Calibre EUVD-2026-16612

Local attacker requires user interaction: victim must open a crafted Markdown or text-based e-book file in Calibre prior to version 9.6.0. The ebook reader web view background-image endpoint lacks authentication, enabling unauthenticated file exfiltration.

Although CVSS and EPSS scores are not provided in the available data, this vulnerability presents substantial real-world risk based on multiple factors: the attack vector is network-based requiring only file upload or conversion of a text file (low complexity), no authentication is explicitly required for the background-image endpoint (critical gap), and the technical impact is complete confidentiality breach (arbitrary file read). The presence of two separate vulnerability primitives (path traversal plus SSRF plus missing authentication) chained together increases the attack surface significantly. The attack is highly automatable-an attacker can programmatically generate malicious markdown files and retrieve sensitive files (configuration files, private keys, source code, credentials) without user interaction beyond triggering a conversion. Given that Calibre is a cross-platform desktop and server application used in corporate, educational, and personal environments, affected instances may expose high-value data. KEV status and active exploitation data are not provided, but the straightforward nature of the attack (no complex exploitation required) and the public nature of the GitHub advisory (GitHub_M reporter) suggest moderate to high likelihood of near-term exploitation attempts. This is not merely a high-CVSS academic issue-it is a practical file disclosure vulnerability with clear, direct impact.

An attacker crafts a malicious markdown file containing image references with path traversal sequences (e.g., '') and distributes it to a Calibre user via email or a shared document repository. When the user opens and converts the file in Calibre (a common and expected action), the path traversal flaw allows the conversion process to read the sensitive file from the system. The attacker then accesses the Calibre ebook reader web view and requests the background-image endpoint with a URL pointing to the converted file location, which is returned without authentication checks. The attacker retrieves confidential data such as system configuration files, SSH keys, database credentials, or source code in a single automated attack flow without any special privileges or user interaction beyond the initial file conversion.