Is CVE-2026-91134 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-91134 being exploited in the wild.

How severe is CVE-2026-91134?

Medium severity, with a CVSS score of 5.4, published 24 September 2026.

Which products and versions are affected?

Discourse Prior to 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0.

Is there a fix for CVE-2026-91134?

A patch was published on 2026-01-08: Fixed in Discourse 2026.1.8 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-91134 attacked?

It is attacked over the network, in a web application.

Am I affected by CVE-2026-91134?

Check whether you run Discourse at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-91134: Discourse post sanitizer iframe bypass via encoded userinfo

CVE-2026-91134 · Severity: medium · CVSS 5.4 · Published 2026-09-24

Discourse, a popular community discussion platform, contains a vulnerability in how it filters embedded content (iframes) in user posts. An attacker with posting privileges can embed malicious cross-origin content that appears safe to the content filter by encoding the URL in a specific way, allowing attacker-controlled websites to load within trusted pages. This could lead to data theft, session hijacking, or malware distribution to community members.

Technologies: Discourse. Vendors: Discourse.

Quick answers

Is CVE-2026-91134 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-91134 being exploited in the wild.
How severe is CVE-2026-91134?: Medium severity, with a CVSS score of 5.4, published 24 September 2026.
Which products and versions are affected?: Discourse Prior to 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0.
Is there a fix for CVE-2026-91134?: A patch was published on 2026-01-08: Fixed in Discourse 2026.1.8 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-91134 attacked?: It is attacked over the network, in a web application.
Am I affected by CVE-2026-91134?: Check whether you run Discourse at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

The post sanitizer validates iframe URLs inconsistently: it checks an encoded form against an allowlist prefix policy but the browser interprets a decoded form, creating a mismatch that allows bypassing the allowed_iframes allowlist. An authenticated user with posting privileges can persist a crafted iframe in a post, causing the browser to render attacker-controlled cross-origin content. The vulnerability exists in the sanitizer.js component and is fixed by properly validating URLs in their final decoded form before comparing against security policies.

Affected products

Discourse Discourse Prior to 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0

Timeline

2026-09-24: disclosed: CVE-2026-91134 published
2026-01-08: patched: Fixed in Discourse 2026.1.8
2026-06-03: patched: Fixed in Discourse 2026.6.3
2026-07-02: patched: Fixed in Discourse 2026.7.2
2026-08-00: patched: Fixed in Discourse 2026.8.0

References

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