# CVE-2021-26929: Cross-site scripting in n/a

> Attackers can execute arbitrary JavaScript via crafted plain text emails in Horde Groupware Webmail, potentially leading to session hijacking or data theft.

- **Severity:** Medium 6.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 14 Feb 2021
- **Updated:** 3 Aug 2024
- **Also known as:** DEBIAN-CVE-2021-26929, DLA-2564-1, GHSA-qc5g-54hm-vfmc, UBUNTU-CVE-2021-26929

## What is CVE-2021-26929?

CVE-2021-26929 is a medium-severity cross-site scripting vulnerability in Debian Debian Linux, published on 14 Feb 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

An XSS issue was discovered in Horde Groupware Webmail Edition through 5.2.22 (where the Horde_Text_Filter library before 2.3.7 is used). The attacker can send a plain text e-mail message, with JavaScript encoded as a link or email that is mishandled by preProcess in Text2html.php, because bespoke use of \x00\x00\x00 and \x01\x01\x01 interferes with XSS defenses.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2021-26929?

It affects 2 products.


Products: Debian Debian Linux, Horde Groupware.

## How do I fix CVE-2021-26929?

Upgrade to a fixed version.

## Is CVE-2021-26929 being exploited?

There is no known exploitation of CVE-2021-26929 in the wild and no public exploit code.

Public exploit code:

- Horde Groupware Webmail 5.2.22 - Stored XSS (exploitdb)

## 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-2021-26929 and fix it if it is affected.

What it is: CVE-2021-26929 is a medium-severity cross-site scripting vulnerability in Debian Debian Linux, published on 14 Feb 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2021-26929 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-2021-26929/ (Markdown: https://insights.sbomify.com/CVE-2021-26929/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-26929
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-26929
- OSV: https://osv.dev/vulnerability/CVE-2021-26929

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-26929/
Summaries are generated and may contain mistakes; the official description above is the record.