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MEDIUM severity

CVE-2026-35540 — roundcubemail

MEDIUMFix: roundcube/roundcubemail@27ec6cc

CVE-2026-35540 is a medium-severity (CVSS 5.4) CWE-669 vulnerability in roundcube/roundcubemail. A fix is available for roundcube/roundcubemail — see the affected versions and patch details below.

Roundcube Webmail: Insufficient CSS sanitization in HTML e-mail messages

Also known asGHSA-vxg2-hhgr-37fx
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Nov 3, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-35540.

EPSS Exploitation Probability

via FIRST.org ↗
0.4%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs34th percentile — riskier than 34% of all scored CVEsHighest risk
0.00%0.31%0.62%0.93%0.0%0.4%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected
🐘roundcube/roundcubemail

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.

Description

An issue was discovered in Roundcube Webmail 1.6.0 before 1.6.14. Insufficient Cascading Style Sheets (CSS) sanitization in HTML e-mail messages may lead to SSRF or Information Disclosure, e.g., if stylesheet links point to local network hosts.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐘Packagistroundcube/roundcubemail≥ 1.7-beta&&< 1.7-rc51.7-rc5composer require roundcube/roundcubemail:^1.7-rc5

Affected Products

1 product · 1 configurations
Application
webmailroundcube
≥ 1.6.0 && < 1.6.14
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for roundcube/roundcubemail, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update roundcube/roundcubemail to 1.7-rc5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-35540 is resolved across your whole dependency graph.

  3. Workarounds

    Restrict outbound requests from the affected component to an allowlist of hosts, block access to link-local and internal address ranges at the network layer, and require authentication on internal services so a forged request cannot reach them unauthenticated.

Frequently Asked Questions

An issue was discovered in Roundcube Webmail 1.6.0 before 1.6.14. Insufficient Cascading Style Sheets (CSS) sanitization in HTML e-mail messages may lead to SSRF or Information Disclosure, e.g., if stylesheet links point to local network hosts.
O3 Security · Impact-Aware SCA

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CVE-2026-35540: roundcubemail SSRF — Fixed in 1.7-rc5