CVE-2026-35544
Roundcube Webmail ≤ 1.5.13
Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:NSummary
CVE-2026-35544 is a medium-severity Incorrect Resource Transfer Between Spheres (CWE-669) vulnerability in Roundcube Webmail. Its CVSS base score is 5.3 (Medium).
Operationally, exploitation aligns with the MITRE ATT&CK technique Escape to Host (T1611); ranked at the 30th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to AC-4 (Information Flow Enforcement) and SC-4 (Information in Shared System Resources) — see the control section below for these in your framework.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-18591
Vulnerability Data
An issue was discovered in Roundcube Webmail before 1.5.14 and 1.6.14. Insufficient Cascading Style Sheets (CSS) sanitization in HTML e-mail messages may lead to a fixed-position mitigation bypass via the use of !important.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
—
—
- 2 hardening rules · 2 OS baselines
—
Mitigating Controls (NIST 800-53 r5) AI
Enforces approved information flow authorizations between system components and connected systems, directly stopping improper resource transfers across spheres.
Prevents unintended information leakage through shared system resources when crossing sphere boundaries.
Monitors and controls communications at external and key internal boundaries to block unauthorized transfers between trust domains.
Enforces logical access authorizations that limit resource transfers to only approved sphere crossings.
Separates user functionality from system management functions to avoid improper resource or behavior transfer between privilege spheres.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Least-privilege authorization policies directly constrain resource transfers across security domains.
Protecting data-in-transit can limit exposure during inter-sphere transfers but does not address control-flow or authorization errors.
Logical segmentation and access controls reduce unintended cross-sphere resource movement.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Environment separation limits unintended resource leakage between spheres.
Information-transfer rules can prevent improper resource hand-off between spheres.
Access-control policies limit unintended control over transferred resources.
Managing access rights reduces risk of unauthorized resource transfer.
Network-security controls can block improper cross-sphere transfers.
Network segregation directly limits unintended resource movement between spheres.