CVE-2021-1573Network attack vector

Unauthenticated device reload via malformed HTTPS request

Published Jan 11, 2022 · Updated Nov 6, 2024

Improper input validation in Cisco ASA and FTD web services allows remote attackers to reload affected devices via malicious HTTPS requests. The web services HTTPS-request parser accepts malformed input without adequate validation and reaches a failure that restarts the appliance. Exposure requires a vulnerable release with AnyConnect IKEv2 client services, AnyConnect SSL VPN, or Clientless SSL VPN enabled; the reload interrupts firewall and VPN service.

CVSS severity8.6
High
EPSS probability1.31%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in Cisco ASA and FTD web services allows remote attackers to reload affected devices via malicious HTTPS requests. The web services HTTPS-request parser accepts malformed input without adequate validation and reaches a failure that restarts the appliance. Exposure requires a vulnerable release with AnyConnect IKEv2 client services, AnyConnect SSL VPN, or Clientless SSL VPN enabled; the reload interrupts firewall and VPN service.

The record

CVE
CVE-2021-1573
Published
Jan 11, 2022
Updated
Nov 6, 2024
Vendor
ClamAV
Product
Cisco Adaptive Security Appliance (ASA) Software
Classifications
CWE-787, CWE-121, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 11, 2022CVE publishedPublication date reported by the CVE source.
  2. Nov 6, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <6.4.0.13

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

ClamAV · Cisco Adaptive Security Appliance (ASA) Softwareversion=unspecified <6.4.0.13
ClamAV · Cisco Firepower Threat Defense Softwareversion=unspecified <6.6.5

Published CVSS scores

7.1NIST NVDAV:N/AC:M/Au:N/C:N/I:N/A:C
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
8.6Cisco Systems, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-787Out-of-bounds Write
CWE-121Stack-based Buffer Overflow
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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