Cyber Resilience

CVE-2024-20353

DoS in Cisco Adaptive Security Appliance Software 9.12.1 … 9.8.4.8

CISA KEVActive ExploitationEUVD ExploitedPublic PoCDoS
Published
24 April 2024
Modified
11 August 2026
KEV Added
24 April 2024
Patch / advisory
CVSS Score v3.1 8.6
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
EPSS Score 0.71 99.3th percentile
Risk Priority 88 floored blend · peak EPSS

Summary

CVE-2024-20353 is a high-severity Infinite Loop (CWE-835) vulnerability in Cisco Adaptive Security Appliance Software. Its CVSS base score is 8.6 (High).

Operationally, exploitation aligns with the MITRE ATT&CK technique Application or System Exploitation (T1499.004); ranked in the top 0.7% of CVEs by exploit likelihood; CISA has added it to the Known Exploited Vulnerabilities catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SI-2 (Flaw Remediation) — see the control section below for these in your framework.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

CVE-2024-20353 affects the management and VPN web servers in Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software. The flaw stems from incomplete error checking during HTTP header parsing and carries a CVSS 3.1 score of 8.6. Successful exploitation triggers an unexpected device reload and resulting denial-of-service condition.

An unauthenticated remote attacker can trigger the vulnerability by sending a single crafted HTTP request to either web server interface. No authentication or user interaction is required, and the attack can be launched over the network with low complexity, allowing an adversary to interrupt device operation and availability.

The Cisco Security Advisory and CISA Known Exploited Vulnerabilities catalog both list the issue, confirming that affected customers should apply the fixes published in the vendor advisory. The vulnerability has also been linked to the ArcaneDoor espionage campaign that targeted perimeter network devices.

EPSS scores rose from a low baseline to a recorded peak of 0.2445 (current value 0.1883), indicating emerging exploitation interest after public disclosure and warranting renewed attention from defenders.

EU & UK References

Vulnerability Data

A vulnerability in the management and VPN web servers for Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause the device to reload unexpectedly, resulting in a denial…

more

of service (DoS) condition. This vulnerability is due to incomplete error checking when parsing an HTTP header. An attacker could exploit this vulnerability by sending a crafted HTTP request to a targeted web server on a device. A successful exploit could allow the attacker to cause a DoS condition when the device reloads.

CWE(s)
KEV Date Added
24 April 2024

Related Threats

Threat-Actor AttributionAI

Arcanedoor (C0046)
Talos blog (referenced in CISA/CVE entries) attributes espionage campaign targeting Cisco ASA/FTD perimeter devices to Arcanedoor, exploiting this CVE-class flaw.

MITRE ATT&CK Enterprise Techniques

T1499.004 Application or System Exploitation Impact
Adversaries may exploit software vulnerabilities that can cause an application or system to crash and deny availability to users.
T1499 Endpoint Denial of Service Impact
Adversaries may perform Endpoint Denial of Service (DoS) attacks to degrade or block the availability of services to users.
T1499.003 Application Exhaustion Flood Impact
Adversaries may target resource intensive features of applications to cause a denial of service (DoS), denying availability to those applications.
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2024-20481Same product: Cisco Adaptive Security Appliance Softwareboth on KEV
CVE-2025-20333Same product: Cisco Adaptive Security Appliance Softwareboth on KEV
CVE-2020-3580Same product: Cisco Adaptive Security Appliance Softwareboth on KEV
CVE-2025-20362Same product: Cisco Adaptive Security Appliance Softwareboth on KEV
CVE-2020-3259Same product: Cisco Adaptive Security Appliance Softwareboth on KEV
CVE-2026-20349Same product: Cisco Adaptive Security Appliance Softwareboth on KEV
CVE-2023-20083Same product: Cisco Secure Firewall Threat Defense
CVE-2024-20359Same product: Cisco Adaptive Security Appliance Softwareboth on KEV
CVE-2023-20269Same product: Cisco Adaptive Security Appliance Softwareboth on KEV
CVE-2026-20014Same product: Cisco Adaptive Security Appliance Software

Affected Assets

cisco
adaptive security appliance software
9.12.1, 9.12.1.2, 9.12.1.3, 9.12.2, 9.12.2.1
cisco
secure firewall threat defense
6.2.3, 6.2.3.1, 6.2.3.10, 6.2.3.11, 6.2.3.12

Mitigating Controls

Mitigating Controls (NIST 800-53 r5) AI

Developer testing and evaluation can discover unreachable loop exit conditions through static analysis, fuzzing, or execution tracing.

Flaw remediation processes identify and correct infinite-loop defects reported from testing or operations.

Requiring documented development processes and secure coding standards reduces introduction of loops whose termination conditions are unreachable.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure SDLC practices (reviews, testing, static analysis) directly prevent introduction of infinite-loop defects.

ID.RA-01 partial match
prevents

Static analysis and vuln scanning during asset assessment can detect unreachable loop exits.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

finds

Security testing can uncover infinite-loop conditions before release.

prevents

Secure development life cycle mandates practices that can detect and prevent infinite-loop defects.

prevents

Application security requirements can specify loop-termination rules, indirectly reducing the weakness.

prevents

Secure coding standards directly address loop termination and prevent infinite loops.

none

Secure architecture principles encourage designs that avoid unreachable exit conditions.

none

Change management can require review of loop logic when code is modified.

References