How severe is CVE-2026-21865?

CVE-2026-21865 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires high privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.

Is CVE-2026-21865 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (13th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-21865?

CVE-2026-21865 primarily affects Discourse. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-21865?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-21865 have an EU (EUVD) identifier?

Yes. CVE-2026-21865 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-4874.

When was CVE-2026-21865 published?

CVE-2026-21865 was published on 2026-01-28 and last updated on 2026-06-17.

CVE-2026-21865

CVE-2026-21865 is a medium-severity vulnerability in Discourse with a CVSS 3.x base score of 6.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-862.

Key facts

Severity: Medium (CVSS 3.x base score 6.5)
EPSS exploit prediction: 0% (13th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-4874
Weakness: CWE-862
Affected product: Discourse
Published: 2026-01-28
Last modified: 2026-06-17

Description

Discourse is an open source discussion platform. In versions prior to 3.5.4, 2025.11.2, 2025.12.1, and 2026.1.0, moderators can convert some personal messages to public topics when they shouldn't have access. This issue is patched in versions 3.5.4, 2025.11.2, 2025.12.1, and 2026.1.0. As a workaround, site admin can temporarily revoke the moderation role from untrusted moderators or remove the moderator group from the "personal message enabled groups" site setting until the Discourse instance has been upgraded to a version that has been patched.

Frequently asked questions

What is CVE-2026-21865?: Discourse is an open source discussion platform. In versions prior to 3.5.4, 2025.11.2, 2025.12.1, and 2026.1.0, moderators can convert some personal messages to public topics when they shouldn't have access. This issue is patched in versions 3.5.4, 2025.11.2, 2025.12.1, and 2026.1.0. As a workaround, site admin can temporarily revoke the moderation role from untrusted moderators or remove the moderator group from the "personal message enabled groups" site setting until the Discourse instance has been upgraded to a version that has been patched.
How severe is CVE-2026-21865?: CVE-2026-21865 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires high privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.
Is CVE-2026-21865 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (13th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-21865?: CVE-2026-21865 primarily affects Discourse. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-21865?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-21865 have an EU (EUVD) identifier?: Yes. CVE-2026-21865 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-4874.
When was CVE-2026-21865 published?: CVE-2026-21865 was published on 2026-01-28 and last updated on 2026-06-17.

References

https://github.com/discourse/discourse/security/advisories/GHSA-4777-wrv5-3g39

Affected products (3)

cpe:2.3:a:discourse:discourse:*:*:*:*:stable:*:*:*
cpe:2.3:a:discourse:discourse:2025.12.0:*:*:*:stable:*:*:*
cpe:2.3:a:discourse:discourse:2026.1.0:*:*:*:stable:*:*:*

More vulnerabilities in Discourse

CVE-2021-41163 — Critical (CVSS 10.0): Discourse is an open source platform for community discussion. In affected versions maliciously crafted requests could…
CVE-2025-53102 — Critical (CVSS 9.8): Discourse is an open-source community discussion platform. Prior to version 3.4.7 on the `stable` branch and version…
CVE-2025-48877 — Critical (CVSS 9.8): Discourse is an open-source discussion platform. Prior to version 3.4.4 of the `stable` branch, version 3.5.0.beta5 of…
CVE-2022-36066 — Critical (CVSS 9.1): Discourse is an open source discussion platform. In versions prior to 2.8.9 on the `stable` branch and prior to…
CVE-2022-39356 — High (CVSS 8.9): Discourse is a platform for community discussion. Users who receive an invitation link that is not scoped to a single…
CVE-2023-22468 — High (CVSS 8.8): Discourse is an open source platform for community discussion. Versions prior to 2.8.13 (stable), 3.0.0.beta16 (beta)…

All CVEs affecting Discourse →

Other CWE-862 (Missing Authorization) vulnerabilities

CVE-2026-0092 — Critical (CVSS 10.0): In Package Manager, there is a possible device lock controller bypass due to a missing permission check. This could…
CVE-2026-33712 — Critical (CVSS 10.0): Typebot is a chatbot builder tool. In versions 3.15.2 and prior, the preview chat endpoint (POST…
CVE-2026-2031 — Critical (CVSS 10.0): An Improper Access Control vulnerability in several internal API endpoints for Google Cloud Application Integration…
CVE-2026-34976 — Critical (CVSS 10.0): Dgraph is an open source distributed GraphQL database. Prior to 25.3.1, the restoreTenant admin mutation is missing…
CVE-2025-30416 — Critical (CVSS 10.0): Sensitive data disclosure and manipulation due to missing authorization. The following products are affected: Acronis…
CVE-2025-45854 — Critical (CVSS 10.0): /server/executeExec of JEHC-BPM 2.0.1 allows attackers to execute arbitrary code via execParams.

Browse all CWE-862 (Missing Authorization) vulnerabilities →