CVE-2026-63270 in LibreOffice
Summary
by MITRE • 10/05/2026
URLs could be constructed which expanded environment variable or INI file values, so potentially sensitive information could be exfiltrated to a remote server on opening a document containing such links. The check added for CVE-2024-12426 did not cover every place a document can supply a URL. XForms instance data and the Calc csv and sql data providers still reached the expansion. In fixed versions these places refuse URLs with internal schemes when the URL comes from the document.
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Analysis
by VulDB Data Team • 10/05/2026
The vulnerability described involves a critical flaw in how certain office suite applications handle Uniform Resource Locators within documents, specifically concerning the expansion of environment variables or INI file values embedded in those links. This issue allows for the construction of URLs that trigger system-level variable substitution when a document containing such maliciously crafted hyperlinks is opened by an unsuspecting user. The core technical flaw lies in the incomplete implementation of security checks introduced to address previous vulnerabilities, specifically CVE-2024-12426. While earlier patches attempted to mitigate risks associated with internal URL schemes, they failed to cover every code path through which a document can supply or define a URL. Consequently, specific components such as XForms instance data and the Calc CSV and SQL data providers remained vulnerable because they continued to process these inputs without adequate sanitization of variable expansions.
From an operational perspective, this flaw enables information disclosure attacks where sensitive system information can be exfiltrated to a remote server controlled by an attacker. The mechanism relies on social engineering or document manipulation to trick the application into resolving internal variables within URLs. When the user opens the compromised document, the application processes the link, expands any embedded environment variable references using local system values, and then attempts to access that expanded URL. If this expansion results in a request directed toward an external domain under attacker control, sensitive data from the victim's machine is transmitted out of the network perimeter. This represents a classic path traversal or server-side request forgery variant where the application acts as an unwitting proxy for exfiltrating local configuration details, user credentials stored in environment variables, or other confidential system parameters.
This vulnerability aligns with CWE-20 Improper Input Validation and CWE-78 OS Command Injection principles, particularly regarding the unsafe interpretation of input data that influences system behavior. In terms of threat modeling, it corresponds to ATT&CK technique T1560 Archive Collected Data followed by T1041 Exfiltration Over C2 Channel, as the attacker collects local information and sends it out via a network connection initiated by the victim's application. The failure to restrict internal schemes in all document-supplied URL contexts highlights a gap in defense-in-depth strategies where security controls are applied inconsistently across different modules of an application suite.
To mitigate this risk, fixed versions of the software have been released that explicitly refuse URLs containing internal schemes when those URLs originate from within the document itself. This restriction ensures that even if environment variables or INI values are present in a link definition, they will not be expanded into potentially dangerous external requests unless the URL is deemed safe by strict protocol validation. Administrators and users should ensure their office suite software is updated to these patched versions immediately. Additionally, organizations should enforce policies that restrict macro execution and discourage opening documents from untrusted sources until all security patches are applied. Monitoring network traffic for unusual outbound connections originating from office applications can also aid in detecting potential exploitation attempts of this vulnerability before significant data loss occurs.