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Carddav ServerApplication · Synology

CVE-2017-15887

CRITICAL · 9.8 CVSS v3.0 Published 2017-11-07
Fix available
A fix is available. Upgrade to 6.0.7-0085 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

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 · unedited
An improper restriction of excessive authentication attempts vulnerability in /principals in Synology CardDAV Server before 6.0.7-0085 allows remote attackers to obtain user credentials via a brute-force attack.

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 confidence

Synology CardDAV Server versions prior to 6.0.7-0085 fail to implement proper rate limiting or account lockout mechanisms on the /principals authentication endpoint, allowing remote attackers to perform unlimited credential brute-force attempts until valid user credentials are obtained.

MitigationUpgrade Synology CardDAV Server to version 6.0.7-0085 or later to receive the vendor fix. As interim measures, consider network-level rate limiting, Web Application Firewall rules, or restricting external access to the CardDAV server.

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
Carddav ServerApplication
Affected:< 6.0.7-0085

CVSS 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
High
Integrity
High
Availability
High

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/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 checks

Work through these to decide whether this CVE applies to you.

  1. Identify if Synology CardDAV Server is installed
    Log into Synology DiskStation Manager (DSM) and navigate to Package Center to check if the CardDAV Server package is installed. Alternatively, check for running processes or services related to CardDAV on the system.
    Affected if CardDAV Server package is not installed on the Synology NAS - the system is not affected.
  2. Check the installed CardDAV Server version
    In DSM Package Center, click on CardDAV Server and view the version information. Alternatively, use the command line to query the package version if available (e.g., via synopkg or similar package management tools on Synology).
    Affected if The installed version is prior to 6.0.7-0085 - the vulnerability is present.
  3. Verify if the /principals endpoint is accessible
    From an external or internal client, attempt to access the CardDAV Server /principals endpoint (typically at a URL path like /principals/ or /carddav/principals/) using a web browser or curl command. Check if the endpoint responds to unauthenticated or authenticated requests.
    Affected if The /principals endpoint is reachable from a network where attackers could attempt brute-force attacks - exposure risk exists.
  4. Confirm lack of rate limiting or account lockout
    Test the authentication mechanism by making multiple failed login attempts to the CardDAV Server. Observe whether any rate limiting (delays, CAPTCHAs) or account lockout (account disabled after N failed attempts) occurs. Document the behavior.
    Affected if Multiple failed authentication attempts proceed without any enforced delays, CAPTCHA challenges, or account lockout - the vulnerability is exploitable.

A Synology NAS with CardDAV Server installed at a version prior to 6.0.7-0085 and with the /principals endpoint exposed to untrusted networks is affected by this lack of rate limiting, allowing credential brute-force attacks.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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.

dbcve · scoped
Upgrade available Upgrade to 6.0.7-0085 or later
Fixed in 6.0.7-0085
Interim mitigation

Upgrade Synology CardDAV Server to version 6.0.7-0085 or later to receive the vendor fix. As interim measures, consider network-level rate limiting, Web Application Firewall rules, or restricting external access to the CardDAV server.

Recommended fix High confidence

CardDAV Server 6.0.7-0085 or later

  1. Access Synology DiskStation Manager (DSM) as administrator
  2. Open Package Center and locate CardDAV Server
  3. Check current installed version of CardDAV Server (should be below 6.0.7-0085)
  4. In Package Center, click Update to install the latest available version of CardDAV Server
  5. Alternatively, manually download the update from Synology's download center and install via Manual Install in Package Center
  6. Verify the updated version is 6.0.7-0085 or later
  7. Confirm the /principals endpoint now enforces proper rate limiting on authentication attempts

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Carddav Server Scoped from the published advisory
  • Consultation3.0 h
  • Implementation2.0 h
  • Testing3.0 h
  • Review / QA2.0 h
10.0 hours of engineering $1,770
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2017-15887 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • 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
  • No spam, self-promotion, credentials, or personal data