CVE-2020-8633
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 · uneditedAn issue was discovered in Zimbra Collaboration Suite (ZCS) before 8.8.15 Patch 7. When grantors revoked a shared calendar in Outlook, the calendar stayed mounted and accessible.
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 · moderate confidenceIn ZCS before 8.8.15 Patch 7, a calendar sharing revocation logic flaw existed where server-side permissions were not properly updated when users revoked shared calendar access from Outlook. The calendar remained mounted and accessible to the grantee despite the revocation action, representing an access control bypass.
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= 8.8.15CVSS 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
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- Low
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
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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Check Zimbra Collaboration Suite versionRun 'zmcontrol -v' or 'zmlocalconfig -s zimbra_version' from the ZCS server command line, or inspect the installed package version via the package managerAffected if The installed version is 8.8.15 or any version lower than 8.8.15 (versions < 8.8.15)
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Verify calendar sharing is enabledCheck the ZCS configuration via 'zmprov getServer <server_id> zimbraFeatureCalendarSharingEnabled' or inspect the admin console under Server Settings > FeaturesAffected if Calendar sharing feature is enabled (value returns TRUE)
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Identify active calendar sharesUse 'zmprov --markdown getCalendarFreeBusy' or the admin console to list all shared calendars in the environment, noting which users have granted access to their calendarsAffected if Any calendar shares exist in the system
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Inspect for stale shares from pre-patch revocationsCross-reference calendar share records with user accounts that previously revoked access from Outlook clients; query shares via 'zmprov gr' commands or review audit logs for revocation actions that may not have propagated correctlyAffected if Calendar shares exist for users who attempted to revoke Outlook calendar sharing but the shares remain active in the system
You are affected if your ZCS version is 8.8.15 or earlier AND calendar sharing was used with revocation actions attempted from Outlook, as stale shares may still grant access despite revocation.
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
Upgrade ZCS to version 8.8.15 Patch 7 or later. Additionally, review existing calendar sharing permissions to identify and manually revoke any stale shares that may have persisted from before the patch.
- Consultation3.0 h
- Implementation6.0 h
- Testing4.0 h
- Review / QA2.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2020-8633 — 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-2020-8633 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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