Introduction
Remote attackers can gain control over Linksys RE6250, RE6300, RE6350, RE6500, RE7000, and RE9000 wireless range extenders by exploiting a stack-based buffer overflow in their web management interface. This vulnerability, tracked as CVE-2025-8833, affects devices running firmware up to 20250801 and remains unpatched due to a lack of vendor response. With public exploit code available, these devices are exposed to remote takeover, configuration tampering, and use as a foothold for further attacks on internal networks.
Linksys is a leading global provider of consumer and small business networking equipment, with millions of devices deployed worldwide. Their RE series range extenders are widely used to improve wireless coverage in homes and offices. The security posture of these products has a direct impact on the integrity of countless networks.
Technical Information
CVE-2025-8833 is a stack-based buffer overflow vulnerability in the langSwitchBack function of Linksys RE series range extenders. The flaw is exposed via the /goform/langSwitchBack HTTP endpoint, which handles language selection for the device's web interface. The vulnerability is triggered when an attacker sends a POST request with an excessively long langSelectionOnly parameter. The firmware fails to check the length of this parameter before copying it into a fixed-size stack buffer, leading to memory corruption.
The root cause is unsafe input handling in C-based firmware. Specifically, the code does not validate the size of user-supplied input before copying it to a stack-allocated buffer. This allows an attacker to overwrite adjacent memory, including the function's return address, enabling arbitrary code execution.
This vulnerability is similar to several other recent flaws in Linksys RE series devices, including:
- 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 issues stem from a lack of proper 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 a stack-based buffer overflow vulnerability in Linksys range extenders, specifically models RE6250, RE6300, RE6350, RE6500, RE7000, and RE9000, up to firmware version 20250801. This vulnerability resides in the langSwitchBack function of the /goform/langSwitchBack endpoint, where the langSelectionOnly parameter is susceptible to manipulation.
By sending a specially crafted HTTP request with an excessively long langSelectionOnly parameter, an attacker can overflow the stack buffer, potentially leading to arbitrary code execution. This exploit can be initiated remotely, allowing unauthenticated attackers to compromise the device over the network.
The exploit involves crafting an HTTP POST request to the vulnerable endpoint with the langSelectionOnly parameter containing a payload designed to overflow the buffer. Successful exploitation could grant the attacker control over the device, enabling actions such as altering configurations, intercepting network traffic, or deploying further attacks within the network.
It's important to note that the vendor was contacted regarding this vulnerability but did not respond, leaving the devices unpatched and vulnerable 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
All configurations with the web management interface enabled are vulnerable.
Vendor Security History
Linksys has a history of similar vulnerabilities in their RE series range extenders. Recent issues 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 multiple cases, researchers reported that Linksys did not respond to coordinated disclosure attempts. No patches or advisories have been released for several of these critical vulnerabilities, indicating a poor security response track record.