CVE-2018-21250
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 Mattermost Server before 5.2.2, 5.1.2, and 4.10.4. It allows remote attackers to cause a denial of service (memory consumption) via crafted image dimensions.
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 confidenceMattermost Server before versions 5.2.2, 5.1.2, and 4.10.4 contains a denial of service vulnerability where remote attackers can cause memory exhaustion by uploading images with crafted (likely excessively large) dimensions. The server appears to allocate memory based on image dimensions without adequate validation, leading to memory consumption that can crash or disable the service.
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< 4.10.4>= 5.1.0, < 5.1.2>= 5.2.0, < 5.2.2CVSS 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
- Required
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/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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Determine Mattermost Server versionLog into the Mattermost System Console and navigate to 'About' > 'Mattermost' to view the version number. Alternatively, use the Mattermost CLI: run `mattermost version` or check the server logs for the version string at startup.Affected if The installed version is lower than 4.10.4, or falls between 5.1.0-5.1.1 or 5.2.0-5.2.1.
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Confirm image upload capability is enabledIn the Mattermost System Console, go to 'Posts' > 'Images' and verify that 'Enable Image Previews' or 'Allow users to upload images' is turned on. This feature is enabled by default in standard installations.Affected if Image uploads are enabled, as the vulnerability is triggered when a user (or attacker) uploads a crafted image file.
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Check for image dimension configurationIn the System Console, review 'Posts' > 'Images' settings for any configured 'Maximum image dimensions' or 'Image preview dimension limits'. Check the config.json file for 'ImageSettings' > 'MaximumImageWidth' or 'MaximumImageHeight' settings.Affected if No maximum dimension limits are configured, meaning the server will attempt to process images of any provided dimensions.
You are affected if your Mattermost Server version is below the fixed releases (4.10.4, 5.1.2, or 5.2.2) AND image uploads are enabled, allowing attackers to trigger memory exhaustion via specially crafted image dimensions.
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 data4.10.45.1.25.2.2
Upgrade Mattermost Server to version 5.2.2, 5.1.2, 4.10.4 or later to patch the vulnerability. Consider implementing image dimension limits or sandboxing image processing as an additional defense-in-depth measure.
- Consultation2.0 h
- Implementation2.0 h
- Testing3.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2018-21250 — 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-2018-21250 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
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