CVE-2020-12846
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedZimbra before 8.8.15 Patch 10 and 9.x before 9.0.0 Patch 3 allows remote code execution via an avatar file. There is potential abuse of /service/upload servlet in the webmail subsystem. A user can upload executable files (exe,sh,bat,jar) in the Contact section of the mailbox as an avatar image for a contact. A user will receive a "Corrupt File" error, but the file is still uploaded and stored locally in /opt/zimbra/data/tmp/upload/, leaving it open to possible remote execution.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceZimbra Collaboration Suite versions before 8.8.15 Patch 10 and 9.x before 9.0.0 Patch 3 contain a file upload vulnerability in the /service/upload servlet of the webmail subsystem. The contact avatar upload feature does not properly validate file types, allowing users to upload executable files (exe, sh, bat, jar) disguised as avatar images. Although the UI displays a 'Corrupt File' error, the files are still saved to /opt/zimbra/data/tmp/upload/, creating a path for potential remote code execution.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data< 8.8.15= 8.8.15= 9.0.0CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- Low
- User interaction
- Required
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify installed Zimbra versionRun 'zmcontrol -v' as the zimbra user or check the installed package version using 'rpm -q zimbra-pkg'Affected if Version is 8.8.15 (any patch level below 10), 9.0.0 (any patch level below 3), or any 9.x version below Patch 3
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Verify contact avatar upload feature accessibilityConfirm the /service/upload servlet is reachable by attempting a local HTTP request to 'http://localhost:8080/service/upload' or checking the servlet is not disabled in the Zimbra configurationAffected if The servlet responds and is accessible
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Inspect upload temporary directory for suspicious filesList all files in /opt/zimbra/data/tmp/upload/ using 'ls -la /opt/zimbra/data/tmp/upload/' and check for executable extensionsAffected if Files with extensions .exe, .sh, .bat, or .jar are present in this directory
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Review webmail access logs for upload servlet activityExamine /opt/zimbra/log/nginx.access.log or the mailboxd access logs for POST requests to /service/upload, looking for unusual file types in the request bodyAffected if Logs show uploads of files with executable extensions to the avatar endpoint
A user is affected if their Zimbra installation version falls within the vulnerable range AND the contact avatar upload feature is accessible, with potentially malicious executable files present in the upload directory.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor data8.8.15
Apply Zimbra patch 8.8.15 Patch 10 or 9.0.0 Patch 3 to fix the file type validation in the contact avatar upload functionality, and audit/clean any existing malicious files in /opt/zimbra/data/tmp/upload/.
- Consultation3.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA2.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2020-12846 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2020-12846 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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