Introduction
Remote attackers can take over Linksys RE6250, RE6300, RE6350, RE6500, RE7000, and RE9000 wireless range extenders through a stack-based buffer overflow in their web management interface. The vulnerability, tracked as CVE-2025-8833, affects devices running firmware up to 20250801. It is unpatched because the vendor did not respond. Public exploit code is available, so these devices are open to remote takeover, configuration tampering, and use as a foothold for further attacks on internal networks.
Linksys sells consumer and small business networking equipment, and its RE series range extenders are common in homes and offices for extending wireless coverage. The security of these products affects the networks they sit on.
Technical Information
CVE-2025-8833 is a stack-based buffer overflow in the langSwitchBack function of Linksys RE series range extenders. The flaw is reachable through the /goform/langSwitchBack HTTP endpoint, which handles language selection for the device's web interface. It triggers when an attacker sends a POST request with an overlong langSelectionOnly parameter. The firmware does not check the length of this parameter before copying it into a fixed-size stack buffer, which corrupts memory.
The root cause is unsafe input handling in C-based firmware. The code copies user-supplied input into a stack-allocated buffer without checking its size. That lets an attacker overwrite adjacent memory, including the function's return address, which can lead to arbitrary code execution.
This matches several other recent flaws in Linksys RE series devices:
- CVE-2025-8819 (stack buffer overflow in setWan via staticIp)
- CVE-2025-8816 (stack buffer overflow in setOpMode via ethConv)
- CVE-2025-8817 (stack buffer overflow in setLan via lan2enabled)
- CVE-2025-8822 (stack buffer overflow in algDisable via opMode)
All of these come from missing input validation and bounds checking in the device's HTTP request handlers.
Proof of Concept
The proof-of-concept (PoC) exploit for CVE-2025-8833 targets the stack-based buffer overflow in Linksys range extenders, specifically models RE6250, RE6300, RE6350, RE6500, RE7000, and RE9000, up to firmware version 20250801. The flaw is in the langSwitchBack function of the /goform/langSwitchBack endpoint, where the langSelectionOnly parameter can be manipulated.
By sending a crafted HTTP request with an overlong langSelectionOnly parameter, an attacker can overflow the stack buffer, which can lead to arbitrary code execution. The attack works remotely, so an unauthenticated attacker can compromise the device over the network.
The exploit uses an HTTP POST request to the vulnerable endpoint, with the langSelectionOnly parameter carrying a payload that overflows the buffer. A successful attack can grant control over the device, allowing the attacker to change configurations, intercept network traffic, or stage further attacks inside the network.
The vendor was contacted about this vulnerability but did not respond, so the devices remain unpatched and exposed to this exploit.
PoC reference: yanac.hu CVE-2025-8833 writeup
Affected Systems and Versions
- Linksys RE6250: firmware up to 20250801
- Linksys RE6300: firmware up to 20250801
- Linksys RE6350: firmware up to 20250801
- Linksys RE6500: firmware up to 20250801
- Linksys RE7000: firmware up to 20250801
- Linksys RE9000: firmware up to 20250801
Any configuration with the web management interface enabled is vulnerable.
Vendor Security History
Linksys has a record of similar vulnerabilities in its RE series range extenders. Recent ones include:
- CVE-2025-8819: stack buffer overflow in setWan
- CVE-2025-8816: stack buffer overflow in setOpMode
- CVE-2025-8817: stack buffer overflow in setLan
- CVE-2025-8822: stack buffer overflow in algDisable
In several of these cases, researchers reported that Linksys did not respond to coordinated disclosure. No patches or advisories have been released for several of these critical vulnerabilities.
