Security readout for executives and security teams
Plain-English summary
This flaw can let an unauthenticated remote attacker crash and reload affected Cisco ASA or FTD security devices by sending a malformed SSL/TLS message when software-based SSL/TLS decryption is in use. The business impact is service interruption, not data theft or privilege gain, but affected perimeter devices can be critical path infrastructure.
Executive priority
Treat this as high priority for perimeter or remote-access security infrastructure. It is availability-focused, but a reload of firewall or threat-defense systems can interrupt connectivity, VPN access, or protected services.
Technical view
CVE-2021-34783 is an insufficient-validation flaw in Cisco ASA and FTD software-based SSL/TLS message handling. The CVSS 3.1 score is 8.6, with network attack vector, low complexity, no privileges, no user interaction, and high availability impact. Cisco notes DTLS messages cannot exploit it.
Likely exposure
Exposure is most likely where Cisco ASA or FTD devices process SSL/TLS traffic using software-based SSL/TLS decryption. The source bundle does not provide affected release ranges, so version exposure must be confirmed against Cisco guidance.
Exploitation context
The described attack is remote and unauthenticated, causing device reload and denial of service through crafted SSL/TLS input. The bundle does not cite CISA KEV listing or other evidence of active exploitation.
Researcher notes
Root cause is insufficient SSL/TLS message validation during software-based decryption, mapped to CWE-119 in the bundle. Impact is availability only. Evidence is incomplete on exact vulnerable versions and fix levels; rely on Cisco’s advisory for release-specific decisions.
Mitigation direction
- Review Cisco advisory for affected releases and fixed software guidance.
- Prioritize internet-facing or business-critical ASA and FTD deployments.
- Confirm whether software-based SSL/TLS decryption is enabled on relevant devices.
- Apply vendor-recommended updates or mitigations once confirmed.
- Monitor for unexpected reloads affecting ASA or FTD services.
Validation and detection
- Inventory Cisco ASA and FTD devices and their software versions.
- Check configurations for software-based SSL/TLS decryption use.
- Compare deployed versions against Cisco advisory applicability.
- Review device logs and uptime records for unexplained reloads.
- Confirm DTLS-only traffic is not treated as exploitable evidence.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-119: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2021-34783 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 8.6 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H3.94Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
8.6HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
Source materials
- CVE List V5 sourceCVE List V5
- 20211027 Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software Software-Based SSL/TLS Denial of Service VulnerabilityCVE reference · vendor-advisory, x_refsource_CISCO
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Restriction of Operations within the Bounds of a Memory Buffer
Improper Restriction of Operations within the Bounds of a Memory Buffer represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.