# CVE-2026-55420: Discourse RCE via PDF upload processing

Source: https://junglewise.ai/threats/cve-2026-55420-discourse-rce-via-pdf-upload-processing  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-09. Updated: 2026-07-09  
License: CC BY 4.0 with a link back

CVE-2026-55420 · Severity: high · CVSS 7.5 · Published 2026-07-09

Discourse, a popular open-source discussion and forum platform, is vulnerable to a security flaw that allows attackers to take control of the server. By uploading a specially crafted PDF file, an attacker can execute malicious commands on the underlying system. This could lead to a total compromise of the forum, including the theft of user data or a complete service shutdown. The vulnerability only affects systems with specific non-default configurations.

Technologies: [Discourse](https://junglewise.ai/threats/technologies/discourse). Vendors: [Discourse](https://junglewise.ai/threats/vendors/discourse).

## Quick answers

**Is CVE-2026-55420 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-55420 being exploited in the wild.

**How severe is CVE-2026-55420?** High severity, with a CVSS score of 7.5, published 9 July 2026.

**Which products and versions are affected?** Discourse < 2026.1.5, < 2026.4.2, < 2026.5.1, < 2026.6.0.

**Is there a fix for CVE-2026-55420?** A patch was published on 2026-06-30: Security hardening commit and releases published. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-55420 attacked?** It is attacked over the network, in a network appliance.

**Am I affected by CVE-2026-55420?** Check whether you run Discourse at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

Discourse is vulnerable to an OS command injection (CWE-78) vulnerability during the processing of PDF uploads. The issue stems from insufficient neutralization of special elements when shelling out to ImageMagick or Ghostscript for PDF-to-image processing. An authenticated attacker with network access can exploit this by uploading a malicious PDF, provided the forum is using a non-default configuration that enables PDF processing. Successful exploitation results in Remote Code Execution (RCE) with the privileges of the Discourse application. The fix involves hardening ImageMagick execution by implementing a default-deny security policy and removing experimental PDF-to-image logic. Patches are available in versions 2026.6.0, 2026.5.1, 2026.4.2, and 2026.1.5.

## Affected products

- Discourse Discourse < 2026.1.5, < 2026.4.2, < 2026.5.1, < 2026.6.0

## Timeline

- 2026-06-30: patched: Security hardening commit and releases published.
- 2026-07-09: disclosed: CVE-2026-55420 published.

## References

- [https://github.com/discourse/discourse/commit/ca5a7e06167561928556afa2f237d67e459c6914](https://github.com/discourse/discourse/commit/ca5a7e06167561928556afa2f237d67e459c6914)
- [https://github.com/discourse/discourse/releases/tag/v2026.1.5](https://github.com/discourse/discourse/releases/tag/v2026.1.5)
- [https://github.com/discourse/discourse/releases/tag/v2026.4.2](https://github.com/discourse/discourse/releases/tag/v2026.4.2)
- [https://github.com/discourse/discourse/releases/tag/v2026.5.1](https://github.com/discourse/discourse/releases/tag/v2026.5.1)
- [https://github.com/discourse/discourse/releases/tag/v2026.6.0](https://github.com/discourse/discourse/releases/tag/v2026.6.0)
- [https://github.com/discourse/discourse/security/advisories/GHSA-7wq5-jgww-5rw3](https://github.com/discourse/discourse/security/advisories/GHSA-7wq5-jgww-5rw3)

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- [Discourse oEmbed HTML injection in iframe allowlist](https://junglewise.ai/threats/cve-2026-91159-discourse-is-an-open-source-discussion-platform-prior-to-2026-9-0)
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- [Discourse HTML injection in chat message excerpts](https://junglewise.ai/threats/cve-2026-91121-discourse-is-an-open-source-discussion-platform-prior-to-2026-1-8)
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