CVE-2026-41838: Spring Framework WebSocket Session ID Predictability – Spring Security Risk

Technical summary

CVE-2026-41838 stems from insufficient entropy in WebSocket session ID generation within Spring Framework's spring-websocket module. The vulnerability resides in session identifier creation logic that fails to employ cryptographically secure random number generation. An authenticated attacker could leverage the predictable nature of session IDs in conjunction with inadequate authorization checks to access WebSocket sessions belonging to other authenticated users, potentially exfiltrating session-specific data or hijacking active connections.

Business impact

Organizations relying on Spring Framework for real-time communication features face confidentiality risk. If WebSocket sessions carry sensitive data—such as trading information, user communications, or personal details—session hijacking could lead to unauthorized information disclosure. The requirement for valid credentials limits blast radius, but impacts to multi-tenant or high-privilege accounts could have significant business consequences. Companies with inadequate authorization rules may face compliance violations if sensitive user data becomes accessible.

Affected systems

VMware Spring Framework versions 5.3.0 through 5.3.48, 6.1.0 through 6.1.27, 6.2.0 through 6.2.18, and 7.0.0 through 7.0.7 are vulnerable. Organizations should audit their deployed Spring Framework versions in applications that use WebSocket functionality. Older unsupported versions (pre-5.3.0) should be assessed for end-of-life status.

Exploitability

Exploitation requires an attacker to be an authenticated user (PR:L), accept user interaction to trigger session establishment (UI:R), and have network access to the application (AV:N). The attack complexity is high (AC:H), suggesting that successful exploitation also depends on specific application-level authorization weaknesses. While not trivial, this is not a zero-day scenario—attackers with valid credentials who understand your authorization architecture could craft attacks. Public exploit code availability is not documented.

Remediation

Upgrade Spring Framework to patched versions: apply the latest 7.0.x, 6.2.x, 6.1.x, or 5.3.x release available from VMware. Verify against vendor security advisories for the exact patch versions addressing this CVE. Additionally, review and strengthen authorization rules governing WebSocket session access; ensure that authenticated users cannot access sessions outside their intended scope. Consider implementing per-session capability tokens or explicit ownership validation.

Patch guidance

Check VMware's official Spring Framework security advisory and release notes for the specific patched versions. Apply updates through your standard change management process. Test WebSocket functionality in a staging environment before production rollout. For applications on unsupported versions, plan an upgrade path urgently. Version pinning and dependency scanning in CI/CD pipelines should flag any future regressions in session ID generation.

Detection guidance

Monitor WebSocket logs for authentication failures or unusual session access patterns, particularly successive attempts to connect with different session IDs from the same user account. Review authorization logs to identify unauthorized WebSocket session access. Implement logging of session ID generation and validation; inspect for low entropy in session ID distribution (patterns or sequential values). Network-based detection is difficult without protocol inspection; focus on application-level logging and behavioral anomalies.

Why prioritize this

Although assigned a MEDIUM severity (CVSS 4.8) with high confidentiality impact but limited attack surface due to authentication requirements, this vulnerability should be prioritized for patching because: (1) it directly undermines session security in real-time communication channels, (2) many organizations have weak authorization rules, (3) Spring Framework is ubiquitous in enterprise Java environments, and (4) the fix is straightforward and low-risk. Organizations with multi-tenant SaaS or sensitive WebSocket data should treat this as HIGH priority regardless of CVSS score.

Risk score, explained

CVSS 4.8 reflects a network-exploitable (AV:N) vulnerability requiring authentication (PR:L) and user interaction (UI:R), resulting in high confidentiality impact (C:H) but no integrity or availability loss. The high attack complexity (AC:H) and authentication requirement lower the base score. However, the CVSS does not weight the prevalence of inadequate authorization rules in real-world deployments or the sensitive nature of WebSocket data, making actual risk potentially higher in specific contexts.

Frequently asked questions