CVE-2025-20363 Overview
A critical heap-based buffer overflow vulnerability exists in the web services of multiple Cisco networking products, including Cisco Secure Firewall Adaptive Security Appliance (ASA) Software, Cisco Secure Firewall Threat Defense (FTD) Software, Cisco IOS Software, Cisco IOS XE Software, and Cisco IOS XR Software. This vulnerability allows an unauthenticated, remote attacker (for ASA and FTD) or an authenticated, remote attacker with low privileges (for IOS, IOS XE, and IOS XR) to execute arbitrary code on affected devices.
The vulnerability stems from improper validation of user-supplied input in HTTP requests. Successful exploitation enables attackers to execute arbitrary code as root, potentially leading to complete compromise of the affected device.
Critical Impact
Remote code execution with root privileges allowing complete device takeover of critical network infrastructure including firewalls and routers.
Affected Products
- Cisco Secure Firewall Adaptive Security Appliance (ASA) Software
- Cisco Secure Firewall Threat Defense (FTD) Software
- Cisco IOS Software
- Cisco IOS XE Software
- Cisco IOS XR Software (versions 6.5.x through 6.9.x)
- Cisco ASR 9001 Series Routers
Discovery Timeline
- September 25, 2025 - CVE-2025-20363 published to NVD
- February 10, 2026 - Last updated in NVD database
Technical Details for CVE-2025-20363
Vulnerability Analysis
This vulnerability is classified as CWE-122 (Heap-based Buffer Overflow), a memory corruption vulnerability that occurs when data is written beyond the allocated buffer boundaries in the heap memory. The flaw exists in the HTTP request handling mechanism of affected Cisco web services, where user-supplied input is not properly validated before being processed.
The attack requires network access to the device's web services interface. For Cisco ASA and FTD Software, no authentication is required, making these products particularly susceptible to exploitation. For Cisco IOS, IOS XE, and IOS XR Software, an attacker must first obtain low-privilege authentication credentials before attempting exploitation.
Successful exploitation requires the attacker to obtain additional information about the target system or overcome exploit mitigations. Once these prerequisites are met, the attacker can achieve arbitrary code execution with root privileges, providing full control over the affected device.
Root Cause
The root cause of CVE-2025-20363 is improper validation of user-supplied input in HTTP requests processed by the web services component. When specially crafted HTTP requests are sent to the vulnerable service, the lack of boundary checking allows data to overflow into adjacent heap memory regions. This heap-based buffer overflow can corrupt memory structures, potentially allowing an attacker to control program execution flow and inject malicious code.
Attack Vector
The attack vector is network-based, targeting the web services interface exposed by affected Cisco devices. An attacker would craft malicious HTTP requests containing oversized or specially formatted input designed to trigger the buffer overflow condition. The attack sequence involves:
- Identifying a target device running vulnerable software with web services enabled
- Gathering system information or identifying techniques to bypass exploit mitigations
- Sending crafted HTTP requests to the web services endpoint
- Exploiting the heap overflow to achieve code execution with root privileges
- Gaining complete control of the network device
For technical details on exploitation, refer to the Cisco Security Advisory.
Detection Methods for CVE-2025-20363
Indicators of Compromise
- Unusual or malformed HTTP requests targeting device management interfaces
- Unexpected process crashes or restarts of web services components
- Unauthorized configuration changes or new user accounts on network devices
- Anomalous outbound connections from network infrastructure devices
- Evidence of code execution or shell access from web service processes
Detection Strategies
- Deploy network intrusion detection systems (IDS) to monitor for anomalous HTTP traffic patterns targeting Cisco device management interfaces
- Enable comprehensive logging on affected devices and monitor for authentication failures, unusual web service activity, or unexpected privilege escalations
- Implement deep packet inspection to identify malformed HTTP requests with oversized payloads targeting vulnerable services
- Monitor device integrity using file integrity monitoring solutions to detect unauthorized modifications
Monitoring Recommendations
- Configure SIEM rules to alert on suspicious HTTP activity targeting Cisco ASA, FTD, IOS, IOS XE, and IOS XR web services
- Establish baseline network behavior for management interfaces and alert on deviations
- Monitor for unexpected process behavior or memory utilization spikes on affected devices
- Implement continuous vulnerability scanning to identify unpatched systems in your environment
How to Mitigate CVE-2025-20363
Immediate Actions Required
- Review the Cisco Security Advisory for specific patch versions and apply appropriate updates immediately
- Disable web services on affected devices if not required for operations
- Restrict access to management interfaces using access control lists (ACLs) to trusted networks only
- Implement network segmentation to isolate management plane traffic from untrusted networks
Patch Information
Cisco has released security patches to address this vulnerability. Administrators should consult the Cisco Security Advisory for specific fixed software versions applicable to their deployment. Given the critical severity and potential for unauthenticated remote code execution on ASA and FTD platforms, immediate patching is strongly recommended.
For Cisco IOS XR systems, affected versions include 6.5.1 through 6.9.2. Organizations should upgrade to the latest patched release as specified in the vendor advisory.
Workarounds
- Disable HTTP and HTTPS server functionality on affected devices if not operationally required
- Implement strict access control lists to limit web services access to trusted management networks only
- Deploy web application firewalls or reverse proxies to filter malicious HTTP requests before they reach vulnerable devices
- Consider using out-of-band management networks to isolate device management traffic from production networks
# Example: Disable HTTP server on Cisco IOS/IOS XE devices
configure terminal
no ip http server
no ip http secure-server
exit
write memory
# Example: Restrict management access with ACL
ip access-list extended MGMT-ACCESS
permit tcp 10.0.0.0 0.0.0.255 any eq 443
deny tcp any any eq 443 log
deny tcp any any eq 80 log
exit
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
