CVE-2026-26079VulnerabilityPublished 11 Feb 2026

CVE-2026-26079: Roundcube Webmail · Untrusted Functionality Inclusion

Affects Roundcube WebmailSource CVE Database V5

Not known to be exploited · CVSS 4.7 Medium : upgrade to 1.6.13 or 1.5.13 when convenient.

Data as of 25 Oct 2026, 19:02 UTC

CVSS 3.1 base score

4.7Medium

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

EPSS: 0.3% chance of exploitation in 30 days – higher than 28% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 1.6.13, 1.5.13

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: Required
Scope: Changed
Confidentiality: Low
Integrity: None
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: Required: Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: None: There is no loss of integrity within 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 11 Feb 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: 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 2026-10-25.

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.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC 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 Roundcube Webmail to 1.6.13 or 1.5.13.

Affected software

Product	Affected	Fixed in
RoundcubeWebmail	Affected <1.5.13 >=1.6.0 <1.6.13	Fixed in 1.6.13 1.5.13

AI-suggested

1. 2. In the interim, implement strict Content Security Policies (CSP) that restrict the execution of inline styles and external CSS from untrusted sources to mitigate CSS injection risks. 3. Sanitize and validate all user inputs and email content that may be rendered in the webmail client, focusing on comment handling and CSS-related inputs. 4. Educate users about the risks of interacting with suspicious emails or links, emphasizing caution with unexpected or unsolicited messages. 5. Monitor webmail logs and network traffic for unusual patterns that may indicate attempts to exploit CSS injection or related attacks. 6. Employ web application firewalls (WAF) with custom rules to detect and block CSS injection payloads targeting Roundcube interfaces. 7. Regularly review and update security configurations and perform penetration testing focused on webmail interfaces to identify residual injection risks. 8. Coordinate with IT and security teams to ensure timely patch management and incident response readiness specific to webmail platforms.

Description

Roundcube Webmail before 1.5.13 and 1.6 before 1.6.13 allows Cascading Style Sheets (CSS) injection, e.g., because comments are mishandled.

Impact

For European organizations, the primary impact of CVE-2026-26079 lies in the potential confidentiality breach. Attackers exploiting this CSS injection vulnerability can manipulate the webmail interface to leak sensitive information, such as email content or session tokens, through CSS-based side-channel attacks. While the vulnerability does not directly compromise integrity or availability, the exposure of confidential information can lead to further attacks, including phishing, account takeover, or lateral movement within networks. Organizations relying on Roundcube Webmail for critical communications may face reputational damage and compliance issues, especially under GDPR regulations that mandate protection of personal data. The requirement for user interaction reduces the likelihood of widespread automated exploitation but targeted spear-phishing campaigns could be effective. The absence of known exploits in the wild currently lowers immediate risk, but the presence of a public CVE and medium severity score means attackers may develop exploits soon. European sectors such as government, finance, and healthcare, which often use open-source solutions like Roundcube, could be particularly sensitive to this threat due to the sensitive nature of their communications.

CWE-829Inclusion of Functionality from Untrusted Control Sphere (opens in a new tab)
Base weaknessOWASP Top 10 A08:2025: Software or Data Integrity Failures (opens in a new tab)
The product imports, requires, or includes executable functionality (such as a library) from a source that is outside of the intended control sphere.
Architecture and Design · Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
Architecture and Design · Enforcement by Conversion
When the set of acceptable objects, such as filenames or URLs, is limited or known, create a mapping from a set of fixed input values (such as numeric IDs) to the actual filenames or URLs, and reject all other inputs.
Architecture and Design
For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks…
OWASP Cheat Sheets
Docker Security (opens in a new tab)
Vulnerable Dependency Management (opens in a new tab)
Software Supply Chain Security (opens in a new tab)
Infrastructure as Code (opens in a new tab)
OWASP ASVS 4.0.3
V12.3.6 (opens in a new tab)
V14.2.3 (opens in a new tab)
V14.2.4 (opens in a new tab)
Attack patterns
Serialized Data External Linking (opens in a new tab)
DTD Injection (opens in a new tab)
Local Code Inclusion (opens in a new tab)
PHP Local File Inclusion (opens in a new tab)
Remote Code Inclusion (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 18 Feb 2026, 09:51 UTC

WeaknessesCWE-829

Technical details

References

Community reviews

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