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CVE-2026-91121— Discourse: Chat upload filenames rendered as raw HTML in excerpts

Quick assessment

Affected
discourse discourse
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Discourse 是一个开源的讨论平台。在 2026.1.8、2026.6.3、2026.7.2 和 2026.8.0 版本之前，攻击者控制的上传文件名在聊天消息摘录中被作为未转义的 HTML 渲染。能够上传文件并发送聊天内容的用户，可以在文件名中植入标记，这些标记随后会被聊天频道列表、聊天摘要邮件、固定消息栏、回复预览、线程预览以及其他摘录渲染器解析并显示。该漏洞允许注入受信任的 HTML，从而改变已渲染摘录的内容，但在默认的内容安全策略（CSP）设置下，未验证 JavaScript 的执行。官方公告指出，未发

CVSS 5.0 · Medium EPSS 0.26% · P16
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I. Basic Information for CVE-2026-91121

Vulnerability Information
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Vulnerability Title
Discourse: Chat upload filenames rendered as raw HTML in excerpts
Source: CVE Program / CVE List V5
Vulnerability Description
Discourse is an open-source discussion platform. Prior to 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0, attacker-controlled upload filenames used in chat message excerpts were rendered as unescaped HTML. A user able to upload a file and send chat content could place markup in a filename that was then interpreted by chat channel lists, chat summary emails, pinned message bars, reply previews, thread previews, and other excerpt renderers. The issue allowed trusted-HTML injection that altered rendered excerpt content, but JavaScript execution was not demonstrated with default Content Security Policy settings. The advisory states that no confidentiality, integrity, or availability impact was identified, while its structured scoring metadata separately assigns low integrity impact. Sites that disable or relax the default CSP have increased exposure. This issue is fixed in versions 2026.1.8, 2026.6.3, 2026.7.2, and 2026.8.0.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
在Web页面生成时对输入的转义处理不恰当(跨站脚本)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
discourse discourse < 2026.8.0 -

II. Public POCs for CVE-2026-91121

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III. Intelligence Information for CVE-2026-91121

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Other References for CVE-2026-91121 (6)

Same Patch Batch · discourse · 2026-09-24 · 9 CVEs total

CVE-2026-91122 8.7 HIGH Discourse: Chat MessageBus delivers read-restricted messages to unauthorized users
CVE-2026-91123 7.2 HIGH Discourse: Reject literal backslash path separators in iframe src traversal guard
CVE-2026-91133 6.5 MEDIUM Discourse: Escape LIKE metacharacters in upload paths to prevent disclosure
CVE-2026-91119 6.4 MEDIUM Discourse: Encode action_code_who in mention URLs
CVE-2026-91134 5.4 MEDIUM Discourse: Block post iframes whose encoded userinfo bypasses the allowed_iframes allowlis
CVE-2026-91120 5.4 MEDIUM Discourse: Stored HTML injection in video notification emails
CVE-2026-91132 4.3 MEDIUM Discourse: Wildcard iframe origin allowlist bypass via authority separators
CVE-2026-84302 4.2 MEDIUM Discourse: Non-participant moderators can read, edit, and delete PM content through Discou

IV. Related Vulnerabilities

Same product: discourse
Same vendor: discourse
Same weakness: CWE-79

V. Comments for CVE-2026-91121

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