CVE-2021-1501

What it is

A vulnerability in the SIP inspection engine of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a crash and reload of an affected device, resulting in a denial of service (DoS) condition.The vulnerability is due to a crash that occurs during a hash lookup for a SIP pinhole connection. An attacker could exploit this vulnerability by sending crafted SIP traffic through an affected device. A successful exploit could allow the attacker to cause a crash and reload of the affected device.

At a glance

Exploitability

Can be exploited over the network without logging in. High risk of service disruption.

Exploit odds

1.4% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2021-04-29 18:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-08-11 19:33 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 1.4% in the next 30 days (EPSS).
• Severity: 8.6 HIGH (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2021-04-29 18:15 UTC

Last modified

2026-08-11 19:33 UTC

Exploit probability

1.4% · EPSS, next 30 days

Weakness

CWE-613

Record status

Modified

Affected

• Cisco Secure Firewall Threat Defense < 6.4.0.12
• Cisco Secure Firewall Threat Defense < 6.6.4
• Cisco Secure Firewall Threat Defense < 6.7.0.2
• Cisco Adaptive Security Appliance Software < 9.8.4.34
• Cisco Adaptive Security Appliance Software < 9.9.2.85
• Cisco Adaptive Security Appliance Software < 9.12.4.18
• Cisco Adaptive Security Appliance Software < 9.13.1.21
• Cisco Adaptive Security Appliance Software < 9.14.2.13

Attack profile CVSS 3.1 · 8.6

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Changed

Confidentiality

None

Integrity

None

Availability

High

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2021-1501.md and follow it. Check whether this project is affected by CVE-2021-1501. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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