What is CVE-2026-55420?
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.
The record classifies CVE-2026-55420 under weakness class CWE-78. Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs low-privilege credentials, needs no user interaction, and has high impact on confidentiality, integrity, availability. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 95 days ago.
Severity and exploitation probability
- CVSS v3.1 base score
- 7.5 — HIGH
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H - EPSS (FIRST)
- 0.6% probability of exploitation in the next 30 days, higher than 47.3% of all scored CVEs
- CISA KEV
- Not listed in the CISA Known Exploited Vulnerabilities catalog
- Threadlinqs priority
- 5.6/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- Published
- 2026-07-09, last modified 2026-07-14
Is CVE-2026-55420 being exploited?
It currently carries a trending score of 23 in the Threadlinqs vulnerability feed.
Affected products and versions
- discourse: discourse
How to fix CVE-2026-55420
The record marks a vendor fix as available for CVE-2026-55420. Patch reference: https://github.com/discourse/discourse/commit/ca5a7e06167561928556afa2f237d67e459c6914. Vendor advisory: https://github.com/discourse/discourse/security/advisories/GHSA-7wq5-jgww-5rw3. Apply the vendor fix referenced above to every affected product listed in this record, then confirm the running version against the vendor advisory.
Threat activity tracking CVE-2026-55420
No threat campaign in the Threadlinqs corpus currently references CVE-2026-55420, in its CVE list or as an indicator. The linkage is recomputed from the live corpus on every daily ingest, so this section fills in as soon as a tracked campaign cites the identifier.
Sources
Enriched from CVE.org, NVD, FIRST EPSS. Last verified by Threadlinqs on . This product uses the NVD API but is not endorsed or certified by the NVD.