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Fencer Intel
high 7.2

CVE-2026-91123 json

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

published 2mo ago modified last mo. also BIT-discourse-2026-91123 , EUVD-2026-86300 , GHSA-6pwj-wgg8-4rjc

cvss
7.2
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 21%
public exploits
0
none known

Summary

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.

Patch / fix

  • bitnami discourse 2026.8.0
  • discourse discourse 2026.1.8, 2026.6.3, 2026.7.2, 2026.8.0

Is CVE-2026-91123 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
last mo.

Exploit prediction

0.29% chance of exploitation in the next 30 days, higher than 21% of all scored CVEs (FIRST EPSS, 2026-11-11).

CVSS scores

assigned by version score vector
CNA 3.1 7.2 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
OSV 3.1 7.2 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N

Affected packages

ecosystem package affected fixed in
bitnami discourse
<2026.8.0
2026.8.0

Affected products

  • discourse discourse

Classification

Weakness
  • CWE-22 Improper Limitation of a Pathname to a Restricted Directory

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

The maintainers of discourse/discourse published their own advisory on GitHub. Reviewed sources take precedence over it.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.