CVE-2026-91121

MEDIUMPre-NVD 5.05.0
EchelonGraph scoreLOW confidence

This medium-severity CVE scores 5.0 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit-prediction score not yet available (the EPSS model rescores nightly; freshly-published CVEs typically appear within 48 hours). GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: secondary
5.0EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: —CVSS: 5.0Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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.

CVSS v3
5.0
EG Score
5.0(low)
EG Risk
23(Track)
EG Risk 23/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity50% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
—
EPSS %ILE
—
KEV
Not listed

Published

September 24, 2026

Last Modified

September 24, 2026

Advisory Details (6)

Auto-updated Sep 24, 2026
Patch available. Sources: github, github_pr, github_commit.
github_commit

commit af197941f761 (discourse/discourse)

Fix landed in discourse/discourse commit af197941f761 — awaiting tagged release

https://github.com/discourse/discourse/commit/af197941f7613a3845cba21d217641c77c8ef836
github_commit

commit 9d6f5e64a1cb (discourse/discourse)

Fix landed in discourse/discourse commit 9d6f5e64a1cb — awaiting tagged release

https://github.com/discourse/discourse/commit/9d6f5e64a1cb68e8208520e4209b361e14f7394b
github_commit

commit 6e7a181909c3 (discourse/discourse)

Fix landed in discourse/discourse commit 6e7a181909c3 — awaiting tagged release

https://github.com/discourse/discourse/commit/6e7a181909c34a059d2b0a6291335a363205b787
github_commit

commit 24cd7cc4c868 (discourse/discourse)

Fix landed in discourse/discourse commit 24cd7cc4c868 — awaiting tagged release

https://github.com/discourse/discourse/commit/24cd7cc4c868f20e6037d67d801d60c3e289b278
github_pr

Security fixes for main

Fix merged in discourse/discourse PR #42882 on 2026-08-25 — awaiting tagged release

https://github.com/discourse/discourse/pull/42882
github Patch Available

Chat upload filenames rendered as raw HTML in excerpts · Advisory · discourse/discourse · GitHub

https://github.com/discourse/discourse/security/advisories/GHSA-34rh-wjfv-65gq

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 4× in last 7d / 4× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-09-24 18:35 UTCEG score recompute
  2. 2026-09-24 17:37 UTCEG score recompute
  3. 2026-09-24 17:18 UTCEG score recompute
  4. 2026-09-24 17:17 UTCMITRE cvelistV5first tracked

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Frequently asked(4)

What is CVE-2026-91121?
CVE-2026-91121 is a medium vulnerability published on September 24, 2026. 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…
When was CVE-2026-91121 disclosed?
CVE-2026-91121 was first published in the National Vulnerability Database on September 24, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
What is the CVSS score of CVE-2026-91121?
CVE-2026-91121 has a CVSS v3 base score of 5.0 (NVD). The EG score is currently aggregating — additional source signals are being incorporated as they become available..
How do I remediate CVE-2026-91121?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-91121, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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