dbcve.org
AsyncosOperating system · Cisco

CVE-2023-20057

MEDIUM · 5.3 CVSS v3.1 Published 2023-01-20
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
62/100
Remediation priority · Elevated
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
A vulnerability in the URL filtering mechanism of Cisco AsyncOS Software for Cisco Email Security Appliance (ESA) could allow an unauthenticated, remote attacker to bypass the URL reputation filters on an affected device. This vulnerability is due to improper processing of URLs. An attacker could exploit this vulnerability by crafting a URL in a particular way. A successful exploit could allow the attacker to bypass the URL reputation filters that are configured for an affected device, which could allow malicious URLs to pass through the device.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · moderate confidence

Cisco AsyncOS Software for the Email Security Appliance contains a flaw in its URL filtering mechanism that allows specially crafted URLs to bypass reputation filters. An unauthenticated remote attacker can exploit this by manipulating URL structures to evade detection, potentially delivering malicious links through the ESA without triggering configured security controls.

MitigationApply the vendor patch from Cisco and verify URL filtering policies are functioning correctly after the update.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
AsyncosOperating system
Affected:all versions

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Confirm Cisco ESA appliance is present
    Identify if your environment includes a Cisco Email Security Appliance (ESA) device. Check network inventory, device documentation, or physically locate the appliance. This vulnerability affects only ESA devices running AsyncOS, not other Cisco products.
    Affected if You have a Cisco ESA appliance in your environment
  2. Determine AsyncOS version
    Access the ESA CLI or web interface and retrieve the AsyncOS version. In the CLI, this is typically shown on login or via the 'version' command. Compare your installed version against Cisco's patched releases for CVE-2023-20057.
    Affected if Your AsyncOS version is any release prior to Cisco's patched version for this CVE (the summary indicates all versions are affected)
  3. Verify URL filtering is enabled
    Access the ESA web interface or CLI and check the URL filtering configuration. Look for URL reputation filters, URL filtering policies, or the URL Filtering feature under your incoming/outgoing mail policies. Confirm whether this security control is actively applied to mail traffic.
    Affected if URL filtering policies are configured and active on your ESA
  4. Inspect mail logs for suspicious bypassed URLs
    Review ESA mail logs (via the GUI Log Subscriptions or CLI 'logs' command) for incoming emails around the time of potential exploitation. Look for URLs that may have unusual structures, unexpected characters, or patterns designed to evade reputation filters. Search for alerts related to URL filtering or blocked threats.
    Affected if Logs show URLs with unusual structures that may have bypassed your configured URL reputation filters

You are affected if you operate a Cisco ESA with any unpatched AsyncOS version and have URL filtering enabled, as the vulnerability allows malicious URLs to bypass your configured reputation filters.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply the vendor patch from Cisco and verify URL filtering policies are functioning correctly after the update.

Fix this in Asyncos Scoped from the published advisory
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,130
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Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2023-20057 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data