CVE-2025-20127Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software for Firepower 3100 and 4200 Series TLS Cipher Denial of Service Vulnerability
- 7.7HighCVSS base score
- 0.69%Exploitation in 30 daysEPSS · top 47% of all CVEs
- NoKnown exploitednot in CISA's KEV catalog
- NonePublic exploitsnone known yet
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.
Timeline
ID reserved
By cisco
- 10 months later
· 10 months later
Published
- 20 days later
· 20 days later
Record updated
Changes after publication (a new score, a public exploit, EPSS crossing 1, 10 or 50 %, leaving KEV) are kept since November 2026; earlier ones are not known.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| ciscoCNA (assigner) | 3.1 | High7.7 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H |
| NVDNVD · Analyzed | 3.1 | High7.7 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:N/I:N/A:H |
- EPSS (exploitation in 30 days)
- 0.69% · top 47% of all CVEs (14 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: no · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.7.
Affected products
Cisco · Cisco Adaptive Security Appliance (ASA) Software
- affected 9.20.1
- affected 9.20.1.5
- affected 9.20.2
- affected 9.20.2.10
- affected 9.20.2.21
- affected 9.20.2.22
- affected 9.20.3
- affected 9.22.1.1
- affected 9.20.3.4
- affected 9.20.3.7
Cisco · Cisco Firepower Threat Defense Software
- affected 7.4.0
- affected 7.4.1
- affected 7.4.1.1
- affected 7.4.2
- affected 7.6.0
- affected 7.4.2.1
What to do
Exploitation: 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.
References
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- EUVD EUVD-2025-24854 (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://cveledger.app/cve/CVE-2025-20127)Record last updated .