VulnerabilityPublished 3 Apr 2026

CVE-2026-35544: Roundcube Webmail · Incorrect Resource Transfer Between Spheres

Affects Roundcube WebmailSource CVE Database V5

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Not known to be exploited · CVSS 5.3 Medium : upgrade to 1.6.14 or 1.5.14 when convenient.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 3.1 base score

5.3Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.3% chance of exploitation in 30 days – higher than 30% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 1.6.14, 1.5.14

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: Low
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 3 Apr 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade Webmail and roundcube/roundcubemail to 1.6.14 or 1.5.14.

Affected software

Product	Affected	Fixed in
RoundcubeWebmail	Affected >=1.6.0 <1.6.14	Fixed in 1.6.14
RoundcubeWebmail	Affected <1.5.14	Fixed in 1.5.14
GitHubroundcube/roundcubemail`pkg:github/roundcube/roundcubemail`Other threats	Affected <1.5.14 <1.6.14	Fixed in 1.5.14 1.6.14

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

If you cannot patch yet, users should exercise caution when opening HTML emails from untrusted sources.

Description

CVE-2026-35544 is a medium severity vulnerability in Roundcube Webmail versions before 1.5.14 and 1.6.14. It involves insufficient sanitization of CSS in HTML email messages, allowing a bypass of fixed-position mitigations through the use of the ! important CSS directive. This vulnerability does not impact confidentiality or availability but can lead to integrity issues.

Impact

The vulnerability allows an attacker to bypass fixed-position CSS mitigations in HTML emails, potentially enabling manipulation of the email display or interface integrity. There is no impact on confidentiality or availability. No known exploits exist in the wild at this time.

Summary

This vulnerability in Roundcube Webmail arises from inadequate sanitization of Cascading Style Sheets (CSS) within HTML email content. Specifically, the sanitization fails to properly handle the !important CSS directive, which can be used to bypass fixed-position mitigation controls. The issue affects versions prior to 1.5.14 and 1.6.14. The CVSS 3.1 base score is 5.3, reflecting a network attack vector with low complexity, no privileges required, no user interaction, and an impact limited to integrity.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 10 Apr 2026, 09:15 UTC

WeaknessesCWE-669

Technical details

References

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