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CVE-2026-55229 – Blind SSRF & Local File Disclosure – Gotenberg prior to 8.34.0

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Summary

CVE-2026-55229 is a Server-Side Request Forgery (SSRF) vulnerability rated High severity (CVSS 7.5) affecting Gotenberg, a Docker-powered stateless HTTP API for converting documents to PDF. The flaw exists in the /forms/libreoffice/convert endpoint, where a specially crafted document causes LibreOffice to automatically retrieve external HTTP(S) resources and local filesystem resources during conversion, enabling blind SSRF and limited local file disclosure. The vulnerability is fixed in Gotenberg version 8.34.0.

Technical details

  • Root cause: The /forms/libreoffice/convert endpoint passes uploaded documents (e.g., DOCX, ODT, RTF) directly to LibreOffice for conversion without sufficiently restricting linked resource resolution. LibreOffice automatically fetches external URLs and local file:// paths embedded as image sources within the document, without adequate security controls.
  • Trigger condition: An unauthenticated attacker uploads a specially crafted document containing embedded references to external HTTP(S) URLs or local filesystem paths as image sources.
  • Attack vector: Remote, unauthenticated, over the network. No user interaction is required. Gotenberg provides no built-in authentication by default, meaning any caller who can reach the endpoint can submit a malicious document.
  • Impact – Blind SSRF: LibreOffice issues outbound HTTP(S) requests to attacker-controlled or internal destinations during conversion, enabling probing and interaction with internal services that rely on network-level trust assumptions (e.g., cloud metadata endpoints, internal APIs).
  • Impact – Local file disclosure: By referencing local filesystem paths as image sources, LibreOffice attempts to load and embed the referenced resources into the output document, enabling limited disclosure of files accessible to the LibreOffice process.
  • CWE: CWE-918 – Server-Side Request Forgery (SSRF)

Affected software

  • Gotenberg all versions prior to 8.34.0

Severity

  • CVSS v3.1 Base Score: 7.5 (HIGH)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

Mitigation and recommended actions

  • Immediate: Upgrade Gotenberg to version 8.34.0 or later. Version 8.34.0 implements LibreOffice profile settings that block the loading of untrusted linked content during document conversion, preventing externally or locally referenced resources from being resolved.
  • Network mitigation (if immediate patching is not possible): Restrict network access to the Gotenberg instance so that it is not reachable from untrusted or public networks. Place Gotenberg behind an authenticated reverse proxy or API gateway, and enforce egress filtering to prevent outbound connections from the LibreOffice conversion process to internal infrastructure or the internet.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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