CVE-2026-91159Public exploitNetwork attack vectorHinoki check available

Stored HTML injection via overtrusted oEmbed fragments

Published Oct 14, 2026 · Updated Oct 14, 2026

HTML injection in Discourse oEmbed processing allows remote authenticated users to insert misleading interfaces via posted URLs. The processor trusts an entire attacker-controlled HTML fragment when its first iframe matches the configured source allowlist, admitting unrelated sibling HTML and CSS. Exploitation requires posting permission and control of a public webpage and its oEmbed response; injected overlays affect content integrity without exposing restricted data or disrupting service.

CVSS severity7.7
High
EPSS probability0.43%
Next 30 days · Oct 19, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

HTML injection in Discourse oEmbed processing allows remote authenticated users to insert misleading interfaces via posted URLs. The processor trusts an entire attacker-controlled HTML fragment when its first iframe matches the configured source allowlist, admitting unrelated sibling HTML and CSS. Exploitation requires posting permission and control of a public webpage and its oEmbed response; injected overlays affect content integrity without exposing restricted data or disrupting service.

The record

CVE
CVE-2026-91159
Published
Oct 14, 2026
Updated
Oct 14, 2026
Vendor
Discourse
Product
Discourse
Classifications
T1565.001
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Oct 14, 2026CVE publishedPublication date reported by the CVE source.
  2. Oct 14, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 2026.1.9
  2. Affected versionversion=>= 2026.7.0-latest, < 2026.7.3
  3. Affected versionversion=>= 2026.8.0-latest, < 2026.8.1
  4. Affected versionversion=>= 2026.9.0-latest, < 2026.9.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Discourse · Discourseversion=< 2026.1.9; version=>= 2026.7.0-latest, < 2026.7.3; version=>= 2026.8.0-latest, < 2026.8.1; version=>= 2026.9.0-latest, < 2026.9.0

Published CVSS scores

7.7DiscourseCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Activity data is delayed. The latest report is Sep 28, 2026.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 22, 2026Sep 28, 2026
Latest reporting daySep 28, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

T1565.001Stored Data Manipulation

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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