# CVE-2026-35544: Roundcube Webmail: Insufficient CSS sanitization in HTML e-mail messages

> Attackers can bypass CSS sanitization in Roundcube Webmail using !important rules, potentially enabling UI redressing or content spoofing attacks.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/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:** 3 Apr 2026
- **Updated:** 3 Apr 2026
- **Also known as:** DEBIAN-CVE-2026-35544, GHSA-xpqh-grpw-4xmg, UBUNTU-CVE-2026-35544

## What is CVE-2026-35544?

CVE-2026-35544 is a medium-severity vulnerability in Roundcube Webmail, published on 3 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

An issue was discovered in Roundcube Webmail before 1.5.14 and 1.6.14. Insufficient Cascading Style Sheets (CSS) sanitization in HTML e-mail messages may lead to a fixed-position mitigation bypass via the use of !important.

Weakness: CWE-669 (Incorrect Resource Transfer Between Spheres)

## Which versions are affected by CVE-2026-35544?

2 open source packages ship an affected version, including roundcube/roundcubemail. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `roundcube/roundcubemail` | Packagist | From 1.7-beta | 1.7-rc5 |
| `roundcube/roundcubemail` | Packagist | From 1.7-beta | 1.7-rc5 |

Products: Roundcube Webmail.

## How do I fix CVE-2026-35544?

Upgrade roundcube/roundcubemail to 1.7-rc5 or later.

## Is CVE-2026-35544 being exploited?

There is no known exploitation of CVE-2026-35544 in the wild and no public exploit code.

## Other vulnerabilities in Roundcube Webmail

- [CVE-2024-42009](https://insights.sbomify.com/CVE-2024-42009/): RoundCube Webmail Cross-Site Scripting (critical 9.3, exploited in the wild)
- [CVE-2025-68461](https://insights.sbomify.com/CVE-2025-68461/): RoundCube Webmail Cross-site Scripting (high 7.2, exploited in the wild)
- [CVE-2008-5619](https://insights.sbomify.com/CVE-2008-5619/): PHPMailer susceptible to arbitrary code execution (critical 10.0)
- [CVE-2024-37385](https://insights.sbomify.com/CVE-2024-37385/): Command injection in n/a (critical 9.8)
- [CVE-2024-42008](https://insights.sbomify.com/CVE-2024-42008/): Cross-site scripting in n/a (critical 9.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-35544 and fix it if it is affected.

What it is: CVE-2026-35544 is a medium-severity vulnerability in Roundcube Webmail, published on 3 Apr 2026. 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-2026-35544 in the wild and no public exploit code.

Affected packages and fixed versions:
- roundcube/roundcubemail (Packagist): affected from 1.7-beta; fixed in 1.7-rc5
- roundcube/roundcubemail (Packagist): affected from 1.7-beta; fixed in 1.7-rc5

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-2026-35544/ (Markdown: https://insights.sbomify.com/CVE-2026-35544/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-35544
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-35544
- OSV: https://osv.dev/vulnerability/CVE-2026-35544

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-35544/
Summaries are generated and may contain mistakes; the official description above is the record.