External risk intelligence

Roundcube Webmail SVG Remote Image Block Bypass Leads to Information Disclosure or Privilege Escalation

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2026-75003

Roundcube is a webmail application designed to be a public-facing service accessible over the internet for users to access their email, making its interface and processing components inherently exposed to network traffic.

Privilege Escalation

Roundcube Webmail

1.6.0 to before 1.6.181.7.0 to before 1.7.3

Halo Surface Signal: 5 out of 5 — more likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

This vulnerability impacts Roundcube webmail, a widely used email client, and could allow attackers to potentially access sensitive information or gain unauthorized control by bypassing security measures through specially crafted SVG images. The primary concern is confirming if your organization utilizes this specific webmail service.

Unclosed code in SVG images bypasses security.
Affects webmail, enabling sensitive data access.
Verify if your organization uses this service.

Attack Path

How an attacker could exploit the issue

An attacker could exploit this vulnerability by sending a specially crafted SVG image to a Roundcube Webmail instance. This image, containing an unclosed `url()` within a `FuncIRI` attribute, could bypass the remote image blocking mechanism. If successful, this could allow the attacker to access sensitive information or potentially gain elevated privileges within the webmail system.

No authentication required for access.
Malicious SVG image uploaded or embedded.
Information disclosure or privilege escalation.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could allow an attacker to bypass remote image blocking, potentially leading to the disclosure of sensitive information or the escalation of privileges within the Roundcube Webmail application under certain conditions.

User emails and account data.
Malicious SVG via remote image loading.
Unauthorized access or data compromise.

Operational Fix

Recommended remediation, mitigation, and detection steps

The Roundcube Webmail platform's security flaw, allowing potential information disclosure or privilege escalation, likely falls under the responsibility of platform or infrastructure teams managing the webmail service. The first practical step is to pinpoint all instances of the affected Roundcube version, assess their internet reachability and business criticality, and identify the specific system owners. This will inform a prioritized remediation plan, potentially involving coordinated updates or vendor engagement.

Platform or application owners should take charge.
Verify internet-facing instances first.
Plan updates during maintenance windows.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is Roundcube Webmail?

Roundcube Webmail is a browser-based email client written in PHP. It provides a familiar interface for managing electronic mail, including features like folders, address books, and message composition. Because it sits between a user's browser and the mail server, it acts as a gateway for processing incoming and outgoing data, including attachments and embedded content like images.

How does CVE-2026-75003 exploit SVG images?

This vulnerability involves a weakness classified as CWE-669 (Importing Untrusted Data). In Roundcube, the software is designed to block remote images for privacy. However, a malformed 'url()' tag within an SVG file's attribute can confuse the system's filtering logic. This allows the image to load despite the security controls, which could then be used to leak sensitive data or elevate an attacker's access rights.

Does viewing any email trigger this vulnerability?

No. The issue is specific to how the application processes embedded SVG images that contain this malformed syntax. If an email does not contain an SVG file, or if the SVG file does not include the specific unclosed 'url()' pattern in its attributes, the bypass mechanism is not triggered.

Why should I care if my Roundcube instance is internet-facing?

According to Halo Surface Signal, Roundcube is inherently designed to be a public-facing service. Because it is accessible over the internet to allow remote email access, any vulnerability that bypasses security controls makes the service a primary target for remote attackers. Internet-facing instances are therefore at a much higher risk of exploitation than internal, isolated services.

How do I respond to this threat?

The most effective first step is to perform an inventory of all Roundcube Webmail installations within your environment. Once you have identified which versions are running, prioritize updating any instances on versions 1.6.x before 1.6.18 or 1.7.x before 1.7.3. Coordinate with your platform or infrastructure team to schedule these updates during a maintenance window to minimize service disruption.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.