# CVE-2026-20135

TLS 1.3 parsing bug in Cisco FTD allows crafted packets to crash device (DoS).

- Page: https://www.vulneraibility.com/cve/CVE-2026-20135
- CVSS: 8.6
- Known exploited: not in CISA KEV as of our last sync
- EPSS: 0.67% (percentile 51.9)
- CISA SSVC: exploitation none, automatable yes, technical impact partial (assessed 2026-09-17)
- Weakness: CWE-415
- Published: 2026-09-16

## Affected versions

- Cisco Cisco Secure Firewall Threat Defense (FTD) Software: affected 7.0.0; 7.0.0.1; 7.0.1; 7.0.1.1; 7.0.2; 7.2.0; 7.0.2.1; 7.0.3; 7.2.0.1; 7.0.4; 7.2.1; 7.0.5; 7.3.0; 7.2.2; 7.2.3; 7.3.1; 7.2.4; 7.0.6; 7.2.5; 7.2.4.1; 7.3.1.1; 7.4.0; 7.0.6.1; 7.2.5.1; 7.4.1; 7.2.6; 7.0.6.2; 7.4.1.1; 7.2.7; 7.2.5.2; 7.3.1.2; 7.2.8; 7.6.0; 7.4.2; 7.2.8.1; 7.0.6.3; 7.4.2.1; 7.2.9; 7.0.7; 7.7.0; 7.4.2.2; 7.2.10; 7.6.1; 7.4.2.3; 7.0.8; 7.6.2; 7.7.10; 7.7.11; 7.0.8.1; 7.6.2.1; 7.7.10.1; 7.4.2.4; 7.2.10.2; 7.4.3; 7.6.4; 7.4.4; 7.0.9; 7.2.11

A version outside these ranges is not a statement that it is unaffected.

## Impact

Remote unauthenticated attacker can send a crafted TLS1.3 packet to crash the LINA process and force device reload, causing network/firewall DoS.

## Action

Patch when possible

## Recommendation

Apply vendor advisory guidance; update ASAP or restrict/expose TLS1.3 listeners.

## References

- [other] https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ftd-tls1.3-dos-dLxwFWgF

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Summary, impact and action are written by the vulneraibility.com AI analysis pipeline from the CVE record, NVD, CISA and FIRST data; verify against the references.