CVE-2019-9670
CVE-2019-9670 is a security flaw in Synacor Zimbra Collaboration Suite (ZCS), email and calendar software companies run on their own servers. Attackers can read files on Synacor Zimbra Collaboration Suite (ZCS) that should be out of reach. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 10 Jan 2022.[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 an improper restriction of XML external entity reference in Synacor Zimbra Collaboration Suite (ZCS). In its words: “Synacor Zimbra Collaboration Suite (ZCS) contains an improper restriction of XML external entity (XXE) vulnerability in the mailboxd component.”[1]
The CVE record adds: “mailboxd component in Synacor Zimbra Collaboration Suite 8.7.x before 8.7.11p10 has an XML External Entity injection (XXE) vulnerability, as demonstrated by Autodiscover/Autodiscover.xml.”[2]
The underlying weakness is XML external entity (CWE-611), in MITRE’s list of common software weaknesses.
It scores 9.8 out of 10 on the Common Vulnerability Scoring System, which rates it critical, 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 10 Jan 2022, 957 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 10 Jul 2022 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 over 99%. 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 updates per vendor instructions.”[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 10 Jul 2022 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 9.8.[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 over 99%.[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-2019-9621: server-side request forgery (SSRF) ·
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 XML external entity flaws
- CVE-2025-58360, OSGeo GeoServer: improper restriction of XML external entity reference ·
- CVE-2025-2776, SysAid On-Prem: on-prem improper restriction of XML external entity reference ·
- CVE-2025-2775, SysAid On-Prem: on-prem improper restriction of XML external entity reference ·
- CVE-2023-45727, North Grid Proself: improper restriction of XML external entity (XXE) reference ·
- CVE-2024-34102, Adobe Commerce and Magento Open Source: improper restriction of XML external entity reference (XXE) ·
Added the same day
- CVE-2021-36260, Hikvision Security cameras web server: improper input validation ·
- CVE-2021-27860, FatPipe WARP, IPVPN, and MPVPN software: WARP, IPVPN, and MPVPN configuration upload exploit ·
- CVE-2021-22017, VMware vCenter Server: improper access control ·
- CVE-2020-6572, Google Chrome Media: use-after-free ·
- CVE-2019-7609, Elastic Kibana: arbitrary code execution ·
Every Synacor flaw on CISA’s list · Everything added in January 2022
References
- ^ Cybersecurity and Infrastructure Security Agency. “Synacor Zimbra Collaboration Suite (ZCS) Improper Restriction of XML External Entity Reference”. Known Exploited Vulnerabilities Catalog, added 10 Jan 2022.
- ^ National Institute of Standards and Technology. “CVE-2019-9670 Detail”. National Vulnerability Database, published 29 May 2019.
- ^ Synacor. Advisories and fixes: wiki.zimbra.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 1.000, percentile 100.0, 31 Oct 2026.
- CVE Program. “CVE-2019-9670”. 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.