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CVE-2026-91121

Discourse: Chat upload filenames rendered as raw HTML in excerpts

CVSS 3.1 5.0 MEDIUMCheck source for fixed versionsKEV status unknown

Original advisory

Historical advisory recorded 23 Oct 2026 15:48:27 UTC. Read the latest advisory.

cve-program · CVE-2026-91121

Published

Discourse is an open-source discussion platform. Prior to 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0, attacker-controlled upload filenames used in chat message excerpts were rendered as unescaped HTML. A user able to upload a file and send chat content could place markup in a filename that was then interpreted by chat channel lists, chat summary emails, pinned message bars, reply previews, thread previews, and other excerpt renderers. The issue allowed trusted-HTML injection that altered rendered excerpt content, but JavaScript execution was not demonstrated with default Content Security Policy settings. The advisory states that no confidentiality, integrity, or availability impact was identified, while its structured scoring metadata separately assigns low integrity impact. Sites that disable or relax the default CSP have increased exposure. This issue is fixed in versions 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0.

Read the publisher's advisory

Affected versions, risk and source history

cve-program · CVE-2026-91121

Published

discourse

Vendor product

Publisher's version information

Shown as published. These rules are not interpreted as NuGet package version ranges.

{
                    "vendor": "discourse",
                    "product": "discourse",
                    "versions": [
                        {
                            "version": "< 2026.8.0",
                            "status": "affected"
                        },
                        {
                            "version": ">= 2026.7.0-latest, < 2026.7.2",
                            "status": "affected"
                        },
                        {
                            "version": ">= 2026.6.0-latest, < 2026.6.3",
                            "status": "affected"
                        },
                        {
                            "version": ">= 2026.1.0-latest, < 2026.1.8",
                            "status": "affected"
                        }
                    ]
                }

Original source record · Cite this exact observation · Complete original publisher JSON