VulnerabilityPublished 9 Feb 2026

CVE-2026-25916: Roundcube Webmail · Unprotected Alternate Channel

Affects Roundcube WebmailSource CVE Database V5

Not known to be exploited · CVSS 4.3 Medium : upgrade to 1.6.13 or 1.5.13 when convenient.

Data as of 26 Oct 2026, 10:12 UTC

CVSS 3.1 base score

4.3Medium

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

EPSS: 0.7% chance of exploitation in 30 days – higher than 54% 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:U/C:L/I:N/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: Required
Scope: Unchanged
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: 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: 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 9 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 26 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.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, 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 Roundcube Webmail to 1.6.13 or 1.5.13.

Affected software

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

AI-suggested

To mitigate CVE-2026-25916, organizations should upgrade Roundcube Webmail installations to version 1.5.13 or 1.6.13 and later, where the SVG feImage blocking issue is resolved. If you cannot patch yet, administrators can implement additional email filtering rules to strip or sanitize SVG content from incoming emails, especially those containing feImage elements. Disabling SVG rendering in the email client or restricting SVG content types can reduce exposure. Network-level controls such as blocking outbound HTTP/HTTPS requests from the webmail server to untrusted domains may limit remote image retrieval. User awareness training to avoid opening suspicious emails can also reduce risk. Monitoring webmail logs for unusual external resource requests may help detect exploitation attempts. Finally, organizations should review their privacy policies and inform users about potential risks related to remote content loading in emails.

Description

CVE-2026-25916 is a medium severity vulnerability in Roundcube Webmail versions before 1.5.13 and 1.6 before 1.6.13. When the 'Block remote images' feature is enabled, the application fails to block SVG feImage elements, allowing remote image content to be loaded. This unprotected alternate channel can be exploited to bypass privacy protections intended to prevent remote content loading, potentially leaking user information. The vulnerability does not impact integrity or availability and requires user interaction to trigger. No known exploits are currently reported in the wild.

Impact

For European organizations, the primary impact of CVE-2026-25916 is the potential leakage of user privacy and metadata through unintended remote image loading in webmail clients. This could lead to unauthorized tracking of email open events and user behavior, undermining confidentiality. Organizations subject to GDPR and other stringent data protection regulations may face compliance risks if user data is inadvertently exposed. While the vulnerability does not compromise system integrity or availability, the privacy implications could erode user trust and expose organizations to regulatory scrutiny. Since Roundcube is widely used in European small to medium enterprises and hosting providers for webmail services, the scope of affected systems is significant. The lack of known active exploits reduces immediate risk, but the ease of exploitation through crafted emails means attackers could leverage this vector for targeted surveillance or phishing campaigns.

CWE-420Unprotected Alternate Channel (opens in a new tab)
Base weakness
The product protects a primary channel, but it does not use the same level of protection for an alternate channel.
Architecture and Design
Identify all alternate channels and use the same protection mechanisms that are used for the primary channels.
OWASP Cheat Sheets
Docker Security (opens in a new tab)
OWASP ASVS 4.0.3
V1.14.1 (opens in a new tab)
V1.4.4 (opens in a new tab)
V1.4.5 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 16 Feb 2026, 13:33 UTC

WeaknessesCWE-420

Technical details

References

Community reviews

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