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

> An attacker can execute arbitrary Python code by tricking a user into opening a malicious e-book file with crafted metadata.

- **Severity:** High 8.5 (`CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 11 Aug 2026
- **Updated:** 12 Aug 2026
- **Also known as:** DEBIAN-CVE-2026-73248, GHSA-4f7g-rjfp-hmvx, UBUNTU-CVE-2026-73248

## What is CVE-2026-73248?

CVE-2026-73248 is a high-severity code injection vulnerability in kovidgoyal calibre, published on 11 Aug 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official 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.

Weakness: CWE-95 (Improper Neutralization of Directives in Dynamically Evaluated Code), CWE-94 (Improper Control of Generation of Code)

## Which versions are affected by CVE-2026-73248?


## How do I fix CVE-2026-73248?

Upgrade to a fixed version.

## Is CVE-2026-73248 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-73248 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-73248 and fix it if it is affected.

What it is: CVE-2026-73248 is a high-severity code injection vulnerability in kovidgoyal calibre, published on 11 Aug 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-73248 exists.

Affected product: kovidgoyal calibre. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-73248/ (Markdown: https://insights.sbomify.com/CVE-2026-73248/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-73248
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-73248
- OSV: https://osv.dev/vulnerability/CVE-2026-73248

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-73248/
Summaries are generated and may contain mistakes; the official description above is the record.