CVE-2026-15579 Overview
CVE-2026-15579 is an out-of-bounds write vulnerability [CWE-787] affecting Moxa Ethernet switches. The flaw exists in the Web login processing routine, which fails to validate the length of the username field. A remote unauthenticated attacker can submit a specially crafted overly long username to trigger a buffer overflow. The overflow crashes the authentication process and results in a Denial of Service (DoS) condition on the switch management interface. Moxa published the issue in advisory MPSA-252620.
Critical Impact
Unauthenticated remote attackers can crash the authentication service of affected Moxa Ethernet switches by sending an overly long username to the Web login endpoint, disrupting device management.
Affected Products
- Moxa Ethernet switches (see vendor advisory MPSA-252620 for the specific affected models and firmware versions)
- Web management interface component responsible for login processing
- Deployments exposing switch management interfaces to untrusted networks
Discovery Timeline
- 2026-09-18 - CVE-2026-15579 published to NVD
- 2026-09-18 - Last updated in NVD database
- Vendor advisory - Moxa Security Advisory MPSA-252620
Technical Details for CVE-2026-15579
Vulnerability Analysis
The vulnerability resides in the Web-based management interface of affected Moxa Ethernet switches. During the login workflow, the server-side handler reads the submitted username field into a fixed-size buffer without enforcing a maximum length. An attacker who submits an oversized username causes the handler to write past the end of the destination buffer. The out-of-bounds write corrupts adjacent memory and terminates the authentication process. Because the flaw is reachable pre-authentication on the network-facing management interface, any attacker with reachability to the Web UI can trigger it.
Root Cause
The root cause is improper input length validation [CWE-787] in the Web login processing code path. The handler trusts the client-supplied username size and copies the data into a stack or heap buffer of insufficient capacity. Missing bounds checks allow attacker-controlled bytes to overwrite adjacent memory structures, producing a crash.
Attack Vector
The attack vector is network-based and requires no privileges or user interaction. An attacker sends a crafted HTTP or HTTPS POST request to the switch's Web login endpoint with a username field containing an overly long string. The malformed request reaches the vulnerable parser before authentication checks complete. The authentication process crashes, denying legitimate administrators access to the Web management interface until the service or device restarts. See the Moxa Security Advisory MPSA-252620 for confirmed impact details.
Detection Methods for CVE-2026-15579
Indicators of Compromise
- Unexpected restarts or crashes of the Web management daemon on Moxa switches
- HTTP or HTTPS POST requests to the login endpoint containing abnormally long username parameter values
- Loss of Web UI availability while other switch functions such as data-plane forwarding remain operational
- Repeated failed connection attempts to the management interface from a single source IP
Detection Strategies
- Inspect Web server and management logs for oversized username fields or malformed login POST bodies
- Deploy network IDS or WAF signatures that flag login requests with username parameters exceeding expected length limits
- Correlate management-plane crash events with recent inbound HTTP traffic to identify probable exploitation attempts
Monitoring Recommendations
- Enable syslog forwarding from Moxa switches to a central log platform and alert on authentication service restarts
- Monitor for connectivity loss to the switch management interface using scheduled availability checks
- Track access to switch management IPs from unexpected source networks or geographies
How to Mitigate CVE-2026-15579
Immediate Actions Required
- Restrict access to the Web management interface to a dedicated management VLAN and trusted administrator hosts only
- Block inbound HTTP and HTTPS to switch management IPs at perimeter and internal firewalls
- Apply the vendor firmware update as soon as it is available for your specific switch model
- Inventory all deployed Moxa Ethernet switches and verify firmware versions against the vendor advisory
Patch Information
Moxa published advisory MPSA-252620 covering this issue. Consult the Moxa Security Advisory MPSA-252620 for the list of affected models, fixed firmware versions, and vendor-recommended remediation steps.
Workarounds
- Disable the Web management interface where it is not required and manage the switch through the console port or SSH
- Place switch management interfaces on an isolated out-of-band management network unreachable from user or internet segments
- Enforce ACLs on the switch to allow management connections only from specific administrator source addresses
- Rate-limit or filter HTTP requests to the login endpoint using an upstream reverse proxy or firewall
# Example: restrict access to the switch management interface using an upstream firewall (iptables)
# Replace 10.0.0.0/24 with your management subnet and 192.0.2.10 with the switch IP
iptables -A FORWARD -s 10.0.0.0/24 -d 192.0.2.10 -p tcp --dport 443 -j ACCEPT
iptables -A FORWARD -s 10.0.0.0/24 -d 192.0.2.10 -p tcp --dport 80 -j ACCEPT
iptables -A FORWARD -d 192.0.2.10 -p tcp --dport 443 -j DROP
iptables -A FORWARD -d 192.0.2.10 -p tcp --dport 80 -j DROP
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
