Discourse: Reject literal backslash path separators in iframe src traversal guard

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-91123
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-24 17:17:08 UTC
Updated2026-09-24 18:19:06 UTC
DescriptionDiscourse 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.

Risk And Classification

Primary CVSS: v3.1 7.2 HIGH from [email protected]

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

Problem Types: CWE-22 | CWE-22 CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary7.2HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
3.1CNADECLARED7.2HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
None

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

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Discourse Discourse affected < 2026.8.0 Not specified
CNA Discourse Discourse affected >= 2026.7.0-latest, < 2026.7.2 Not specified
CNA Discourse Discourse affected >= 2026.6.0-latest, < 2026.6.3 Not specified
CNA Discourse Discourse affected >= 2026.1.0-latest, < 2026.1.8 Not specified

References

ReferenceSourceLinkTags
github.com/discourse/discourse/security/advisories/GHSA-6pwj-wgg8-4rjc [email protected] github.com
github.com/discourse/discourse/commit/0b5a27e689925edce9ba9b14110022435d... [email protected] github.com
github.com/discourse/discourse/commit/142f5155ad8e56ddb8012c4e70c69a03de... [email protected] github.com
github.com/discourse/discourse/pull/42882 [email protected] github.com
github.com/discourse/discourse/commit/097ce5600a2d74d9c68e57974597ab2684... [email protected] github.com
github.com/discourse/discourse/commit/042d7b159beda4f74d23e245e8b2e396d9... [email protected] github.com
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