Technical details regarding a maximum-severity arbitrary file upload flaw affecting Cisco IOS XE Software for Wireless LAN Controllers, tracked as CVE-2025-20188, have been publicly released, significantly increasing the risk of exploitation. This critical vulnerability allows unauthenticated remote attackers to upload files and execute arbitrary commands with root privileges if the ‘Out-of-Band AP Image Download’ feature is enabled. Security researchers’ detailed analysis provides insights into how the flaw works and how it could be leveraged for remote code execution.
Contents
Understanding the Cisco Vulnerability
What Happened?
Cisco first disclosed this vulnerability on May 7, 2025. The flaw, identified as CVE-2025-20188, resides in the IOS XE Software specifically designed for Wireless LAN Controllers (WLC). It stems from a hard-coded JSON Web Token (JWT) secret combined with insufficient validation checks. This allows an attacker who does not need to authenticate to the system to upload files to unintended locations using directory path traversal techniques.
Severity and Impact
Rated as maximum severity, this vulnerability poses a significant risk. A successful exploit grants the attacker the ability to execute arbitrary commands with root privileges on the affected device, essentially allowing them to take complete control. The vulnerability is only exploitable when the ‘Out-of-Band AP Image Download’ feature is active on the device.
Affected Cisco Wireless LAN Controller models include:
- Catalyst 9800-CL Wireless Controllers for Cloud
- Catalyst 9800 Embedded Wireless Controller for Catalyst 9300, 9400, and 9500 Series Switches
- Catalyst 9800 Series Wireless Controllers
- Embedded Wireless Controller on Catalyst APs
Technical Analysis and Exploitation Risk
Researcher Findings
Security researchers at Horizon3 published an in-depth analysis detailing the technical aspects of CVE-2025-20188. Their analysis revealed that the vulnerability is rooted in a hard-coded JWT fallback secret, the string “notfound”, used by backend Lua scripts on upload endpoints. These scripts, utilizing OpenResty (Lua + Nginx), handle JWT validation and file uploads. If a specific file (/tmp/nginx_jwt_key) is missing, the script defaults to using “notfound” as the secret for verifying JWTs.
This fallback mechanism enables attackers to generate valid JWTs for authentication bypass simply by using the ‘HS256’ algorithm and the ‘notfound’ secret, without needing to know any legitimate secrets.
How Exploitation Works
Horizon3’s analysis demonstrated an attack scenario where an attacker sends an HTTP POST request containing a file upload to the vulnerable /ap_spec_rec/upload/ endpoint, typically on port 8443. By using path traversal within the filename parameter, an attacker can upload files outside the intended directory, such as dropping a simple text file (foo.txt).
Cisco logo representing the company impacted by the IOS XE WLC security vulnerability
Escalating this arbitrary file upload vulnerability to remote code execution involves finding ways to make the device execute the uploaded content. Potential methods include overwriting configuration files that are loaded by system services, planting web shells in accessible directories, or manipulating files that are monitored by services to trigger unauthorized actions. Horizon3 illustrated this by showing how an attacker could abuse the pvp.sh service, which monitors specific directories and reloads configuration files, to trigger the execution of attacker-controlled commands after overwriting its dependencies.
Diagram illustrating HTTP request using 'notfound' secret key to exploit Cisco IOS XE WLC file upload vulnerability
Why This Matters Now
The public availability of technical details significantly increases the likelihood that threat actors will develop and use working exploits for CVE-2025-20188. This makes it critical for affected organizations to take immediate action to secure their vulnerable devices.
Recommendations and Mitigation
Given the severity and increased risk of exploitation, Cisco strongly recommends applying security updates.
Applying Patches
The primary recommendation is to upgrade the Cisco IOS XE Software for Wireless LAN Controllers to a patched version. Cisco advises users to upgrade to version 17.12.04 or a newer release that addresses this vulnerability.
Temporary Workaround
If immediate patching is not possible, administrators can mitigate the risk by disabling the ‘Out-of-Band AP Image Download’ feature. This action closes the specific service that is vulnerable to exploitation by attackers.
Users should prioritize assessing their environments for affected devices and implementing the recommended patches or workaround as soon as possible to protect against potential attacks.
Stay informed on the latest cybersecurity threats and vulnerabilities impacting network infrastructure. You can explore related articles on topics like exploits targeting vBulletin forum software or critical unpatched bugs in Versa Concerto leading to RCE to understand the broader threat landscape.
