Review reviewHigh

CVE-2026-55420

discourse

Discourse is an open-source discussion platform. Prior to 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5, under certain non-default configurations, processing of PDF uploads could be exploited to obtain RCE on the server. This issue is patched in 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5.

CVSS
8.1
EPSS
0.35%
27.4% percentile
CISA KEV
Not listed
Published
2026.07.10
PRIORITY ASSESSMENT

Review review

The CVSS severity warrants an early asset and exposure review.

Known exploitationNot established by KEV
Exploit probability0.35%
Technical severityCVSS 8.1

Vulnerability overview

Discourse is an open-source discussion platform. Prior to 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5, under certain non-default configurations, processing of PDF uploads could be exploited to obtain RCE on the server. This issue is patched in 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5.

Affected product and versions

Product
discourse
Affected versions
>= >= 2026.5.0-latest, < 2026.5.1, >= >= 2026.4.0-latest, < 2026.4.2, >= >= 2026.1.0-latest, < 2026.1.5, >= 2026.1.0 < 2026.1.5, >= 2026.4.0 < 2026.4.2, >= 2026.5.0 < 2026.5.1, 2026.6.0
Fixed versions
2026.1.5, 2026.4.2, 2026.5.1

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide
  1. 1
    Identify

    Confirm that discourse and an affected version are present.

  2. 2
    Prioritize

    Combine exploitation signals with asset exposure and business criticality.

  3. 3
    Remediate

    Follow the vendor advisory or supported update path and preserve rollback options.

  4. 4
    Verify

    Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
CWE
CWE-78