CVE-2026-107734 in SumatraPDF
Summary
by MITRE • 10/09/2026
SumatraPDF is a multi-format reader for Windows. In 3.5.2 and earlier, an attacker-controlled SyncTeX source filename is substituted for the %f placeholder in an external editor command line without safe Windows argument quoting, and the resulting command line is passed to CreateProcessW(). A user with an external editor configured or auto-detected who opens a PDF with a crafted .synctex.gz file and invokes inverse search can inject command-line flags; the resulting impact depends on the target editor interpreting those flags and can include unintended editor actions or code execution through a malicious extension. No broader impact is claimed beyond the advisory-supported conditions. No fixed version is available as of this review.
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Analysis
by VulDB Data Team • 10/09/2026
The vulnerability identified in SumatraPDF versions 3.5.2 and earlier represents a critical command injection flaw rooted in improper handling of user-supplied input during inverse search operations. This specific issue arises when the application processes SyncTeX source filenames, which are used to map locations within compiled documents back to their original source files for editing purposes. When an external editor is configured or auto-detected by SumatraPDF, the software constructs a command line string that includes placeholders such as %f to represent the filename. The core technical flaw lies in the failure to apply safe Windows argument quoting around these filenames before passing them to the CreateProcessW function. This lack of proper sanitization allows an attacker who controls the content of a .synctex.gz file, which is generated during LaTeX compilation processes, to inject arbitrary command-line flags into the execution string.
The operational impact of this vulnerability is significant for users who rely on SumatraPDF in conjunction with external text editors or integrated development environments that support inverse search functionality. By crafting a malicious SyncTeX source filename containing special characters such as spaces, quotes, or shell metacharacters depending on the underlying system interpretation, an attacker can alter the behavior of the launched editor process. The consequences are not limited to simple display errors; they extend to unintended editor actions and potentially remote code execution if the target application interprets injected flags in a way that triggers malicious extensions or scripts. For instance, if the external editor supports plugins or macros, the injected command line could be interpreted as instructions to load and execute harmful code, thereby compromising the integrity of the user's system under the context of the currently logged-in user account.
This vulnerability aligns with Common Weakness Enumeration category CWE-78 Improper Neutralization of Special Elements used in an OS Command, commonly known as OS Command Injection. The attack vector is classified within MITRE ATT&CK framework techniques related to command and script interpretation, specifically leveraging local application configuration for persistence or execution. Since the vulnerability requires user interaction such as opening a specific PDF file with a crafted SyncTeX source and invoking inverse search, it represents an indirect but potent threat surface in academic and technical writing workflows where LaTeX compilation is common. The absence of a fixed version at the time of review highlights the severity of the oversight in input validation practices within the application's command construction logic.
Mitigation strategies for this vulnerability primarily involve administrative controls and user awareness until a patched release becomes available. Users should avoid using external editors with inverse search capabilities when opening PDFs from untrusted sources, particularly those derived from LaTeX documents where SyncTeX files might be manipulated. Alternatively, disabling the automatic detection of external editors or manually configuring them to use strict quoting mechanisms can reduce risk if such options are exposed in the application settings. Security practitioners should also monitor for updates regarding SumatraPDF and apply patches immediately upon release. Organizations relying on this software for document review should implement network segmentation and application whitelisting policies to limit the potential impact of any successful exploitation, ensuring that even if command injection occurs, the resulting process execution is constrained by strict security boundaries.