Calibre CVE-2026-33205

Real-world risk is moderate-to-high despite absent CVSS scoring and EPSS data in available sources. Attack vector is network-based with no authenticated access required (SSRF vulnerabilities typically have PR:N), and attack complexity appears low given the straightforward endpoint manipulation described. The vulnerability enables blind SSRF, which is automatable and allows enumeration and exfiltration from internal resources. Exploitation does not require user interaction beyond crafting a malicious URL or embedded resource in an e-book file. No public exploit code or active exploitation via CISA KEV confirmation has been identified, reducing immediate pressure. However, the combination of a patched vulnerability in a widely-used e-book application, a clear attack vector through document content, and information disclosure potential warrants prioritized patching. The sandbox-bypass dimension elevates risk beyond typical SSRF scenarios.

An attacker creates a specially crafted e-book file (EPUB, AZW, or similar format) that embeds a malicious background-image URL pointing to an internal service, such as http://169.254.169.254/latest/meta-data (AWS metadata endpoint) or http://localhost:8080/admin/config. When a user opens the e-book in calibre versions prior to 9.6.0, the web view renderer automatically requests the background-image, causing the calibre server to perform the SSRF request. The attacker receives timing responses or error messages that leak information about accessible internal services, or captures response bodies if the endpoint returns data. No direct user interaction (beyond opening a file) or authentication is required, making this exploitable via e-book sharing or distribution channels.