CVE-2026-25690 Overview
CVE-2026-25690 is an argument injection vulnerability affecting multiple versions of Fortinet FortiDeceptor. The flaw exists in the product's handling of HTTP requests, where argument delimiters in commands are not properly neutralized [CWE-88]. An authenticated attacker holding at least read-only administrative permissions can craft HTTP requests to read log files on the affected appliance. The vulnerability requires valid credentials and exposes information stored in system log files. Fortinet documented the issue in advisory FG-IR-26-138.
Critical Impact
An authenticated attacker with read-only admin access can read arbitrary log files on FortiDeceptor appliances by injecting argument delimiters into HTTP requests.
Affected Products
- Fortinet FortiDeceptor 6.0.0 through 6.0.2
- Fortinet FortiDeceptor 5.3.0 through 5.3.3, 5.2.0 through 5.2.1
- Fortinet FortiDeceptor 5.1 all versions, 5.0 all versions
Discovery Timeline
- 2026-05-12 - CVE CVE-2026-25690 published to NVD
- 2026-05-12 - Last updated in NVD database
Technical Details for CVE-2026-25690
Vulnerability Analysis
The vulnerability is classified under [CWE-88] Improper Neutralization of Argument Delimiters in a Command, commonly known as argument injection. FortiDeceptor accepts HTTP parameters that are passed into a backend command without sanitizing characters used as argument separators. An attacker authenticated to the management interface can supply parameters that introduce additional arguments to the underlying command. The injected arguments influence the behavior of the log-reading routine, allowing unauthorized retrieval of log file contents. The attack requires network access to the management interface and at least read-only administrator credentials.
Root Cause
The root cause is the absence of strict input validation on HTTP parameters consumed by a log-handling command. The application concatenates user-supplied input into a command invocation without escaping delimiters such as whitespace, hyphens, or option separators. As a result, attacker-supplied tokens are interpreted as command-line flags rather than data values. This permits a low-privilege admin to expand the command's scope beyond its intended targets.
Attack Vector
The attack vector is network-based through the FortiDeceptor management interface. The attacker authenticates with a read-only admin account, then issues an HTTP request containing crafted parameter values that include argument delimiters. The backend executes the resulting command with the injected flags, returning log file contents in the response. Confidentiality of log data is impacted; integrity and availability are not affected. See the Fortinet Security Advisory FG-IR-26-138 for vendor technical details.
Detection Methods for CVE-2026-25690
Indicators of Compromise
- HTTP requests to the FortiDeceptor management interface containing argument delimiter characters such as -, --, or whitespace within parameter values.
- Unexpected log file read activity associated with read-only administrator accounts.
- Audit log entries showing log access actions initiated by accounts that do not normally interact with log data.
Detection Strategies
- Inspect FortiDeceptor administrative audit logs for HTTP requests whose query parameters contain shell-style flag syntax.
- Correlate read-only admin sessions with bulk or repeated log retrieval operations.
- Apply web application firewall rules that flag argument-injection patterns submitted to the management endpoint.
Monitoring Recommendations
- Forward FortiDeceptor administrative and access logs to a centralized SIEM for retention and correlation.
- Alert on authentication events for read-only admin accounts followed by parameter-heavy HTTP POST or GET requests.
- Baseline normal administrator API usage and trigger anomalies when parameter content deviates from expected schemas.
How to Mitigate CVE-2026-25690
Immediate Actions Required
- Upgrade FortiDeceptor to a fixed release as identified in advisory FG-IR-26-138.
- Audit all administrator accounts and remove unnecessary read-only admin privileges.
- Restrict network access to the FortiDeceptor management interface to trusted administrative networks only.
- Rotate credentials for any administrator account that may have been exposed.
Patch Information
Fortinet has published remediation guidance in advisory FG-IR-26-138. Administrators should consult the Fortinet Security Advisory FG-IR-26-138 to confirm the fixed version applicable to their deployment and upgrade affected FortiDeceptor 5.0, 5.1, 5.2, 5.3, and 6.0 instances accordingly.
Workarounds
- Limit management interface exposure using firewall access lists that permit only trusted administrative IP ranges.
- Enforce the principle of least privilege by reducing the number of accounts with admin-level access, including read-only roles.
- Enable multi-factor authentication on all administrative accounts to raise the bar for credential abuse.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
