCS) flaws
- CVE-2026-73570: OS command injection ·
- CVE-2025-48700: cross-site scripting ·
- CVE-2025-66376: cross-site scripting ·
- CVE-2025-68645: PHP remote file inclusion ·
- CVE-2025-27915: cross-site scripting ·
- CVE-2024-27443: cross-site scripting (XSS) ·
Other Synacor flaws
- CVE-2020-7796, Synacor Zimbra Collaboration Suite: (ZCS) server-side request forgery ·
- CVE-2022-24682, Synacor Zimbra Collaborate Suite (ZCS): cross-site scripting ·
Other server-side request forgery flaws
- CVE-2026-96655, Plex Media Server: server-side request forgery (SSRF) ·
- CVE-2026-96652, Plex Media Server: server-side request forgery (SSRF) ·
- CVE-2026-83548, SonicWall SMA1000 Appliances: server-side request forgery ·
- CVE-2026-64849, MLflow: server-side request forgery ·
- CVE-2026-15409, SonicWall SMA1000 Appliances: server-side request forgery ·
Added the same day
- CVE-2019-5418, Rails Ruby on Rails: path traversal ·
- CVE-2016-10033, PHPMailer: command injection ·
- CVE-2014-3931, Looking Glass Multi-Router Looking Glass (MRLG): buffer overflow ·
Every Synacor flaw on CISA’s list · Everything added in July 2025
References
- ^ Cybersecurity and Infrastructure Security Agency. “Synacor Zimbra Collaboration Suite (ZCS) Server-Side Request Forgery (SSRF) Vulnerability”. Known Exploited Vulnerabilities Catalog, added 7 Jul 2025.
- ^ National Institute of Standards and Technology. “CVE-2019-9621 Detail”. National Vulnerability Database, published 30 Apr 2019.
- ^ Synacor. Advisories and fixes: wiki.zimbra.com, wiki.zimbra.com, blog.zimbra.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.810, percentile 99.6, 31 Oct 2026.
- CVE Program. “CVE-2019-9621”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.