CVE-2021-27646
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 · uneditedUse After Free vulnerability in iscsi_snapshot_comm_core in Synology DiskStation Manager (DSM) before 6.2.3-25426-3 allows remote attackers to execute arbitrary code via crafted web requests.
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 confidenceA Use After Free vulnerability exists in the iscsi_snapshot_comm_core component of Synology DiskStation Manager (DSM). This memory corruption flaw allows remote attackers to execute arbitrary code by sending specially crafted web requests to the affected system, achieving code execution without authentication.
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< 6.2.3-25426-3CVSS 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:3.1/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 checksWork through these to decide whether this CVE applies to you.
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Check DSM versionLog into DSM web interface and go to Control Panel > System > Update & Restore, or run 'cat /etc/VERSION' via SSH to see the installed DSM version number.Affected if The installed version is lower than 6.2.3-25426-3
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Confirm iSCSI service is enabledIn DSM, go to Storage Manager > iSCSI > iSCSI LUN or iSCSI Target to see if any iSCSI targets or LUNs are configured and online. Alternatively, run 'synoiscsi-util status' via SSH to check if the iSCSI service is running.Affected if iSCSI service is actively running with targets or LUNs configured
You are affected if your DSM version is below 6.2.3-25426-3 AND the iSCSI service is enabled with targets or LUNs present.
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.
dbcve · scoped6.2.3-25426-3
Upgrade Synology DSM to version 6.2.3-25426-3 or later to patch the vulnerability. If immediate patching is not possible, restrict network access to the management interface and disable iSCSI services if not required.
DSM 6.2.3-25426-3 or later
- 1. Back up all critical data on the Synology NAS before performing any update
- 2. Log in to Synology DiskStation Manager (DSM) as an administrator
- 3. Navigate to Control Panel > System > Update & Restore (or System > Update & Restore depending on DSM version)
- 4. Click on 'Check for Updates' or manually download DSM version 6.2.3-25426-3 or later from the Synology download center
- 5. Select the downloaded update file and initiate the installation
- 6. Wait for the update to complete and verify the system reboots successfully
- 7. Confirm the DSM version is now 6.2.3-25426-3 or later by checking Control Panel > System > System Information
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation4.0 h
- Implementation4.0 h
- Testing4.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-27646 — 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-2021-27646 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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