CVE-2026-26035 Overview
CVE-2026-26035 is an Improper Authentication vulnerability [CWE-287] affecting multiple versions of Fortinet FortiWeb. The flaw allows a remote unauthenticated attacker to log into the FortiWeb GUI or CLI using an arbitrary username and password. Successful exploitation grants administrative access to the web application firewall, exposing protected applications and configuration data.
Critical Impact
A network-based attacker can bypass authentication on FortiWeb management interfaces without credentials, gaining full control of the appliance and the ability to modify security policies protecting downstream web applications.
Affected Products
- Fortinet FortiWeb 8.0.0 through 8.0.2
- Fortinet FortiWeb 7.6.0 through 7.6.6, 7.4.0 through 7.4.11
- Fortinet FortiWeb 7.2.0 through 7.2.12, 7.0.0 through 7.0.12
Discovery Timeline
- 2026-08-12 - CVE-2026-26035 published to NVD
- 2026-08-13 - Last updated in NVD database
Technical Details for CVE-2026-26035
Vulnerability Analysis
CVE-2026-26035 is an authentication bypass in the FortiWeb management plane. The vulnerability allows attackers to authenticate to both the graphical user interface (GUI) and command-line interface (CLI) using a random username and password combination. No prior credentials, tokens, or user interaction are required.
FortiWeb functions as a web application firewall protecting production web applications. Administrative access to the appliance therefore extends beyond the device itself. An attacker can disable protections, alter routing, exfiltrate SSL/TLS keys stored on the appliance, or pivot into internal networks the appliance reaches.
Root Cause
The root cause is improper authentication logic [CWE-287] in the FortiWeb authentication handler. According to the Fortinet PSIRT Advisory FG-IR-26-158, the authentication routine fails to correctly validate submitted credentials, permitting login with arbitrary values. Vendor advisory content is the definitive source for the specific code path.
Attack Vector
The attack vector is network-based and requires no authentication or user interaction. An attacker with network reachability to the FortiWeb management interface submits a login request to the GUI (HTTPS) or CLI (SSH) endpoint using any username and password. The service accepts the request and issues an authenticated session. Appliances with management interfaces exposed to the internet face the highest risk.
Detection Methods for CVE-2026-26035
Indicators of Compromise
- Successful administrative logins from unexpected source IP addresses or geographies in FortiWeb audit logs.
- New or modified administrator accounts, policies, or SSL/TLS certificates that do not match change-management records.
- Session activity for usernames that do not exist in the identity directory or local user database.
Detection Strategies
- Correlate FortiWeb event.log entries for successful GUI and CLI logins against known administrator identities and source networks.
- Alert on any successful login from a source address not on the management access allow-list.
- Baseline configuration snapshots and alert on unexpected diffs to policies, users, or listener configuration.
Monitoring Recommendations
- Forward FortiWeb authentication and configuration-change logs to a centralized SIEM for retention and correlation.
- Monitor outbound connections from FortiWeb appliances for unexpected destinations that may indicate post-exploitation activity.
- Review scheduled tasks, backup exports, and API token creation events on the appliance daily during the remediation window.
How to Mitigate CVE-2026-26035
Immediate Actions Required
- Restrict access to the FortiWeb GUI and CLI management interfaces to trusted management networks using firewall rules or trusted hosts configuration.
- Remove any exposure of the FortiWeb management interface to the public internet.
- Rotate all administrator credentials, API keys, and certificates stored on the appliance after patching.
- Audit administrator accounts, policies, and recent configuration changes for unauthorized modifications.
Patch Information
Refer to the Fortinet PSIRT Advisory FG-IR-26-158 for fixed version details and upgrade guidance. Administrators should upgrade FortiWeb 8.0.x, 7.6.x, 7.4.x, 7.2.x, and 7.0.x branches to the fixed releases specified by Fortinet.
Workarounds
- Disable HTTP/HTTPS administrative access on internet-facing interfaces until patching is complete.
- Enforce trusted hosts on all administrator accounts to limit login sources to specific management IP ranges.
- Place the FortiWeb management interface behind a VPN or bastion host that requires strong multi-factor authentication.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
