# CVE-2026-27810: calibre Vulnerable to HTTP Response Header Injection

> Authenticated users can inject arbitrary HTTP headers into calibre Content Server responses via unsanitized query parameters, potentially bypassing security controls.

- **Severity:** Medium 6.4 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 27 Feb 2026
- **Updated:** 2 Mar 2026
- **Also known as:** DEBIAN-CVE-2026-27810, GHSA-5fpj-fxw7-8grw, UBUNTU-CVE-2026-27810

## What is CVE-2026-27810?

CVE-2026-27810 is a medium-severity vulnerability in kovidgoyal calibre, published on 27 Feb 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

calibre is a cross-platform e-book manager for viewing, converting, editing, and cataloging e-books. Prior to version 9.4.0, an HTTP Response Header Injection vulnerability in the calibre Content Server allows any authenticated user to inject arbitrary HTTP headers into server responses via an unsanitized `content_disposition` query parameter in the `/get/` and `/data-files/get/` endpoints. All users running the calibre Content Server with authentication enabled are affected. The vulnerability is exploitable by any authenticated user and can also be triggered by tricking an authenticated victim into clicking a crafted link. Version 9.4.0 contains a fix for the issue.

Weakness: CWE-113 (Improper Neutralization of CRLF Sequences in HTTP Headers)

## Which versions are affected by CVE-2026-27810?

It affects 1 product.


Products: Calibre-Ebook Calibre.

## How do I fix CVE-2026-27810?

Upgrade to a fixed version.

## Is CVE-2026-27810 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-27810 exists.

## Other vulnerabilities in kovidgoyal calibre

- [CVE-2011-4124](https://insights.sbomify.com/CVE-2011-4124/): Command injection in Calibre (critical 9.8)
- [CVE-2011-4125](https://insights.sbomify.com/CVE-2011-4125/): Privilege escalation in Calibre (critical 9.8)
- [CVE-2026-26064](https://insights.sbomify.com/CVE-2026-26064/): calibre: Path Traversal Vulnerability Enables Arbitrary File Write and Remote Code Execution (critical 9.3)
- [CVE-2026-26065](https://insights.sbomify.com/CVE-2026-26065/): calibre: Path Traversal can Lead to Arbitrary File Write and Potential Code Execution (critical 9.3)
- [CVE-2026-25635](https://insights.sbomify.com/CVE-2026-25635/): calibre has a Path Traversal Leading to Arbitrary File Write and Potential Code Execution (high 8.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-27810 and fix it if it is affected.

What it is: CVE-2026-27810 is a medium-severity vulnerability in kovidgoyal calibre, published on 27 Feb 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-27810 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-2026-27810/ (Markdown: https://insights.sbomify.com/CVE-2026-27810/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-27810
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-27810
- OSV: https://osv.dev/vulnerability/CVE-2026-27810

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-27810/
Summaries are generated and may contain mistakes; the official description above is the record.