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CVE Record

CVE-2021-43850: Denial of Service in discourse

Discourse is an open source platform for community discussion. In affected versions admins users can trigger a Denial of Service attack via the `/message-bus/_diagnostics` path. The impact of this vulnerability is greater on multisite Discourse instances (where multiple forums are served from a single application server) where any admin user on any of the forums are able to visit the `/message-bus/_diagnostics` path. The problem has been patched. Please upgrade to 2.8.0.beta10 or 2.7.12. No workarounds for this issue exist.

MediumCVSS 6.8Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2021-43850 is a denial-of-service flaw in Discourse. An authenticated admin can trigger service disruption through the diagnostics endpoint. The business risk is availability loss, especially for multisite deployments where one forum admin can affect multiple forums served by the same application server.

Executive priority

Prioritize remediation for internet-facing or multisite Discourse platforms, especially where community uptime is business-critical. This is not a data theft issue based on available sources, but it can disrupt availability.

Technical view

Affected Discourse versions before 2.7.12 and 2.8.0 beta versions before 2.8.0.beta10 allow admin users to trigger a denial of service via /message-bus/_diagnostics. The CVSS 3.1 score is 6.8 with high availability impact and no confidentiality or integrity impact identified.

Likely exposure

Exposure is limited to Discourse deployments running affected versions. Multisite Discourse instances have higher blast radius because an admin on any hosted forum may impact the shared application server.

Exploitation context

The source bundle does not show active exploitation, and CISA KEV is false. Exploitation requires low privileges, specifically admin-level access in Discourse, and user interaction is reflected in the CVSS vector.

Researcher notes

The public advisory identifies CWE-20 and a patch commit, but the provided bundle does not include detailed root-cause analysis beyond the diagnostics path behavior. Avoid assuming broader products, privilege levels, or exploitation beyond the cited Discourse advisory.

Mitigation direction

  • Upgrade stable deployments to Discourse 2.7.12 or later.
  • Upgrade beta deployments to 2.8.0.beta10 or later.
  • Do not treat compensating controls as a complete fix; sources state no workaround exists.
  • If unable to upgrade, check current Discourse vendor guidance.

Validation and detection

  • Inventory all Discourse instances and record exact running versions.
  • Identify whether any instance uses multisite hosting.
  • Review admin account scope across affected forums.
  • Confirm upgraded instances are at or above the fixed versions.
  • Review logs for access to the diagnostics path during the exposure window.
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-20: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2021-43850 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
Medium
CVSS
6.8 (3.1)
Known Exploited
No
Published

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

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
6.8CVSS 3.1MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:N/I:N/A:H2.34Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

6.8Medium
CVSS 3.1 vector shape for CVE-2021-43850Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

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
discoursediscourse< 2.7.12, >= 2.8.0.beta, < 2.8.0.beta10Listed
Weakness

CWE details

CWE-20

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