What’s Vulnerable › Vulnerabilities

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

• Severity: medium (CVSS 6.4 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-24 · updated 2026-09-28
• Weakness: CWE-79

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.

Affected products

• discourse: before 2026.8.0; from 2026.7.0-latest, < 2026.7.2; from 2026.6.0-latest, < 2026.6.3; from 2026.1.0-latest, < 2026.1.8

References

• https://github.com/discourse/discourse/commit/20dbf112760eb1d6a58f2e49aeef7546898b6f1c
• https://github.com/discourse/discourse/commit/66653c484cfb91bc346f9a326f6945387f17b035
• https://github.com/discourse/discourse/commit/77a81c7a3a7ff9e94b355e32b8f379f2d389e05a
• https://github.com/discourse/discourse/commit/c4748f651d9d2f3a6dd3106a4d5564536c645168
• https://github.com/discourse/discourse/pull/42882
• https://github.com/discourse/discourse/security/advisories/GHSA-pv3p-p3m9-v8v3

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