CVE-2025-3091: Authentication Bypass Vulnerability

CVE-2025-3091 Overview

CVE-2025-3091 describes an authorization flaw that allows a low-privileged remote attacker to authenticate as another user. The attacker only needs possession of the victim's second authentication factor. Knowledge of the victim's password is not required. The issue is tracked under CWE-639: Authorization Bypass Through User-Controlled Key and is documented in two CERT@VDE advisories.

Critical Impact
An attacker holding another user's second factor can fully impersonate that user, gaining the victim's privileges and access to confidentiality, integrity, and availability of their data.

Affected Products

Products covered by CERT@VDE Advisory VDE-2025-035
Products covered by CERT@VDE Advisory VDE-2025-038
Specific vendor and product identifiers were not enumerated in the NVD record

Discovery Timeline

2025-06-24 - CVE-2025-3091 published to NVD
2026-04-15 - Last updated in NVD database

Technical Details for CVE-2025-3091

Vulnerability Analysis

The vulnerability lies in the authentication workflow's handling of multi-factor authentication (MFA). The affected system treats possession of a valid second factor as sufficient evidence of identity. It does not enforce a successful first-factor (password) verification bound to the same user session.

An authenticated low-privileged attacker who has obtained another user's second factor can authenticate to the application as that user. The attacker inherits the victim's roles and privileges. This is an authorization bypass through user-controlled key, classified as [CWE-639].

The published CVSS vector indicates network reachability and high attack complexity, reflecting the precondition that the attacker must already hold the victim's second factor. Once that condition is met, the impact on confidentiality, integrity, and availability of the victim's account is high.

Root Cause

The root cause is a broken access control design in the login flow. The MFA verification step does not require that the second factor be cryptographically or logically bound to the same identity that completed the first factor. The user identifier used to look up the account during second-factor validation can be substituted, allowing one user's second factor to authorize a session for another account.

Attack Vector

An attacker with low-privileged remote access initiates a login as the victim user. During the MFA step, the attacker submits the victim's second factor, which they possess through theft, social engineering, or insider access. The server validates the second factor against the submitted identifier and issues a session bound to the victim. No knowledge of the victim's password is required.

No public proof-of-concept code is available for CVE-2025-3091. Refer to the CERT@VDE Advisory VDE-2025-035 and CERT@VDE Advisory VDE-2025-038 for vendor-specific technical detail.

Detection Methods for CVE-2025-3091

Indicators of Compromise

Authentication events where the user identifier presented at the first-factor step differs from the account ultimately granted the session
Successful logins for a user from a source device or IP not previously associated with that account
Repeated MFA submissions from a single low-privileged session targeting multiple distinct user identifiers
Privilege actions performed by an account immediately after an atypical authentication path

Detection Strategies

Correlate first-factor and second-factor validation log entries and alert when the resolved user identity changes between steps
Baseline normal MFA usage per account and flag MFA token submissions originating from accounts other than the owner
Monitor identity provider telemetry for sessions where MFA succeeded but no corresponding password validation event is present

Monitoring Recommendations

Forward authentication, MFA, and session-issuance logs to a centralized analytics platform with cross-event correlation
Enable alerting on lateral access patterns where a low-privileged user gains a session matching a higher-privileged account
Review CERT@VDE advisories VDE-2025-035 and VDE-2025-038 for vendor-specific log signatures and update detection content accordingly

How to Mitigate CVE-2025-3091

Immediate Actions Required

Apply the vendor patches referenced in CERT@VDE Advisory VDE-2025-035 and CERT@VDE Advisory VDE-2025-038
Rotate or re-enroll second-factor credentials for all users on the affected systems
Review authentication logs for suspicious cross-account MFA usage since deployment
Restrict administrative interfaces to trusted networks until patches are deployed

Patch Information

Consult the CERT@VDE advisories for fixed versions and patch availability. The NVD record does not enumerate specific affected versions, so administrators must map their deployed components to the advisory identifiers VDE-2025-035 and VDE-2025-038 to determine remediation packages.

Workarounds

Limit network exposure of the authentication endpoint to known administrative networks
Require an additional out-of-band approval step for privileged accounts until patches are applied
Enforce strict physical and procedural controls over the distribution and storage of second-factor devices
Disable shared or pooled second-factor devices and ensure each token is bound to a single identity

bash

# Example: restrict authentication endpoint exposure with iptables
iptables -A INPUT -p tcp --dport 443 -s 10.10.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP