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Vulnerability record · CVE-2021-34783 · published 27 October 2021

CVE-2021-34783: Cisco secure firewall threat defense memory buffer overflow vulnerability

Cisco · Secure Firewall Threat Defense

A vulnerability in the software-based SSL/TLS message handler of Cisco Adaptive Security Appliance (ASA) Software and Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause an affected device to reload, resulting in a denial of service (DoS) condition. This vulnerability is due to insufficient validation of SSL/TLS messages when the device performs software-based SSL/TLS decryption. An attacker could exploit this vulnerability by sending a crafted SSL/TLS message to an affected device. A successful exploit could allow the attacker to cause the affected device to reload, resulting in a DoS condition. Note: Datagram TLS (DTLS) messages cannot be used to exploit this vulnerability.

7.5 CVSS 3.1 High EPSS 1.6% · top 25.2% CWE-119 · Memory buffer overflowCWE-20 · Improper input validation
7.5CVSS 3.1 base score, v2 7.8
1.6%EPSS exploitation probability, 30 days
NoNot in CISA KEV
10Affected product versions listed by NVD
2References
11 Aug 2026Last modified by NVD

Description

A vulnerability in the software-based SSL/TLS message handler of Cisco Adaptive Security Appliance (ASA) Software and Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause an affected device to reload, resulting in a denial of service (DoS) condition. This vulnerability is due to insufficient validation of SSL/TLS messages when the device performs software-based SSL/TLS decryption. An attacker could exploit this vulnerability by sending a crafted SSL/TLS message to an affected device. A successful exploit could allow the attacker to cause the affected device to reload, resulting in a DoS condition. Note: Datagram TLS (DTLS) messages cannot be used to exploit this vulnerability.

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

Affected products

10 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ftd-tls-decrypt-dos-BMxYjm8M Vendor Advisory
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ftd-tls-decrypt-dos-BMxYjm8M Vendor Advisory

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Source: NIST National Vulnerability Database (record CVE-2021-34783), CISA KEV, FIRST EPSS (scores of 2026-09-28). This page is refreshed as NVD updates the record.