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Discourse: Stored oEmbed HTML injection via allowed iframe

Type: advisorySource: Official CVE List1 source record

Discourse is an open-source discussion platform. Prior to 2026.9.0, 2026.8.1, 2026.7.3, and 2026.1.9, oEmbed processing treated an entire attacker-controlled HTML fragment as trusted when the fragment contained an iframe whose source matched the configured allowlist. A user with posting permission who controlled a public webpage and its oEmbed response could combine an allowlisted iframe with unrelated sibling HTML or CSS, causing stored visual overlays or other styled content to appear in post content and enabling misleading or fraudulent user interfaces. Exploitation requires a posting account, control of the fetched webpage and oEmbed response, and an allowlisted iframe source. The issue affects content integrity but does not expose restricted data, disrupt availability, or require interaction with Discourse Content Security Policy. This issue is fixed in versions 2026.9.0, 2026.8.1, 2026.7.3, and 2026.1.9.

Announced Source revision 1
Original source ↗

CVE-2026-91159

Primary source · Revision 1

Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.

Security context

Source reference: cve:CVE-2026-91159

discourse

Source reference: /containers/cna/affected/0/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

Structured affected-version data

Original package identities and version rules from this source.

[
  {
    "vendor": "discourse",
    "product": "discourse",
    "versions": [
      {
        "status": "affected",
        "version": "< 2026.1.9"
      },
      {
        "status": "affected",
        "version": ">= 2026.7.0-latest, < 2026.7.3"
      },
      {
        "status": "affected",
        "version": ">= 2026.8.0-latest, < 2026.8.1"
      },
      {
        "status": "affected",
        "version": ">= 2026.9.0-latest, < 2026.9.0"
      }
    ]
  }
]
Related CVEs
CVE-2026-91159

Source reference: /cveMetadata/cveId

Publisher severity

high

Source reference: /containers/cna/metrics

Event
#42065 · Revision 1
Added to Heist Feed
Publisher date
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