CVE-2026-27740

CVE-2026-27740 is a medium-severity vulnerability in Discourse with a CVSS 3.x base score of 6.1. 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-79.

Key facts

Description

Discourse is an open-source discussion platform. Versions prior to 2026.3.0-latest.1, 2026.2.1, and 2026.1.2 have a cross-site scripting vulnerability that arises because the system trusts the raw output from an AI Large Language Model (LLM) and renders it using htmlSafe in the Review Queue interface without adequate sanitization. A malicious attacker can use valid Prompt Injection techniques to force the AI to return a malicious payload (e.g., tags). When a Staff member (Admin/Moderator) views the flagged post in the Review Queue, the payload executes. Versions 2026.3.0-latest.1, 2026.2.1, and 2026.1.2 contain a patch. As a workaround, temporarily disable AI triage automation scripts.

Frequently asked questions

What is CVE-2026-27740?
Discourse is an open-source discussion platform. Versions prior to 2026.3.0-latest.1, 2026.2.1, and 2026.1.2 have a cross-site scripting vulnerability that arises because the system trusts the raw output from an AI Large Language Model (LLM) and renders it using htmlSafe in the Review Queue interface without adequate sanitization. A malicious attacker can use valid Prompt Injection techniques to force the AI to return a malicious payload (e.g., tags). When a Staff member (Admin/Moderator) views the flagged post in the Review Queue, the payload executes. Versions 2026.3.0-latest.1, 2026.2.1, and 2026.1.2 contain a patch. As a workaround, temporarily disable AI triage automation scripts.
How severe is CVE-2026-27740?
CVE-2026-27740 has a CVSS 3.x base score of 6.1, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2026-27740 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (24th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-27740?
CVE-2026-27740 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-2026-27740?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-27740 have an EU (EUVD) identifier?
Yes. CVE-2026-27740 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-13194.
When was CVE-2026-27740 published?
CVE-2026-27740 was published on 2026-03-19 and last updated on 2026-06-17.

References

Affected products (2)

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