Discourse is an open-source discussion platform. Prior to 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0, the Discourse post sanitizer allowed a stored cross-origin iframe to bypass the allowed_iframes prefix policy when the iframe src contained encoded userinfo. The sanitizer validated a decoded form differently from the stored iframe src, allowing the browser to interpret an attacker-controlled host while the allowlist check accepted the encoded URL as an allowed prefix. An authenticated user with posting privileges could persist the iframe in a post and cause attacker-controlled cross-origin content to be rendered. This issue is fixed in versions 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0.
CVE-2026-91134
MEDIUMPre-NVD 5.45.4
EchelonGraph scoreLOW confidence
This medium-severity CVE scores 5.4 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
5.4EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
- Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: —CVSS: 5.4Exploit: None knownExposed: 0
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- CVSS v3
- 5.4
- EG Score
- 5.4(low)
- EG Risk
- 29(Track)EG Risk 29/100SSVC: 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 computedSeverity54% × 45%Exploitation0% × 40%Automatability30% × 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, 2026Patch available. Sources: github, github_pr, github_commit.
github_commit
commit fed3a58c4841 (discourse/discourse)
Fix landed in discourse/discourse commit fed3a58c4841 — awaiting tagged release
https://github.com/discourse/discourse/commit/fed3a58c48412ce7207b72a4629ddbc44482cd64github_commit
commit bac7dd120191 (discourse/discourse)
Fix landed in discourse/discourse commit bac7dd120191 — awaiting tagged release
https://github.com/discourse/discourse/commit/bac7dd1201911851462483271b4567246fa1309dgithub_commit
commit 1304b0c04f87 (discourse/discourse)
Fix landed in discourse/discourse commit 1304b0c04f87 — awaiting tagged release
https://github.com/discourse/discourse/commit/1304b0c04f87534053b0d574ae5a9b9ba13dd590github_commit
commit 0a8015e6c7a5 (discourse/discourse)
Fix landed in discourse/discourse commit 0a8015e6c7a5 — awaiting tagged release
https://github.com/discourse/discourse/commit/0a8015e6c7a5079981843721494d30c9a91f5415github_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/42882github Patch Available
Block post iframes whose encoded userinfo bypasses the allowed_iframes allowlist · Advisory · discourse/discourse · GitHub
https://github.com/discourse/discourse/security/advisories/GHSA-54vw-chv3-wjpvWeakness Classification(1)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 3× in last 7d / 3× 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.
- 2026-09-24 17:33 UTCEG score recompute
- 2026-09-24 16:57 UTCEG score recompute
- 2026-09-24 16:56 UTCMITRE cvelistV5first tracked
Related CVEs(same CWE)
Frequently asked(4)
What is CVE-2026-91134?
CVE-2026-91134 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, the Discourse post sanitizer allowed a stored cross-origin iframe to bypass the allowed_iframes prefix policy when the iframe src contained encoded userinfo. The sanitizer validated a decoded form…
When was CVE-2026-91134 disclosed?
CVE-2026-91134 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-2026-91134?
CVE-2026-91134 has a CVSS v3 base score of 5.4 (NVD). The EG score is currently aggregating — additional source signals are being incorporated as they become available..
How do I remediate CVE-2026-91134?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-91134, 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.
Dependency Blast Radius
Explore the affected products and dependency analysis for CVE-2026-91134
Is Your Infrastructure Affected by CVE-2026-91134?
EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.