CVE-2026-43827: Apache Shiro Auth Bypass Vulnerability

CVE-2026-43827 Overview

CVE-2026-43827 is a session fixation vulnerability [CWE-384] affecting default configurations of Apache Shiro, a widely used Java security framework. The flaw exists because Shiro does not invalidate an existing session upon successful authentication, nor does it generate a new session identifier. An attacker who can pre-set or obtain a victim's session identifier before login can reuse that same identifier post-authentication. This allows the attacker to ride the authenticated session and impersonate the victim.

The issue affects Apache Shiro versions 1.0 through 2.1.0, and 3.0.0-alpha-1. The Apache Shiro project has released fixed versions 2.1.1 and 3.0.0-alpha-2.

Critical Impact

Successful exploitation enables an attacker to hijack an authenticated user session, gaining the privileges of the victim within applications that rely on Apache Shiro's default session management.

Affected Products

• Apache Shiro versions 1.0 through 2.1.0
• Apache Shiro 3.0.0-alpha-1
• Applications and frameworks embedding the affected Shiro releases with default session configuration

Discovery Timeline

• 2026-05-25 - CVE-2026-43827 published to NVD
• 2026-05-25 - Issue disclosed via the Openwall OSS-Security mailing list
• 2026-05-28 - Last updated in NVD database

Technical Details for CVE-2026-43827

Vulnerability Analysis

Apache Shiro manages user sessions through its SessionManager and Subject APIs. In the affected versions, the framework's default behavior preserves the pre-authentication session when a user logs in successfully. The session identifier issued before authentication continues to identify the same server-side session after authentication completes. This breaks a core defense against session fixation attacks, which requires that any anonymous session be discarded and replaced once a principal is established.

The vulnerability is classified under [CWE-384: Session Fixation]. Exploitation depends on the attacker convincing or tricking a victim into using a session identifier that the attacker already knows. Common vectors include phishing links that set a JSESSIONID cookie, cross-site cookie injection on shared domains, or network paths where session identifiers traverse insecure channels. Once the victim authenticates, the attacker replays the known identifier and inherits the authenticated context.

Root Cause

The root cause is missing session lifecycle hygiene in Shiro's default login flow. On successful authentication, the framework neither invalidates the existing Session object nor rotates its sessionId. The implementation does not call the equivalent of session migration logic before establishing the authenticated Subject.

Attack Vector

The attack vector is network-based and requires user interaction. The attacker first obtains a valid pre-authentication session identifier from the target application, then plants that identifier in the victim's browser through cookie injection, a crafted URL, or a man-in-the-middle position. When the victim authenticates against the Shiro-protected application, the same session identifier remains valid and is now bound to the authenticated principal. The attacker uses the identifier to issue requests as the victim.

No verified public exploit code is available at the time of publication. See the Apache Shiro Security Report and the Openwall OSS-Security Discussion for vendor details.

Detection Methods for CVE-2026-43827

Indicators of Compromise

• Identical JSESSIONID or Shiro session cookie values observed in HTTP traffic both before and after a successful authentication event for the same user.
• Concurrent use of the same session identifier from different source IP addresses, user agents, or geolocations.
• Authentication success log entries that are not paired with a session identifier rotation in application logs.

Detection Strategies

• Instrument the application to log session identifiers at login and compare pre- and post-authentication values; flag cases where the identifier does not change.
• Correlate web access logs with authentication events to identify sessions whose identifier predates the login event by an unusual margin.
• Deploy web application firewall rules that detect session cookies being set via query strings or third-party origins before a login request.

Monitoring Recommendations

• Forward Shiro and application server logs into a centralized analytics platform and alert on session identifier reuse across authentication state transitions.
• Monitor for anomalies such as a single session identifier authenticating multiple accounts within a short window.
• Track inventory of Java applications using Apache Shiro 1.x, 2.0.x, 2.1.0, or 3.0.0-alpha-1 to prioritize patching and detection coverage.

How to Mitigate CVE-2026-43827

Immediate Actions Required

• Upgrade Apache Shiro to version 2.1.1 or 3.0.0-alpha-2 or later, which invalidate the prior session and issue a new identifier on login.
• Inventory all applications, frameworks, and libraries that bundle Apache Shiro, including transitive Maven and Gradle dependencies.
• Force logout and session reset for all active users after deploying the patch to evict any pre-existing fixated sessions.

Patch Information

The Apache Shiro project addressed CVE-2026-43827 in releases 2.1.1 and 3.0.0-alpha-2. The fix ensures that any existing session is invalidated upon successful authentication and a new session with a fresh identifier is generated. Refer to the Apache Shiro Security Report for the authoritative advisory and release notes.

Workarounds

• Configure the application to manually invalidate the current Subject session and call subject.getSession(true) immediately after subject.login() so a new session identifier is issued.
• Set the Secure and HttpOnly attributes on session cookies and restrict the SameSite attribute to Lax or Strict to reduce cross-site cookie planting.
• Disable URL-based session identifiers (for example, ;jsessionid= rewriting) in the servlet container to remove a common fixation vector.

# Example Maven dependency update to patched Apache Shiro release
# Replace existing shiro-core dependency with the fixed version
mvn versions:set-property -Dproperty=shiro.version -DnewVersion=2.1.1
mvn dependency:tree | grep shiro