CVE-2026-91119: Discourse: Encode action_code_who in mention URLs

Description

Discourse is an open-source discussion platform. Prior to 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0, the topic small-action and nested-activity-log components interpolated the free-form action_code_who value into mention-link href attributes without URL encoding. A quote-bearing display name could terminate the intended URL attribute and inject attacker-controlled elements into the trusted rendered markup. Although the visible mention text was escaped, the unencoded path component allowed stored HTML injection when another user viewed the affected topic action or activity log. This issue is fixed in versions 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0.

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N

Attack vector

Network

Complexity

Low

Privileges

Low

User interaction

None

Confidentiality

Low

Integrity

Low

Availability

None

Scope

Changed

Exploitation

Is it being used?

Exploit prediction (EPSS)0.2% · higher than 10% of CVEs

Exploited in the wildNo evidence yet

CISA KEVNot listed

Ransomware campaign useNot known

Affected products

Which versions

DI

discourse · discourse

< 2026.8.0; >= 2026.7.0-latest, < 2026.7.2; >= 2026.6.0-latest, < 2026.6.3; >= 2026.1.0-latest, < 2026.1.8 · source: vendor