Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software for Firepower 3100 and 4200 Series TLS Cipher Denial of Service Vulnerability

Summary

CVE	CVE-2025-20127
State	PUBLISHED
Assigner	cisco
Source Priority	CVE Program / NVD first with legacy fallback
Published	2025-08-14 17:15:33 UTC
Updated	2026-08-11 19:33:44 UTC
Description	A vulnerability in the TLS 1.3 implementation for a specific cipher for Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software for Cisco Firepower 3100 and 4200 Series devices could allow an authenticated, remote attacker to 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. This vulnerability is 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. A successful exploit could allow the attacker to cause a denial of service (DoS) condition where no new incoming encrypted connections are accepted. The device must be reloaded to clear this condition. 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.

Risk And Classification

Primary CVSS: v3.1 7.7 HIGH from [email protected]

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H

Problem Types: CWE-404 | CWE-404 Improper Resource Shutdown or Release

Version	Source	Type	Score	Severity	Vector
3.1	[email protected]	Secondary	7.7	HIGH	`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H`
3.1	CNA	CVSSV3_1	7.7	HIGH	`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H`

CVSS v3.1 Breakdown

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Changed

Confidentiality

None

Integrity

None

Availability

High

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H

NVD Known Affected Configurations (CPE 2.3)

Type	Vendor	Product	Version	Update	Edition	Language
Operating System	Cisco	Adaptive Security Appliance Software	9.20.1	All	All	All
Operating System	Cisco	Adaptive Security Appliance Software	9.20.1.5	All	All	All
Operating System	Cisco	Adaptive Security Appliance Software	9.20.2	All	All	All
Operating System	Cisco	Adaptive Security Appliance Software	9.20.2.10	All	All	All
Operating System	Cisco	Adaptive Security Appliance Software	9.20.2.21	All	All	All
Operating System	Cisco	Adaptive Security Appliance Software	9.20.2.22	All	All	All
Operating System	Cisco	Adaptive Security Appliance Software	9.20.3	All	All	All
Operating System	Cisco	Adaptive Security Appliance Software	9.20.3.4	All	All	All
Operating System	Cisco	Adaptive Security Appliance Software	9.20.3.7	All	All	All
Operating System	Cisco	Adaptive Security Appliance Software	9.22.1.1	All	All	All
Hardware	Cisco	Secure Firewall 3105	-	All	All	All
Hardware	Cisco	Secure Firewall 3110	-	All	All	All
Hardware	Cisco	Secure Firewall 3120	-	All	All	All
Hardware	Cisco	Secure Firewall 3130	-	All	All	All
Hardware	Cisco	Secure Firewall 3140	-	All	All	All
Hardware	Cisco	Secure Firewall 4215	-	All	All	All
Hardware	Cisco	Secure Firewall 4225	-	All	All	All
Hardware	Cisco	Secure Firewall 4245	-	All	All	All
Application	Cisco	Secure Firewall Threat Defense	7.4.0	All	All	All
Application	Cisco	Secure Firewall Threat Defense	7.4.1	All	All	All
Application	Cisco	Secure Firewall Threat Defense	7.4.1.1	All	All	All
Application	Cisco	Secure Firewall Threat Defense	7.4.2	All	All	All
Application	Cisco	Secure Firewall Threat Defense	7.4.2.1	All	All	All
Application	Cisco	Secure Firewall Threat Defense	7.6.0	All	All	All

Vendor Declared Affected Products

Source	Vendor	Product	Version	Platforms
CNA	Cisco	Cisco Adaptive Security Appliance ASA Software	affected 9.20.1	Not specified
CNA	Cisco	Cisco Adaptive Security Appliance ASA Software	affected 9.20.1.5	Not specified
CNA	Cisco	Cisco Adaptive Security Appliance ASA Software	affected 9.20.2	Not specified
CNA	Cisco	Cisco Adaptive Security Appliance ASA Software	affected 9.20.2.10	Not specified
CNA	Cisco	Cisco Adaptive Security Appliance ASA Software	affected 9.20.2.21	Not specified
CNA	Cisco	Cisco Adaptive Security Appliance ASA Software	affected 9.20.2.22	Not specified
CNA	Cisco	Cisco Adaptive Security Appliance ASA Software	affected 9.20.3	Not specified
CNA	Cisco	Cisco Adaptive Security Appliance ASA Software	affected 9.22.1.1	Not specified
CNA	Cisco	Cisco Adaptive Security Appliance ASA Software	affected 9.20.3.4	Not specified
CNA	Cisco	Cisco Adaptive Security Appliance ASA Software	affected 9.20.3.7	Not specified
CNA	Cisco	Cisco Firepower Threat Defense Software	affected 7.4.0	Not specified
CNA	Cisco	Cisco Firepower Threat Defense Software	affected 7.4.1	Not specified
CNA	Cisco	Cisco Firepower Threat Defense Software	affected 7.4.1.1	Not specified
CNA	Cisco	Cisco Firepower Threat Defense Software	affected 7.4.2	Not specified
CNA	Cisco	Cisco Firepower Threat Defense Software	affected 7.6.0	Not specified
CNA	Cisco	Cisco Firepower Threat Defense Software	affected 7.4.2.1	Not specified

References

Reference	Source	Link	Tags
sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-3100_4...	[email protected]	sec.cloudapps.cisco.com	Vendor Advisory
CVE Program record	CVE.ORG	www.cve.org	canonical
NVD vulnerability detail	NVD	nvd.nist.gov	canonical, analysis

No vendor comments have been submitted for this CVE.

Additional Advisory Data

Exploits

CNA: The Cisco Product Security Incident Response Team (PSIRT) is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.

There are currently no legacy QID mappings associated with this CVE.