How severe is CVE-2026-35540?

CVE-2026-35540 has a CVSS 3.x base score of 5.4, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2026-35540 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (23rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-35540?

CVE-2026-35540 affects Roundcube Webmail. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-35540?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-35540 have an EU (EUVD) identifier?

Yes. CVE-2026-35540 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-18583.

When was CVE-2026-35540 published?

CVE-2026-35540 was published on 2026-04-03 and last updated on 2026-06-17.

CVE-2026-35540

CVE-2026-35540 is a medium-severity vulnerability in Roundcube Webmail with a CVSS 3.x base score of 5.4. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-669.

Key facts

Severity: Medium (CVSS 3.x base score 5.4)
EPSS exploit prediction: 0% (23rd percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-18583
Weakness: CWE-669
Affected product: Roundcube Webmail
Published: 2026-04-03
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2026-35540?: 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.
How severe is CVE-2026-35540?: CVE-2026-35540 has a CVSS 3.x base score of 5.4, rated medium severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2026-35540 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (23rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-35540?: CVE-2026-35540 affects Roundcube Webmail. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-35540?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-35540 have an EU (EUVD) identifier?: Yes. CVE-2026-35540 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-18583.
When was CVE-2026-35540 published?: CVE-2026-35540 was published on 2026-04-03 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:roundcube:webmail:*:*:*:*:*:*:*:*

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