CVE-2021-1534Network attack vector

URL reputation filter bypass via crafted URLs

Published Oct 6, 2021 · Updated Nov 7, 2024

Improper URL processing in Cisco AsyncOS for Secure Email Gateway before 14.0.1 allows remote attackers to bypass URL reputation filters. The antispam URL-processing path accepts a specially crafted URL without applying the configured reputation-filter decision, but Cisco has not disclosed the parsing error. No authentication or user interaction is required, and successful exploitation lets malicious URLs traverse the gateway in email.

CVSS severity5.8
Medium
EPSS probability1.07%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper URL processing in Cisco AsyncOS for Secure Email Gateway before 14.0.1 allows remote attackers to bypass URL reputation filters. The antispam URL-processing path accepts a specially crafted URL without applying the configured reputation-filter decision, but Cisco has not disclosed the parsing error. No authentication or user interaction is required, and successful exploitation lets malicious URLs traverse the gateway in email.

The record

CVE
CVE-2021-1534
Published
Oct 6, 2021
Updated
Nov 7, 2024
Vendor
ClamAV
Product
Cisco Secure Email Gateway
Classifications
CWE-20, T1562
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 6, 2021CVE publishedPublication date reported by the CVE source.
  2. Nov 7, 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?

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  1. Affected versionversion=n/a

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

ClamAV · Cisco Secure Email Gatewayversion=n/a

Published CVSS scores

5.8CiscoCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N/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.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-20Improper Input Validation
T1562Impair Defenses

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

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Your stack

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