CVE-2026-73248: calibre: Bypass of Python template restrictions via nested `template()` leading to RCE

Severity: high (CVSS 8.5 v4.0)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-08-11 · updated 2026-10-24
Weakness: CWE-94

Description

calibre is an e-book manager. Prior to 9.12.0, calibre processes attacker-controlled composite_template metadata from a malicious EPUB, OPF, PDF, or similar file through program: and a nested template() call whose formatter does not inherit allow_python_templates=False, allowing a nested python: template to reach compile_python_template and execute arbitrary Python code when the file is opened or imported. This issue is fixed in version 9.12.0.

Affected products

kovidgoyal calibre: before 9.12.0

References

https://github.com/kovidgoyal/calibre/commit/dac9990458374a81a5372a768bba6527d965aac8
https://github.com/kovidgoyal/calibre/releases/tag/v9.12.0
https://github.com/kovidgoyal/calibre/security/advisories/GHSA-4f7g-rjfp-hmvx
https://github.com/kovidgoyal/calibre/security/advisories/GHSA-4f7g-rjfp-hmvx

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