Analyst readout for executives and security teams
Plain-English summary
CVE-2026-9558 is a critical flaw in Mautic's theme system. A logged-in user who can create or upload themes could use a malicious Twig template to run code on the server or read sensitive files. This is serious because marketing platforms often hold credentials, customer data, and integrations.
Executive priority
Treat this as urgent for any internet-facing or multi-user Mautic deployment. The business risk is server compromise and exposure of marketing data, credentials, or connected systems. Prioritize permission restriction immediately while confirming vendor remediation guidance.
Technical view
The source describes a CWE-1336 Server-Side Template Injection in mautic/core. Uploaded Twig templates are rendered without sandboxing or strict function restrictions. With theme creation or upload permission, an authenticated user can potentially achieve remote code execution or access restricted configuration and system files.
Likely exposure
Exposure is likely limited to Mautic deployments where authenticated users can create or upload themes. The affected list names mautic/core versions 1.3.0, 5.0.0, 6.0.0, and 7.0.0, but source evidence should be checked against the GitHub advisory.
Exploitation context
The CVE has a 9.9 CVSS score with network attack vector, low complexity, low privileges, and no user interaction. The bundle marks KEV as false, and the provided sources do not state active exploitation. Exploitation requires a valid account with theme-related permissions.
Researcher notes
Evidence is strong for the vulnerability class and impact, but the provided bundle does not include fixed versions or detailed vendor mitigation text. Avoid assuming broad unauthenticated exposure; the stated prerequisite is authenticated theme creation or upload permission.
Mitigation direction
- Review the GitHub advisory and apply any vendor-published patched version when available.
- Restrict theme creation and upload permissions to trusted administrators only.
- Disable theme uploads temporarily if they are not operationally required.
- Review recent theme changes and investigate unexpected uploads or template edits.
- Rotate secrets if investigation suggests configuration files were accessed.
Validation and detection
- Inventory Mautic deployments and record mautic/core versions.
- Identify accounts and roles with theme creation or upload permissions.
- Review application logs for unexpected theme uploads or template changes.
- Check hosting logs for suspicious activity around theme rendering.
- Verify remediation against the official Mautic advisory before closure.
Public sources used
Based on public source material and reviewed before publication.
Conservative CVE-to-ATT&CK context
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ATT&CK lookup starting points
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CWE-1336: Exact CWE lookup
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Open ATT&CK lookupExecution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2026-9558 mapping review
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Open ATT&CK lookup- Severity
- Critical
- CVSS
- 9.9 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H 3.1 6 Mautic Vulnerability scoring details
Base CVSS 3.1 score
9.9 CriticalVector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reserved CVE Program
The CVE ID was reserved by the assigning CNA.
- CVE published CVE Program
The CVE record was published.
- CVE updated CVE Program
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Source materials
- CVE List V5 source CVE List V5
- https://github.com/mautic/mautic/security/advisories/GHSA-9fx4-7cmj-47vg CVE reference, Mautic
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
CWE mapping pending import
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