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CVE Record

CVE-2021-37865: Server-side Denial of Service while processing a specifically crafted GIF file

Mattermost 6.2 and earlier fails to sufficiently process a specifically crafted GIF file when it is uploaded while drafting a post, which allows authenticated users to cause resource exhaustion while processing the file, resulting in server-side Denial of Service.

MediumCVSS 4.3Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

An authenticated Mattermost user could upload a specially crafted GIF while drafting a post and make the server consume excessive resources. The known impact is availability degradation or denial of service, not data theft or data modification.

Executive priority

Treat this as a moderate availability risk. It is not described as a data breach issue, but a compromised or malicious user could disrupt collaboration services if affected Mattermost versions remain exposed.

Technical view

CVE-2021-37865 is a CWE-400 resource-exhaustion flaw in Mattermost 6.2 and earlier. The CVSS 3.1 vector is AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L, reflecting network reachability, low attack complexity, required authentication, and limited availability impact.

Likely exposure

Exposure is most relevant to Mattermost deployments at 6.2 or earlier, especially where many users can authenticate and upload files. The bundle lists affected Mattermost versions including 6.1.1, 6.0.4, 5.39.3, and 5.37.6.

Exploitation context

The source bundle does not show CISA KEV listing or evidence of active exploitation. Abuse requires an authenticated Mattermost user and a crafted GIF upload during post drafting, so insider, compromised-account, or broadly provisioned workspace scenarios matter most.

Researcher notes

Evidence supports authenticated server-side denial of service through crafted GIF processing during draft upload. The provided bundle does not include exploit details, confirmed exploitation, or specific fixed-version text, so validation should stay focused on version exposure and vendor advisories.

Mitigation direction

  • Check Mattermost security updates for the vendor-designated fixed release.
  • Upgrade affected Mattermost deployments according to vendor guidance.
  • Prioritize instances running Mattermost 6.2 or earlier.
  • Review authenticated user access and remove unnecessary accounts.
  • Monitor server resource usage around file uploads and post drafting.

Validation and detection

  • Inventory Mattermost server versions across production and staging.
  • Compare deployed versions with the affected versions in the CVE record.
  • Review authentication scope and who can upload files.
  • Check logs and monitoring for upload-related resource spikes.
  • Confirm remediation against Mattermost security guidance.
Prepared
Confidence
high
Sources
4

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-400: Exact CWE lookup

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cve · low confidence lookup

CVE-2021-37865 mapping review

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
4.3 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
0Timeline events
0ADP providers
3Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
4.3CVSS 3.1MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L2.81.4Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

4.3Medium
CVSS 3.1 vector shape for CVE-2021-37865Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
MattermostMattermostunspecified, 6.1.1, 6.0.4, 5.39.3, 5.37.6Listed
Weakness

CWE details

CWE-400

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.