CVE-2025-49113 is a deserialization of untrusted data vulnerability in Roundcube Webmail. CISA added it to the Known Exploited Vulnerabilities catalogue on 20 February 2026, which means attackers have used it in real attacks. Organisations running the affected product should apply the vendor fix or mitigation as a priority.
What This Vulnerability Means in Roundcube Webmail
deserialization of untrusted data is dangerous because an application may reconstruct attacker-controlled input into executable objects or state. In a webmail product, that can turn a single crafted request into code execution, authentication bypass, or unauthorized access to mail data and account context.
For Roundcube, the practical significance is not abstract, it is that the vulnerable mail application itself can become the entry point. Once deserialization is reached, the attacker is no longer constrained to normal user workflows, so the security boundary between web input and server-side execution matters more than the usual mailbox feature set.
How Organisations Check Exposure and Prioritise Response
Exposure starts with asset inventory: identify every internet-facing or internally reachable Roundcube deployment, then confirm whether it matches the affected product line described in the vendor advisory. Public exposure raises urgency because unauthenticated or weakly protected webmail endpoints are easier to probe and exploit at scale.
CISA placing this CVE in the Known Exploited Vulnerabilities catalogue means it should be treated as active-exploitation priority, not routine backlog. The most reliable sources for version and fix detail are the CVE Program record and the vendor advisory, with environment-specific confirmation coming from your own asset and internet-exposure review.
Remediation, Compensating Controls and Verification
The preferred response is to apply the vendor fix or mitigation as soon as possible, then reduce exposure while change windows or compatibility checks are pending. If immediate patching is blocked, place the service behind stronger access controls, restrict who can reach the webmail interface, and minimise the attack surface around the application host.
Because vulnerable web applications are often patched after attackers have already tested them, remediation should be followed by validation rather than assumption. The Vulnerability Management Guide is useful here because it reflects the practical workflow of scope, prioritisation, remediation and verification that this kind of KEV-listed issue demands.
Detection, Compromise Review and Identity Impact
After patching, review whether the system was already touched before the fix landed. Look for unusual web requests, unexpected application behaviour, new files or configuration changes, and signs that the server or adjacent mail accounts were used in ways that do not fit normal mailbox operations.
If exploitation is suspected, treat mail access as potentially exposed. Reset credentials, invalidate active sessions where the product or environment supports it, and review any service or integration accounts that the webmail platform relies on. The broader lesson is consistent with the State of NHI & AI Agent Breach Report 2026: when attackers get execution or token-level access through a vulnerable service, the downstream problem is often credential and session abuse, not just the original CVE.
Risk and Threat Considerations
This vulnerability is high-risk because it sits in a remotely reachable collaboration service that often holds authenticated sessions, stored mail content and trust relationships with internal users. If exploited, it can become a bridge from a web request to broader mailbox compromise, persistence or lateral movement through email-based trust.
Failure mechanism: attacker-controlled input reaches a deserialization routine, the application reconstructs unsafe objects or state, and that can trigger arbitrary server-side behaviour before the defender notices.
Impact: the attacker may gain unauthorized access to webmail data, execute code in the application context, steal credentials or sessions, and use the mail platform as a foothold for further compromise.
Standards & Framework Alignment
This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.
CIS Controls v8, NIST SP 800-53 Rev 5 and OWASP ASVS set the governance and control requirements practitioners need to meet.
| Framework | Control / Reference | Relevance |
|---|---|---|
| CIS Controls v8 | CIS-1 — Inventory and Control of Enterprise Assets | Roundcube exposure depends on knowing where the webmail service is deployed. |
| CIS-7 — Continuous Vulnerability Management | This KEV-listed CVE requires prioritised vulnerability handling and verification. | |
| Recommendation — Inventory every Roundcube instance and map internet-facing exposure before triaging remediation. Prioritise the vulnerable Roundcube service for remediation and validate that the fix is effective. | ||
| NIST SP 800-53 Rev 5 | SI-2 — Flaw Remediation | The subject is a software flaw requiring prompt correction and tracking. |
| SC-7 — Boundary Protection | Internet exposure of a webmail service materially affects exploitability and containment. | |
| Recommendation — Apply flaw remediation controls to remove the vulnerable Roundcube condition and confirm closure. Restrict access paths to the webmail service and reduce direct exposure where possible. | ||
| OWASP ASVS | V5 — File Handling | Deserialization weaknesses often arise in unsafe handling of serialized application data. |
| Recommendation — Review server-side handling of persisted and inbound data paths for unsafe object reconstruction. | ||
Related resources from NHI Mgmt Group
- CVE-2025-26399 (SolarWinds Web Help Desk Deserialization of Untrusted Data)
- CVE-2026-20131 (Cisco Secure Firewall Management Center (FMC) Software and Cisco Security Cloud Control (SCC) Firewall Management Deserialization of Untrusted Data)
- CVE-2021-23758 (Ajax.NET Professional Deserialization of Untrusted Data)
- CVE-2023-21529 (Microsoft Exchange Server Deserialization of Untrusted Data)