What is the CVSS score of CVE-2026-55420?

CVE-2026-55420 has a CVSS 3.1 base score of 8.1 (High). CVSS vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H. EPSS exploitation probability: 0.3%.

Which versions of Discourse are affected by CVE-2026-55420?

Discourse's discourse-ai plugin contains a remote code execution vulnerability (CVE-2026-55420, CVSS 8.1) in its PDF processing feature that allows attackers uploading crafted PDFs to execute…. A patch is available.

How to fix or mitigate CVE-2026-55420?

Within 24 hours, inventory all Discourse deployments and determine whether the discourse-ai plugin's LLM vision model features are currently enabled; if enabled, prioritize patching immediately per vendor advisory. Within 7 days, deploy the available vendor patch across all affected Discourse instances running discourse-ai. Within 30 days, complete patch validation on all systems, restrict PDF upload capabilities to authenticated users where operationally feasible, and review PDF upload logs since the vulnerability discovery date for suspicious activity.

Discourse CVE-2026-55420

EUVD-2026-42665 HIGH

OS Command Injection (CWE-78)

2026-07-09 security-advisories@github.com

Command Injection Discourse

8.1

CVSS 3.1 · NVD

Severity by source

Vendor (github) PRIMARY

HIGH

qualitative

NVD

8.1 HIGH

AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

vuln.today AI

7.5 HIGH

Network-delivered upload (AV:N) but requires the non-default discourse-ai PDF/vision config (AC:H) and normally a logged-in uploader (PR:L); delegate RCE yields full host impact (C/I/A:H).

3.1 AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H

4.0 AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Primary rating from Vendor (github).

CVSS VectorNVD

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H

Attack Vector

Network

Attack Complexity

High

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Lifecycle Timeline

Analysis Updated

Jul 13, 2026 - 14:45 vuln.today

v3 (cvss_changed)

Source Code Evidence Fetched

Jul 13, 2026 - 14:45 vuln.today

Analysis Updated

Jul 13, 2026 - 14:45 vuln.today

v2 (cvss_changed)

Re-analysis Queued

Jul 13, 2026 - 14:37 vuln.today

cvss_changed

CVSS changed

Jul 13, 2026 - 14:37 NVD

7.5 (HIGH) 8.1 (HIGH)

Patch available

Jul 09, 2026 - 19:01 EUVD

Analysis Generated

Jul 09, 2026 - 18:31 vuln.today

DescriptionNVD

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.

AnalysisAI

Remote code execution in Discourse (via the discourse-ai plugin's PDF-to-text feature) allows an attacker who can upload a crafted PDF to run arbitrary commands on the server, but only in non-default configurations where an LLM vision model is configured. The flaw is a CWE-78 OS command injection reached when uploaded PDFs are rasterized through ImageMagick, which in turn invokes an external delegate (Ghostscript) on attacker-controlled input. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access

Authenticate and gain upload rights

Delivery

Upload crafted PDF with PostScript payload

Exploit

discourse-ai rasterizes PDF via ImageMagick

Execution

ImageMagick invokes Ghostscript delegate on payload

Persist

Shell commands execute

Impact

RCE as Discourse server process

Access

Authenticate and gain upload rights

Delivery

Upload crafted PDF with PostScript payload

Exploit

discourse-ai rasterizes PDF via ImageMagick

Execution

ImageMagick invokes Ghostscript delegate on payload

Persist

Shell commands execute

Impact

RCE as Discourse server process

Vulnerability AssessmentAI

Exploitation	Exploitation requires a non-default deployment: the discourse-ai plugin must be installed and enabled with an LLM/vision model configured, since the vulnerable ImageMagick rasterization branch in pdf_to_text.rb only runs when @llm_model is set - plain instances that only extract PDF text never reach it. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment	Signals are mixed and point to a real-but-conditional risk rather than a mass-exploitation event. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario	On a Discourse instance running discourse-ai with a configured LLM vision model, an attacker with upload rights posts a specially crafted PDF; when the AI pipeline rasterizes it via ImageMagick, the embedded PostScript/delegate payload executes shell commands on the server, giving code execution as the Discourse process. No public exploit is identified at time of analysis, though the ImageMagick/Ghostscript delegate technique is well documented; AC:H reflects that the target must have the non-default AI PDF configuration enabled.
Remediation	Vendor-released patch: upgrade to 2026.6.0, 2026.5.1, 2026.4.2, or 2026.1.5 (whichever matches your release train), per advisory GHSA-7wq5-jgww-5rw3 and the release tags at https://github.com/discourse/discourse/releases; the underlying change is commit ca5a7e06167561928556afa2f237d67e459c6914. … Detailed patch versions, workarounds, and compensating controls in full report.

Recommended ActionAI

Within 24 hours, inventory all Discourse deployments and determine whether the discourse-ai plugin's LLM vision model features are currently enabled; if enabled, prioritize patching immediately per vendor advisory. …

Threat intelligence, references, and detailed analysis are available after sign-in.