CVE-2025-55161
Published: 11 August 2025
Summary
CVE-2025-55161 is a high-severity SSRF (CWE-918) vulnerability in Stirlingpdf Stirling Pdf. Its CVSS base score is 8.6 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploit Public-Facing Application (T1190); ranked in the top 7.5% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified are NIST 800-53 AC-4 (Information Flow Enforcement) and SC-7 (Boundary Protection).
Deeper analysis
Stirling-PDF is a locally hosted web application for performing operations on PDF files. Prior to version 1.1.0, the /api/v1/convert/markdown/pdf endpoint invokes a third-party tool to convert Markdown input to PDF and applies a security sanitizer that can be bypassed, resulting in server-side request forgery (SSRF) classified under CWE-918. The flaw affects unauthenticated network requests to this endpoint and carries a CVSS 3.1 score of 8.6.
An attacker with network access can submit specially crafted Markdown payloads to the conversion endpoint, bypassing the sanitizer to force the application into making arbitrary requests to internal or external resources. This enables high-impact confidentiality exposure along with limited integrity and availability effects without requiring user interaction or credentials.
The project has released version 1.1.0 to address the issue, with the fix documented in commit 7d6b70871bad2a3ff810825f7382c49f55293943 and the GitHub Security Advisory GHSA-ff33-grr6-rmvp. The associated EPSS score remains at 0.0836 with no material increase from its peak value.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2025-24184
Vulnerability details
Stirling-PDF is a locally hosted web application that performs various operations on PDF files. Prior to version 1.1.0, when using the /api/v1/convert/markdown/pdf endpoint to convert Markdown to PDF, the backend calls a third-party tool to process it and includes a…
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sanitizer for security sanitization which can be bypassed and result in SSRF. This issue has been patched in version 1.1.0.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
SSRF in public-facing web API (/api/v1/convert/markdown/pdf) enables exploitation (T1190), local data access via localhost requests (T1005), and internal network service/port discovery (T1046) by fetching arbitrary URLs during Markdown-to-PDF conversion.
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Directly addresses the SSRF vulnerability by requiring validation of Markdown inputs to prevent sanitizer bypasses that enable unauthorized backend requests.
Boundary protection restricts outbound network communications from the Stirling-PDF server, blocking forged requests to internal or external resources.
Enforces information flow control policies to limit server-initiated requests during Markdown-to-PDF processing to only approved destinations.