CVE-2026-4827: Insufficient Entropy Auth Bypass Flaw

CVE-2026-4827 Overview

CVE-2026-4827 is an insufficient entropy vulnerability [CWE-331] affecting session-management protections. An attacker on the network can predict or reproduce session identifiers due to weak randomness, leading to unauthorized access. The vulnerability is documented in a Schneider Electric security advisory and requires user interaction for successful exploitation.

The flaw scores 8.7 on the CVSS 4.0 scale. While no public exploit code is available and the issue is not listed on the CISA Known Exploited Vulnerabilities catalog, the network-accessible attack surface and the high confidentiality and integrity impact warrant prompt remediation.

Critical Impact

An unauthenticated attacker on the network can exploit predictable session tokens to hijack sessions and gain unauthorized access to the affected system.

Affected Products

• Schneider Electric product line referenced in advisory SEVD-2026-132-02
• Specific affected models and firmware versions are listed in the vendor security notice
• Refer to the Schneider Electric Security Notice for the authoritative product and version list

Discovery Timeline

• 2026-05-12 - CVE-2026-4827 published to NVD
• 2026-05-14 - Last updated in NVD database

Technical Details for CVE-2026-4827

Vulnerability Analysis

The vulnerability stems from insufficient entropy in the generation of session identifiers used by the affected product. Session-management protections rely on tokens that are unpredictable to external observers. When the underlying random number generator produces values from a limited or guessable range, attackers can enumerate or predict valid session identifiers.

Exploitation requires that the attacker be positioned on the network with reachability to the target service. The CVSS 4.0 vector indicates user interaction is part of the attack chain, suggesting the attacker may need a legitimate user to initiate or hold an active session that can then be predicted or replayed. Successful exploitation compromises confidentiality and integrity of the targeted session, with limited availability impact.

Root Cause

The root cause is categorized as Insufficient Entropy [CWE-331]. Session tokens generated by the affected component do not draw from a cryptographically secure source with adequate bit-strength. This produces identifiers whose value space is small enough, or whose distribution is biased enough, to allow practical guessing or brute-force enumeration within the lifetime of a valid session.

Attack Vector

The attack vector is network-based. An attacker who can communicate with the vulnerable service observes or predicts session token formats, then submits requests bearing forged tokens to assume the identity of authenticated users. Because authentication state is bound to the token alone, a correct guess grants the attacker the privileges associated with that session.

No public proof-of-concept code has been released. The exploitation mechanism is described in prose because no verified code samples are available. Refer to the Schneider Electric Security Notice for vendor-supplied technical details.

Detection Methods for CVE-2026-4827

Indicators of Compromise

• Repeated authentication or session-resume requests from a single source carrying sequentially varying session token values
• Successful access events from network locations that do not match the authenticated user's normal source addresses
• Concurrent active sessions for the same user account originating from disparate IP addresses within a short time window

Detection Strategies

• Inspect application and proxy logs for high-volume requests submitting many distinct session identifiers against the same endpoint
• Correlate session establishment events with subsequent privileged actions to identify sessions that lack a preceding authentication step
• Apply statistical analysis to observed session tokens to detect low-entropy patterns that match the vulnerable generator

Monitoring Recommendations

• Enable verbose authentication and session-lifecycle logging on the affected systems and forward events to a central analytics platform
• Alert on session token reuse across different source addresses or user-agent fingerprints
• Monitor outbound network connections from devices that handle sessions for unexpected administrative actions following session establishment

How to Mitigate CVE-2026-4827

Immediate Actions Required

• Apply the fixes and configuration changes published in Schneider Electric advisory SEVD-2026-132-02 as soon as they are validated in your environment
• Restrict network reachability to the affected service using firewalls, VLAN segmentation, or VPN-only access until the patch is deployed
• Force session invalidation and require re-authentication for all active users following remediation

Patch Information

Schneider Electric has published remediation guidance in advisory SEVD-2026-132-02. Administrators should consult the Schneider Electric Security Notice for affected versions, fixed firmware releases, and step-by-step upgrade procedures.

Workarounds

• Place the affected service behind a reverse proxy or gateway that issues its own high-entropy session tokens and enforces strict session timeouts
• Reduce session lifetimes to the shortest interval acceptable for operations to shrink the window for token prediction
• Require an additional authentication factor on sensitive operations so that a hijacked session alone is insufficient for privileged access