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Findings

Vulnerability · CVE-2021-36580

icewarp icewarp_server URL Redirection to Untrusted Site ('Open Redirect')

Published Oct 1, 2026 · corrected/updated Oct 1, 2026 · icewarp icewarp_server · evidence confidence very high

Open Redirect vulnerability exists in IceWarp MailServer IceWarp Server Deep Castle 2 Update 1 (13.0.1.2) via the referer parameter.

Grounded briefings

Catalog interpretations for three audiences. Each brief cites ingested metadata and the original advisories below. They are not independent research and they do not invent exploit steps.

Executive

CVE-2021-36580 is a unknown public vulnerability record for icewarp icewarp_server. CISA lists it as known exploited. Published remediation guidance: Apply remediations or mitigations per vendor instructions or discontinue use of the product if remediation or mitigations are unavailable. This summary is a catalog interpretation of the ingested metadata and cites the original advisories below.

System administrator

Identify whether icewarp icewarp_server is in your estate, then compare installed versions with the affected ranges. Affected packages or ranges on record: icewarp icewarp_server. Published remediation guidance: Apply remediations or mitigations per vendor instructions or discontinue use of the product if remediation or mitigations are unavailable. Prefer the vendor or distribution advisory linked in Sources before changing production systems. This is a catalog interpretation, not a runbook.

Security analyst

Signals on file: EPSS 1.6%. CISA lists it as known exploited. Sources contributing to this record: cve_org, epss, vulncheck_kev. Public exploit references, when present, are outbound links only and are not proof of active exploitation. This is a catalog interpretation of stored metadata.

Exploitation and remediation

  • Exploitation evidence

    Confirmed in CISA KEV since Oct 1, 2026. Listed in CISA KEV and VulnCheck KEV.

  • Patch and remediation

    Apply remediations or mitigations per vendor instructions or discontinue use of the product if remediation or mitigations are unavailable.

  • Safe detection guidance

    Compare installed versions with the affected ranges below and verify the advisory from the original publisher. This site stores metadata and outbound links only; it does not ship exploit code or proof-of-concept payloads.

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Oct 1, 2026 · VulnCheck KEV

    Detected

    Open Redirect vulnerability exists in IceWarp MailServer IceWarp Server Deep Castle 2 Update 1 (13.0.1.2) via the referer parameter.

  2. Oct 1, 2026 · CISA KEV

    Known exploited

    Apply remediations or mitigations per vendor instructions or discontinue use of the product if remediation or mitigations are unavailable.

Affected

  • vendor icewarp icewarp_serverversion unspecified

Sources

  • CVE.orgVulnerability recordCVE-2021-36580

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2021-36580

    30-day exploitation probability 1.6%

    first.org
  • VulnCheck KEVConfirmed exploitationCVE-2021-36580

    Open Redirect vulnerability exists in IceWarp MailServer IceWarp Server Deep Castle 2 Update 1 (13.0.1.2) via the referer parameter.

    vulncheck.com

References