# CVE-2021-25633: Content Manipulation with Double Certificate Attack

> Attackers can manipulate ODF document signatures to display valid indicators for altered content, bypassing integrity checks in LibreOffice.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 11 Oct 2021
- **Updated:** 16 Sep 2024
- **Also known as:** DEBIAN-CVE-2021-25633, GHSA-fx8r-3hmx-c78j, UBUNTU-CVE-2021-25633

## What is CVE-2021-25633?

CVE-2021-25633 is a high-severity vulnerability in Debian Debian Linux, published on 11 Oct 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

LibreOffice supports digital signatures of ODF documents and macros within documents, presenting visual aids that no alteration of the document occurred since the last signing and that the signature is valid. An Improper Certificate Validation vulnerability in LibreOffice allowed an attacker to create a digitally signed ODF document, by manipulating the documentsignatures.xml or macrosignatures.xml stream within the document to combine multiple certificate data, which when opened caused LibreOffice to display a validly signed indicator but whose content was unrelated to the signature shown. This issue affects: The Document Foundation LibreOffice 7-0 versions prior to 7.0.6; 7-1 versions prior to 7.1.2.

Weakness: CWE-295 (Improper Certificate Validation)

## Which versions are affected by CVE-2021-25633?

It affects 2 products.


Products: Debian Debian Linux, Libreoffice Libreoffice.

## How do I fix CVE-2021-25633?

Upgrade to a fixed version.

## Is CVE-2021-25633 being exploited?

There is no known exploitation of CVE-2021-25633 in the wild and no public exploit code.

## Other vulnerabilities in Debian Debian Linux

- [CVE-2015-3306](https://insights.sbomify.com/CVE-2015-3306/): ProFTPD Improper Access Control (critical 10.0, exploited in the wild)
- [CVE-2025-49113](https://insights.sbomify.com/CVE-2025-49113/): RoundCube Webmail Deserialization of Untrusted Data (critical 9.9, exploited in the wild)
- [CVE-2026-24061](https://insights.sbomify.com/CVE-2026-24061/): GNU InetUtils Argument Injection (critical 9.8, exploited in the wild)
- [CVE-2025-39682](https://insights.sbomify.com/CVE-2025-39682/): Linux Kernel Improper Check for Unusual or Exceptional Conditions (critical 9.8, exploited in the wild)
- [CVE-2024-9680](https://insights.sbomify.com/CVE-2024-9680/): Mozilla Firefox Use-After-Free (critical 9.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-25633 and fix it if it is affected.

What it is: CVE-2021-25633 is a high-severity vulnerability in Debian Debian Linux, published on 11 Oct 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-25633 in the wild and no public exploit code.

Affected product: Debian Debian Linux. 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-2021-25633/ (Markdown: https://insights.sbomify.com/CVE-2021-25633/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-25633
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-25633
- OSV: https://osv.dev/vulnerability/CVE-2021-25633

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-25633/
Summaries are generated and may contain mistakes; the official description above is the record.