# What is CVE-2021-1402?

> CVE-2021-1402 is a high-severity flaw (CVSS 8.6) in Firepower Threat Defense from Cisco, published on 29 April 2021. It is not on the list of flaws known to be exploited today. The latest forecast puts its chance of use in the next 30 days at 1.4%. If you run an affected version, plan in the vendor’s fix.

Canonical page: https://www.precursorintelligence.com/what-is/cve-2021-1402

## At a glance

- **Verdict:** Plan it in. No sign of exploitation and a low forecast. Patch it in your normal update cycle.
- **Precursor Intelligence risk score:** 47 out of 100 (Medium); action: Plan remediation. Kept up to date as the evidence changes.
- **Severity:** High (CVSS 8.6 out of 10)
- **Known to be exploited:** No, not on the list of flaws known to be exploited today
- **Chance of use in the next 30 days:** 1.4% (latest exploit-likelihood forecast)
- **Published:** 29 April 2021
- **Record last updated:** 5 August 2022
- **Main product:** Firepower Threat Defense from Cisco
- **Affected products:** 16

## What is CVE-2021-1402? In plain terms

It can be attacked from anywhere on the internet without logging in, and nobody has to click anything. If it works, the attacker can take it offline.

### The official description

A vulnerability in the software-based SSL/TLS message handler of Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to trigger a reload of an affected device, resulting in a denial of service (DoS) condition. The vulnerability is due to insufficient validation of SSL/TLS messages when the device performs software-based SSL decryption. An attacker could exploit this vulnerability by sending a crafted SSL/TLS message through an affected device. SSL/TLS messages sent to an affected device do not trigger this vulnerability. A successful exploit could allow the attacker to cause a process to crash. This crash would then trigger a reload of the device. No manual intervention is needed to recover the device after the reload.

### What kind of flaw is it?

- CWE-20: Improper Input Validation
- CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer

### How an attack on it works

- Where an attacker can be: Anywhere on the internet
- How hard it is to pull off: Easy: no special conditions
- Login needed first: No login needed
- Does someone have to click: No, nobody has to do anything
- What an attacker gets: Can take it offline

Severity vector: `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H`

## Is CVE-2021-1402 being exploited? Not that we know of

It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 1.4%. That can change at any time, which is why we keep watching.

Exploit likelihood over the last 7 days: 1.4%, 1.4%, 1.4%, 1.4%, 1.4%, 1.4%, 1.4%.

### Timeline

- 29 April 2021: Published
- 5 August 2022: Record last updated

### How Precursor Intelligence ranks it

CVE-2021-1402 scores **47 out of 100 (Medium)**, with the action "Plan remediation".

Every published flaw gets a risk score from 0 to 100, kept up to date as the evidence changes. Four things go into the score, from the one that counts most to the ones that count less:

- Evidence it is being exploited: biggest factor
- How severe it is: strong factor
- How widely exposed it is: smaller factor
- Threat activity around it: smaller factor

85 and above is Critical. Anything confirmed as exploited is always marked for an emergency patch, whatever its score. When this flaw matches software you track, it lands in your list with its score and the reasons behind it.

## Who is affected by CVE-2021-1402?

The published record lists 16 products. Versions are as published: "6.3.0 to before 6.4.0" means from 6.3.0 up to, but not including, 6.4.0.

- [Firepower Threat Defense](https://www.precursorintelligence.com/product/cisco/firepower_threat_defense) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Application): 6.3.0 to before 6.4.0, 6.5.0 to before 6.6.0
- [ASA 5512-X](https://www.precursorintelligence.com/product/cisco/asa_5512-x) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): version not specified
- [ASA 5515-X](https://www.precursorintelligence.com/product/cisco/asa_5515-x) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): version not specified
- [ASA 5525-X](https://www.precursorintelligence.com/product/cisco/asa_5525-x) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): version not specified
- [ASA 5545-X](https://www.precursorintelligence.com/product/cisco/asa_5545-x) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): version not specified
- [ASA 5555-X](https://www.precursorintelligence.com/product/cisco/asa_5555-x) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): version not specified
- [Firepower 1010](https://www.precursorintelligence.com/product/cisco/firepower_1010) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): version not specified
- [Firepower 1120](https://www.precursorintelligence.com/product/cisco/firepower_1120) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): version not specified
- [Firepower 1140](https://www.precursorintelligence.com/product/cisco/firepower_1140) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): version not specified
- [Firepower 1150](https://www.precursorintelligence.com/product/cisco/firepower_1150) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): version not specified
- [Firepower 2110](https://www.precursorintelligence.com/product/cisco/firepower_2110) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): version not specified
- [Firepower 2120](https://www.precursorintelligence.com/product/cisco/firepower_2120) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): version not specified
- [Firepower 2130](https://www.precursorintelligence.com/product/cisco/firepower_2130) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): version not specified
- [Firepower 2140](https://www.precursorintelligence.com/product/cisco/firepower_2140) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): version not specified
- [Firepower Threat Defense Virtual](https://www.precursorintelligence.com/product/cisco/firepower_threat_defense_virtual) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Application): version not specified
- [Isa 3000](https://www.precursorintelligence.com/product/cisco/isa_3000) by [Cisco](https://www.precursorintelligence.com/vendors/cisco) (Hardware): version not specified

## How do I fix CVE-2021-1402?

1. **Check whether you run it.** Compare your versions with the affected products above. Not sure what you run? Precursor Intelligence can work it out from your public website, or you can pick it from a list.
2. **Apply the vendor’s fix.** Install the update named in the vendor’s advisory. We’ve put the advisory first in the list.
3. **If you can’t patch today.** Follow any mitigation the vendor publishes, and limit who can reach the affected system from the internet until the update is in.
4. **Keep an eye on it.** Track the product and we tell you as soon as we spot this flaw on the list of exploited flaws, or a jump in its exploit likelihood.

### References

- [tools.cisco.com](https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ftd-ssl-decrypt-dos-DdyLuK6c) (Vendor advisory)

## Questions

### What is CVE-2021-1402?

CVE-2021-1402 is a high-severity flaw in Firepower Threat Defense from Cisco, published on 29 April 2021. It can be attacked from anywhere on the internet without logging in, and nobody has to click anything. If it works, the attacker can take it offline.

### How serious is CVE-2021-1402?

It scores 8.6 out of 10 on the CVSS severity scale, which is high. Our risk score for CVE-2021-1402 is 47 out of 100, which is Medium. Its action is "Plan remediation". No sign of exploitation and a low forecast. Patch it in your normal update cycle.

### Is CVE-2021-1402 being exploited?

It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 1.4%. That can change at any time, which is why we keep watching.

### Which versions does CVE-2021-1402 affect?

For Firepower Threat Defense from Cisco: 6.3.0 to before 6.4.0, 6.5.0 to before 6.6.0. The record lists 16 products in all, each with its versions, under "Who is affected" on this page.

### How do I fix CVE-2021-1402?

Install the update the vendor names in its advisory, linked first under "How do I fix" on this page. If you can't patch today, follow the vendor's mitigation and limit who can reach the affected system from the internet.

## Does CVE-2021-1402 affect you?

Precursor Intelligence keeps checking for you:

- **Tell us what you run.** Pick your software from a list, or let us work it out from your website.
- **We match it to every flaw.** Over 400,000 published flaws, checked against your list.
- **Ranked by real-world risk.** Every flaw gets a 0 to 100 risk score, kept up to date, led by evidence criminals are using it.
- **Told as soon as we know.** An alert by email, in the app or by webhook to your own tools.

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