Encrypted-connection denial of service via TLS handle exhaustion
Published Aug 14, 2025 · Updated Sep 3, 2025
Resource exhaustion in Cisco ASA and FTD Software on 3100/4200 devices allows remote authenticated users to block encrypted connections. Repeated TLS 1.3 connections using TLS_CHACHA20_POLY1305_SHA256 consume Security Context Block handles needed for incoming encryption. Affected devices require an SSL listen socket and the non-default cipher; once handles run out, they reject new SSL, TLS, VPN, and IKE connections until reloaded.
Summary
What happened
Resource exhaustion in Cisco ASA and FTD Software on 3100/4200 devices allows remote authenticated users to block encrypted connections. Repeated TLS 1.3 connections using TLS_CHACHA20_POLY1305_SHA256 consume Security Context Block handles needed for incoming encryption. Affected devices require an SSL listen socket and the non-default cipher; once handles run out, they reject new SSL, TLS, VPN, and IKE connections until reloaded.
The record
- CVE
- CVE-2025-20127
- Published
- Aug 14, 2025
- Updated
- Sep 3, 2025
- Vendor
- ClamAV
- Product
- Cisco Adaptive Security Appliance (ASA) Software
- Classifications
- CWE-404, T1499.002
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Aug 14, 2025CVE publishedPublication date reported by the CVE source.
- Sep 3, 2025Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=9.20.1
- Affected versionversion=9.20.1.5
- Affected versionversion=9.20.2
- Affected versionversion=9.20.2.10
- Affected versionversion=9.20.2.21
- Affected versionversion=9.20.2.22
- Affected versionversion=9.20.3
- Affected versionversion=9.20.3.4
- Affected versionversion=9.20.3.7
- Affected versionversion=9.22.1.1
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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