How severe is CVE-2026-27166?

CVE-2026-27166 has a CVSS 3.x base score of 4.1, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is none, integrity low, and availability none.

Is CVE-2026-27166 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (8th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-27166?

CVE-2026-27166 primarily affects Discourse. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-27166?

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

Does CVE-2026-27166 have an EU (EUVD) identifier?

Yes. CVE-2026-27166 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-13187.

When was CVE-2026-27166 published?

CVE-2026-27166 was published on 2026-03-19 and last updated on 2026-06-17.

CVE-2026-27166

CVE-2026-27166 is a medium-severity vulnerability in Discourse with a CVSS 3.x base score of 4.1. 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-80.

Key facts

Severity: Medium (CVSS 3.x base score 4.1)
EPSS exploit prediction: 0% (8th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-13187
Weakness: CWE-80
Affected product: Discourse
Published: 2026-03-19
Last modified: 2026-06-17

Description

Discourse is an open source discussion platform. Prior to versions 2026.3.0-latest.1, 2026.2.1 and 2026.1.2, insufficient cleanup in the default Codepen allowed iframes value allows an attacker to trick a user into changing the URL of the main page. This issue has been fixed in versions 2026.3.0-latest.1, 2026.2.1 and 2026.1.2. To workaround this issue, remove Codepen from the list of allowed iframes.

Frequently asked questions

What is CVE-2026-27166?: Discourse is an open source discussion platform. Prior to versions 2026.3.0-latest.1, 2026.2.1 and 2026.1.2, insufficient cleanup in the default Codepen allowed iframes value allows an attacker to trick a user into changing the URL of the main page. This issue has been fixed in versions 2026.3.0-latest.1, 2026.2.1 and 2026.1.2. To workaround this issue, remove Codepen from the list of allowed iframes.
How severe is CVE-2026-27166?: CVE-2026-27166 has a CVSS 3.x base score of 4.1, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is none, integrity low, and availability none.
Is CVE-2026-27166 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (8th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-27166?: CVE-2026-27166 primarily affects Discourse. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-27166?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-27166 have an EU (EUVD) identifier?: Yes. CVE-2026-27166 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-13187.
When was CVE-2026-27166 published?: CVE-2026-27166 was published on 2026-03-19 and last updated on 2026-06-17.

References

Affected products (2)

cpe:2.3:a:discourse:discourse:*:*:*:*:*:*:*:*
cpe:2.3:a:discourse:discourse:2026.3.0:*:*:*:latest:*:*:*

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