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CVE-2026-91123— Discourse: Reject literal backslash path separators in iframe src traversal guard

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，iframe 源（src）遍历保护机制在解码点段（dot segments）后，未将字面量反斜杠（literal backslashes）视为路径分隔符。因此，精心构造的 src 值可以通过 allowed_iframes 子路径检查，而浏览器在进行 URL 规范化时会将 iframe 移出预期的允许路径。结果可能导致 iframe 加载管理员未授权的内容。该问题已在版本 2026.1

CVSS 7.2 · High EPSS 0.29% · P19
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I. Basic Information for CVE-2026-91123

Vulnerability Information
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Vulnerability Title
Discourse: Reject literal backslash path separators in iframe src traversal guard
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, the iframe src traversal guard did not treat literal backslashes as path separators after decoded dot segments. A crafted source could therefore pass an allowed_iframes subpath check while browser URL normalization moved the iframe outside the intended allowed path. The resulting iframe could load content from a location that the administrator did not allow. 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:N/UI:N/S:C/C:L/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
对路径名的限制不恰当(路径遍历)
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
discourse discourse < 2026.8.0 -

II. Public POCs for CVE-2026-91123

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III. Intelligence Information for CVE-2026-91123

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Other References for CVE-2026-91123 (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-2026-91133 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-2026-91121 5.0 MEDIUM Discourse: Chat upload filenames rendered as raw HTML in excerpts
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-22

V. Comments for CVE-2026-91123

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