Asyncos
CVE-2021-34741
HIGH
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A06:2025 - Insecure Design
ASVS 5.0
V2 - Validation and Business Logic Resource allocation limits
MITRE ATT&CK
1 technique across 1 tactic: Impact The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. |
| Impact | CVSS score of 7.5 (HIGH). Attack characteristics: network attack vector, low complexity, no privileges required, no user interaction not required. |
| Exploit ScenarioDerived | A remote attacker could exhaust system resources through uncontrolled allocation by sending crafted requests to the affected application. No authentication is required to exploit this vulnerability. |
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Alert meAnalysisAI
A vulnerability in the email scanning algorithm of Cisco AsyncOS software for Cisco Email Security Appliance (ESA) could allow an unauthenticated, remote attacker to perform a denial of service (DoS). Rated high severity (CVSS 7.5), this vulnerability is remotely exploitable, no authentication required, low attack complexity. No vendor patch available.
RemediationAI
No vendor patch is available at time of analysis. Monitor vendor advisories for updates. Set resource limits, implement rate limiting, validate input sizes.
Affects your stack
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Checking this CVE against your own stacks and servers is part of the Basic plan and up.
Technical ContextAI · show details
This vulnerability is classified as Allocation of Resources Without Limits (CWE-770), which allows attackers to exhaust system resources through uncontrolled allocation. A vulnerability in the email scanning algorithm of Cisco AsyncOS software for Cisco Email Security Appliance (ESA) could allow an unauthenticated, remote attacker to perform a denial of service (DoS) attack against an affected device. This vulnerability is due to insufficient input validation of incoming emails. An attacker could exploit this vulnerability by sending a crafted email through Cisco ESA. A successful exploit could allow the attacker to exhaust all the available CPU resources on an affected device for an extended period of time, preventing other emails from being processed and resulting in a DoS condition. Affected products include: Cisco Asyncos.
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- Exploit and PoC references, threat intelligence from 22 sources
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Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Primary rating from NVD · only source for this CVE.
CVSS VectorNVD
DescriptionNVD
A vulnerability in the email scanning algorithm of Cisco AsyncOS software for Cisco Email Security Appliance (ESA) could allow an unauthenticated, remote attacker to perform a denial of service (DoS) attack against an affected device. This vulnerability is due to insufficient input validation of incoming emails. An attacker could exploit this vulnerability by sending a crafted email through Cisco ESA. A successful exploit could allow the attacker to exhaust all the available CPU resources on an affected device for an extended period of time, preventing other emails from being processed and resulting in a DoS condition.
Threat Intelligence Overview
NVD
CVE.org
EPSS
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Denial of Service attacks render applications or systems unavailable by overwhelming resources or triggering failure conditions.
Affected Products (CPE)NVD
A vulnerability in the web-based management interface of Cisco Email Security Appliance, Cisco Secure Email and Web Mana
A vulnerability in the configuration management of Cisco AsyncOS for Cisco Web Security Appliance (WSA) could allow an a
A vulnerability in the web management interface of Cisco AsyncOS Software for Cisco Web Security Appliance (WSA) could a
A vulnerability in the HTTPS decryption feature of Cisco Web Security Appliance (WSA) could allow an unauthenticated, re
A vulnerability in the web-based management interface of Cisco AsyncOS Software for Cisco Secure Email and Web Manager c
A vulnerability in the CLI of Cisco AsyncOS for Secure Web Appliance could allow an authenticated, local attacker to exe
A vulnerability in the log subscription subsystem of Cisco AsyncOS for the Cisco Secure Web Appliance (formerly Web Secu
A vulnerability in the administrative shell of Cisco AsyncOS on Cisco Email Security Appliance (ESA) and Content Securit
Cisco AsyncOS on Email Security Appliance (ESA) devices through 9.7.0-125 allows remote attackers to bypass malware dete
Cisco AsyncOS 9.7.0-125 on Email Security Appliance (ESA) devices allows remote attackers to bypass intended spam filter
A vulnerability in the DNS-based Authentication of Named Entities (DANE) email verification component of Cisco AsyncOS S
A vulnerability in the proxy service of Cisco AsyncOS for Cisco Web Security Appliance (WSA) could allow an unauthentica
GitHub PoC
Exploit-DB