CVE-2025-8826: Linksys Re6250 Buffer Overflow Vulnerability

CVE-2025-8826 Overview

CVE-2025-8826 is a stack-based buffer overflow [CWE-119] affecting multiple Linksys range extender models, including the RE6250, RE6300, RE6350, RE6500, RE7000, and RE9000 firmware up to build 20250801. The flaw resides in the um_rp_autochannel function inside the /goform/RP_setBasicAuto handler. An authenticated remote attacker can trigger memory corruption by manipulating the apcli_AuthMode_2G or apcli_AuthMode_5G parameters. The exploit details have been disclosed publicly, and Linksys did not respond to early disclosure attempts.

Critical Impact

Successful exploitation can corrupt stack memory on the device, leading to denial of service or arbitrary code execution within the router's web management process.

Affected Products

• Linksys RE6250 firmware 1.0.04.001 and RE6300 firmware 1.2.07.001
• Linksys RE6350 firmware 1.0.04.001 and RE6500 firmware 1.0.013.001
• Linksys RE7000 firmware 1.1.05.003 and RE9000 firmware 1.0.04.002

Discovery Timeline

• 2025-08-11 - CVE-2025-8826 published to NVD
• 2025-09-04 - Last updated in NVD database

Technical Details for CVE-2025-8826

Vulnerability Analysis

The vulnerability exists in the um_rp_autochannel function, which processes range extender auto-channel configuration requests submitted to the /goform/RP_setBasicAuto endpoint. The handler reads attacker-controlled values from the apcli_AuthMode_2G and apcli_AuthMode_5G HTTP parameters and copies them into a fixed-size stack buffer without enforcing length validation. Oversized inputs overflow adjacent stack memory, including saved return addresses and frame pointers.

The flaw is reachable over the network and requires only low privileges, matching the credentials typically used to access the device's web interface. Public disclosure of exploit details increases the likelihood of opportunistic attacks against exposed extenders. EPSS data places the probability of exploitation at 0.871%.

Root Cause

The root cause is missing bounds checking when copying user-supplied authentication mode parameters into a stack-allocated buffer inside um_rp_autochannel. The code path trusts the length of HTTP form data submitted through the /goform/RP_setBasicAuto interface, which permits writes beyond the buffer boundary and corrupts the call stack.

Attack Vector

An attacker who can reach the device's HTTP management interface, typically on the LAN or via an exposed remote management port, submits a crafted POST request to /goform/RP_setBasicAuto containing an overlong value in apcli_AuthMode_2G or apcli_AuthMode_5G. The malformed request reaches um_rp_autochannel, which performs the unsafe copy and overflows the stack. Depending on memory layout and protections on the MIPS or ARM firmware build, the attacker can crash the service or hijack control flow to execute arbitrary code. Detailed proof-of-concept material is available in the public vulnerability report.

No verified exploit code is reproduced here. Refer to the GitHub PoC repository and VulDB entry #319360 for technical details.

Detection Methods for CVE-2025-8826

Indicators of Compromise

• HTTP POST requests targeting /goform/RP_setBasicAuto with abnormally long apcli_AuthMode_2G or apcli_AuthMode_5G parameter values.
• Unexpected reboots, watchdog resets, or httpd process crashes on Linksys RE-series extenders.
• New or modified administrative sessions originating from untrusted source IP addresses targeting the extender management interface.

Detection Strategies

• Inspect web traffic to range extenders for parameter values exceeding expected authentication mode string lengths (typically short tokens such as WPA2PSK).
• Alert on repeated 5xx responses or connection resets from the /goform/RP_setBasicAuto endpoint, which indicate crash conditions.
• Correlate device availability monitoring with configuration-change events to detect post-exploitation persistence attempts.

Monitoring Recommendations

• Forward router syslog and HTTP access logs to a centralized logging platform for parameter-length and anomaly analysis.
• Track outbound connections from extender management VLANs to identify command-and-control behavior following compromise.
• Baseline normal administrative request patterns and alert on deviations targeting /goform/ URIs.

How to Mitigate CVE-2025-8826

Immediate Actions Required

• Restrict access to the extender's web management interface to trusted administrative hosts on isolated VLANs.
• Disable any remote or WAN-side management features on affected RE6250, RE6300, RE6350, RE6500, RE7000, and RE9000 devices.
• Rotate administrative credentials on all affected devices to reduce risk from the low-privilege authenticated attack path.
• Inventory deployed Linksys range extenders and identify devices running the firmware versions listed in the affected products section.

Patch Information

Linksys did not respond to the original disclosure, and no vendor patch was referenced in the advisory at the time of publication. Monitor the Linksys official site for firmware updates addressing CVE-2025-8826, and review VulDB entry #319360 for status changes.

Workarounds

• Place affected extenders behind a network segment that blocks HTTP and HTTPS access from untrusted clients.
• Replace end-of-support range extenders with currently supported hardware if no patched firmware becomes available.
• Use a web application firewall or upstream filtering rule to drop requests to /goform/RP_setBasicAuto containing oversized form fields.

# Example iptables rule restricting extender management access to a trusted host
iptables -A FORWARD -p tcp -d <extender_ip> --dport 80 -s <admin_host_ip> -j ACCEPT
iptables -A FORWARD -p tcp -d <extender_ip> --dport 80 -j DROP