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Denial of Service Vulnerability in CISCO 

Indian – Computer Emergency Response Team (https://www.cert-in.org.in)

Severity Rating: HIGH

Software Affected

Cisco Secure Firewall ASA Software and Cisco Secure FTD Software

Overview

Multiple vulnerabilities have been reported in Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software could allow an authenticated, remote attacker to create or delete arbitrary files on the underlying operating system, buffer overflow and consume resources that are associated with incoming TLS 1.3 connections, which eventually could cause the device to stop accepting any new SSL/TLS or VPN requests.

Target Audience: 

All IT administrators and individuals responsible for maintaining and updating Cisco Secure Firewall ASA Software and Secure FTD Software.

Risk Assessment:

High risk of data manipulation and service disruption.

Impact Assessment:

Potential impact on confidentiality, integrity, and availability of the system.

Description

1. VPN Web Server Denial of Service Vulnerability ( CVE-2025-20251   )

This vulnerability exists due to insufficient input validation when processing HTTP requests. An attacker could exploit this vulnerability by sending crafted HTTP requests to an affected device.

Successful exploitation of this vulnerability could allow the attacker to create or delete files on the underlying operating system, which could cause the Remote Access SSL VPN service to become unresponsive.

2. Web Services Denial of Service Vulnerability ( CVE-2025-20263   )

This vulnerability exists due to insufficient boundary checks for specific data that is provided to the web services interface of an affected system. An attacker could exploit this vulnerability by sending a crafted HTTP request to the affected system.

Successful exploitation of this vulnerability could allow the attacker to cause a buffer overflow condition on the affected system, which could cause the system to reload, resulting in a denial of service (DoS) condition.

3. FirePower 3100 and 4200 Series TLS 1.3 Cipher Denial of Service Vulnerability ( CVE-2025-20127   )

This vulnerability exists due to the implementation of the TLS 1.3 Cipher TLS_CHACHA20_POLY1305_SHA256. An attacker could exploit this vulnerability by sending a large number of TLS 1.3 connections with the specific TLS 1.3 Cipher TLS_CHACHA20_POLY1305_SHA256.

Successful exploitation of this vulnerability could allow the attacker to cause a denial of service (DoS) condition where no new incoming encrypted connections are accepted.

Note: These incoming TLS 1.3 connections include both data traffic and user-management traffic. After the device is in the vulnerable state, no new encrypted connections can be accepted.

Solution

Apply appropriate updates as mentioned in Cisco Advisory

https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-http-file-hUyX2jL4

https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asa-buffer-overflow-PyRUhWBC

https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-3100_4200_tlsdos-2yNSCd54

Vendor Information

CISCO

https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-http-file-hUyX2jL4

https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asa-buffer-overflow-PyRUhWBC

https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-3100_4200_tlsdos-2yNSCd54

References

CISCO

https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-http-file-hUyX2jL4

https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asa-buffer-overflow-PyRUhWBC

https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-3100_4200_tlsdos-2yNSCd54

CVE Name

CVE-2025-20251

CVE-2025-20263

CVE-2025-20127

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Thanks and Regards,

CERT-In

Incident Response Help Desk

e-mail: incident@cert-in.org.in

Phone: +91-11-22902657

Toll Free Number: 1800-11-4949

Toll Free Fax : 1800-11-6969

Web: http://www.cert-in.org.in

PGP Fingerprint: A768 083E 4475 5725 B81A A379 2156 C0C0 B620 D0B4

PGP Key information:

https://www.cert-in.org.in/s2cMainServlet?pageid=CONTACTUS

Postal address:

Indian Computer Emergency Response Team (CERT-In)

Ministry of Electronics and Information Technology

Government of India

Electronics Niketan

6, C.G.O. Complex

New Delhi-110 003

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