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Fencer Vulns
high 7.7

CVE-2026-91159 json

Discourse: Stored oEmbed HTML injection via allowed iframe

published 2026-10-14 26 d ago modified 2026-10-21 19 d ago also BIT-discourse-2026-91159 , EUVD-2026-101299 , GHSA-f9jx-vv33-4282

cvss
7.7
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 36%
public exploits
0
none known

Summary

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.

Patch / fix

  • bitnami discourse 2026.1.9, 2026.7.3, 2026.8.1, 2026.9.0
  • discourse discourse 2026.1.9, 2026.7.3, 2026.8.1, 2026.9.0

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
20 d ago

Exploit prediction

0.42% chance of exploitation in the next 30 days, higher than 36% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.7 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:N
OSV 3.1 7.7 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:N

Affected packages

ecosystem package affected fixed in
bitnami discourse
<2026.1.9
>=2026.7.0, <2026.7.3
>=2026.8.0, <2026.8.1
>=2026.8.99, <2026.9.0
2026.1.9
2026.7.3
2026.8.1
2026.9.0

Affected products

  • discourse discourse

Classification

Weakness
  • CWE-79 Improper Neutralization of Input During Web Page Generation

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.