CVE-2021-26858 (GCVE-0-2021-26858)

Vulnerability from cvelistv5 – Published: 2021-03-02 23:55 – Updated: 2025-10-21 23:25
Title
Microsoft Exchange Server Remote Code Execution Vulnerability
Summary
Microsoft Exchange Server Remote Code Execution Vulnerability
SSVC
Exploitation: active Automatable: no Technical Impact: total
CISA Coordinator (v2.0.3)
CWE
Assigner
References
Impacted products
Vendor Product Version
Microsoft Microsoft Exchange Server 2019 Affected: 15.02.0 , < publication (custom)
    cpe:2.3:a:microsoft:exchange_server:2019:*:*:*:*:*:*:*
Create a notification for this product.
Microsoft Microsoft Exchange Server 2013 Cumulative Update 22 Affected: 15.00.0 , < publication (custom)
    cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_22:*:*:*:*:*:*
Create a notification for this product.
Microsoft Microsoft Exchange Server 2019 Cumulative Update 2 Affected: 15.02.0 , < publication (custom)
    cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_2:*:*:*:*:*:*
Create a notification for this product.
Microsoft Microsoft Exchange Server 2016 Cumulative Update 13 Affected: 15.01.0 , < publication (custom)
    cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_13:*:*:*:*:*:*
Create a notification for this product.
Microsoft Microsoft Exchange Server 2013 Cumulative Update 23 Affected: 15.00.0 , < publication (custom)
    cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_23:*:*:*:*:*:*
Create a notification for this product.
Microsoft Microsoft Exchange Server 2019 Cumulative Update 3 Affected: 15.02.0 , < publication (custom)
    cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_3:*:*:*:*:*:*
Create a notification for this product.
Microsoft Microsoft Exchange Server 2016 Cumulative Update 14 Affected: 15.01.0 , < publication (custom)
    cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_14:*:*:*:*:*:*
Create a notification for this product.
Microsoft Microsoft Exchange Server 2019 Cumulative Update 4 Affected: 15.02.0 , < publication (custom)
    cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_4:*:*:*:*:*:*
Create a notification for this product.
Microsoft Microsoft Exchange Server 2016 Cumulative Update 15 Affected: 15.01.0 , < publication (custom)
    cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_15:*:*:*:*:*:*
Create a notification for this product.
Microsoft Microsoft Exchange Server 2019 Cumulative Update 5 Affected: 15.02.0 , < publication (custom)
    cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_5:*:*:*:*:*:*
Create a notification for this product.
Microsoft Microsoft Exchange Server 2019 Cumulative Update 6 Affected: 15.02.0 , < publication (custom)
    cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_6:*:*:*:*:*:*
Create a notification for this product.
Microsoft Microsoft Exchange Server 2016 Cumulative Update 16 Affected: 15.01.0 , < publication (custom)
    cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_16:*:*:*:*:*:*
Create a notification for this product.
Microsoft Microsoft Exchange Server 2016 Cumulative Update 17 Affected: 15.01.0 , < publication (custom)
    cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_17:*:*:*:*:*:*
Create a notification for this product.
Microsoft Microsoft Exchange Server 2019 Cumulative Update 7 Affected: 15.02.0 , < publication (custom)
    cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_7:*:*:*:*:*:*
Create a notification for this product.
Microsoft Microsoft Exchange Server 2016 Cumulative Update 18 Affected: 15.01.0 , < publication (custom)
    cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_18:*:*:*:*:*:*
Create a notification for this product.
Microsoft Microsoft Exchange Server 2016 Cumulative Update 19 Affected: 15.01.0 , < publication (custom)
    cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_19:*:*:*:*:*:*
Create a notification for this product.
Microsoft Microsoft Exchange Server 2019 Cumulative Update 8 Affected: 15.02.0 , < publication (custom)
    cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_8:*:*:*:*:*:*
Create a notification for this product.
Microsoft Microsoft Exchange Server 2013 Cumulative Update 21 Affected: 15.00.0 , < publication (custom)
    cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_21:*:*:*:*:*:*
Create a notification for this product.
Microsoft Microsoft Exchange Server 2016 Cumulative Update 12 Affected: 15.01.0 , < publication (custom)
    cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_12:*:*:*:*:*:*
Create a notification for this product.
Microsoft Microsoft Exchange Server 2016 Cumulative Update 8 Affected: 15.01.0 , < publication (custom)
    cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_8:*:*:*:*:*:*
Create a notification for this product.
Microsoft Microsoft Exchange Server 2019 Cumulative Update 1 Affected: 15.02.0 , < publication (custom)
    cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_1:*:*:*:*:*:*
Create a notification for this product.
Microsoft Microsoft Exchange Server 2016 Cumulative Update 9 Affected: 15.01.0 , < publication (custom)
    cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_9:*:*:*:*:*:*
Create a notification for this product.
Microsoft Microsoft Exchange Server 2016 Cumulative Update 10 Affected: 15.01.0 , < publication (custom)
    cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_10:*:*:*:*:*:*
Create a notification for this product.
Microsoft Microsoft Exchange Server 2016 Cumulative Update 11 Affected: 15.01.0 , < publication (custom)
    cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_11:*:*:*:*:*:*
Create a notification for this product.
Date Public
2021-03-02 08:00
CISA KEV
Known Exploited Vulnerability - GCVE BCP-07 Compliant

Vulnerability ID: CVE-2021-26858

Status: Confirmed

Status Updated: 2021-11-03 00:00 UTC

Exploited: Yes


Timestamps
First Seen: 2021-11-03
Asserted: 2021-11-03

Scope
Notes: KEV entry: Microsoft Exchange Server Remote Code Execution Vulnerability | Affected: Microsoft / Exchange Server | Description: Microsoft Exchange Server contains an unspecified vulnerability that allows for remote code execution. This vulnerability is part of the ProxyLogon exploit chain. | Required action: Apply updates per vendor instructions. | Due date: 2022-05-03 | Known ransomware campaign use (KEV): Known | Notes (KEV): Reference CISA's ED 21-02 (https://www.cisa.gov/news-events/directives/ed-21-02-mitigate-microsoft-exchange-premises-product-vulnerabilities) for further guidance and requirements. Note: The due date for addressing this vulnerability aligns with the requirements outlined in ED 21-02. https://nvd.nist.gov/vuln/detail/CVE-2021-26858

Evidence

Type: Vendor Report

Signal: Successful Exploitation

Confidence: 80%

Source: cisa-kev


Details
Cwes
Feed CISA Known Exploited Vulnerabilities Catalog
Product Exchange Server
Due Date 2022-05-03
Date Added 2021-11-03
Vendorproject Microsoft
Vulnerabilityname Microsoft Exchange Server Remote Code Execution Vulnerability
Knownransomwarecampaignuse Known

References

Created: 2026-02-02 12:28 UTC | Updated: 2026-02-06 07:17 UTC
KEVintel KEV
Known Exploited Vulnerability - GCVE BCP-07 Compliant

Vulnerability ID: CVE-2021-26858

Status: Confirmed

Status Updated: 2021-11-03 00:00 UTC

Exploited: Yes


Timestamps
First Seen: 2021-11-03
Asserted: 2021-11-03

Scope
Notes: KEVIntel entry: Microsoft Exchange Server Remote Code Execution Vulnerability | Affected: Microsoft / Microsoft Exchange Server 2019, Microsoft Exchange Server 2013 Cumulative Update 22, Microsoft Exchange Server 2019 Cumulative Update 2, Microsoft Exchange Server 2016 Cumulative Update 13, Microsoft Exchange Server 2013 Cumulative Update 23, Microsoft Exchange Server 2019 Cumulative Update 3, Microsoft Exchange Server 2016 Cumulative Update 14, Microsoft Exchange Server 2019 Cumulative Update 4, Microsoft Exchange Server 2016 Cumulative Update 15, Microsoft Exchange Server 2019 Cumulative Update 5, Microsoft Exchange Server 2019 Cumulative Update 6, Microsoft Exchange Server 2016 Cumulative Update 16, Microsoft Exchange Server 2016 Cumulative Update 17, Microsoft Exchange Server 2019 Cumulative Update 7, Microsoft Exchange Server 2016 Cumulative Update 18, Microsoft Exchange Server 2016 Cumulative Update 19, Microsoft Exchange Server 2019 Cumulative Update 8, Microsoft Exchange Server 2013 Cumulative Update 21, Microsoft Exchange Server 2016 Cumulative Update 12, Microsoft Exchange Server 2016 Cumulative Update 8, Microsoft Exchange Server 2019 Cumulative Update 1, Microsoft Exchange Server 2016 Cumulative Update 9, Microsoft Exchange Server 2016 Cumulative Update 10, Microsoft Exchange Server 2016 Cumulative Update 11 | CVSS: 7.8 (HIGH) | EPSS: 0.89509 | Used in malware: yes | Not yet in CISA KEV: False

Evidence

Type: Public Report

Signal: Confirmed Compromise

Confidence: 70%

Source: kevintel


Details
Feed KEVIntel (kevintel.com)
Title Microsoft Exchange Server Remote Code Execution Vulnerability
Vendor Microsoft
Product Microsoft Exchange Server 2019, Microsoft Exchange Server 2013 Cumulative Update 22, Microsoft Exchange Server 2019 Cumulative Update 2, Microsoft Exchange Server 2016 Cumulative Update 13, Microsoft Exchange Server 2013 Cumulative Update 23, Microsoft Exchange Server 2019 Cumulative Update 3, Microsoft Exchange Server 2016 Cumulative Update 14, Microsoft Exchange Server 2019 Cumulative Update 4, Microsoft Exchange Server 2016 Cumulative Update 15, Microsoft Exchange Server 2019 Cumulative Update 5, Microsoft Exchange Server 2019 Cumulative Update 6, Microsoft Exchange Server 2016 Cumulative Update 16, Microsoft Exchange Server 2016 Cumulative Update 17, Microsoft Exchange Server 2019 Cumulative Update 7, Microsoft Exchange Server 2016 Cumulative Update 18, Microsoft Exchange Server 2016 Cumulative Update 19, Microsoft Exchange Server 2019 Cumulative Update 8, Microsoft Exchange Server 2013 Cumulative Update 21, Microsoft Exchange Server 2016 Cumulative Update 12, Microsoft Exchange Server 2016 Cumulative Update 8, Microsoft Exchange Server 2019 Cumulative Update 1, Microsoft Exchange Server 2016 Cumulative Update 9, Microsoft Exchange Server 2016 Cumulative Update 10, Microsoft Exchange Server 2016 Cumulative Update 11
Added Date 2021-11-03T00:00:00.000Z
Cvss Score 7.8
Epss Score 0.89509
Cvss Severity HIGH
Epss Percentile 0.99769
Used In Malware yes
Ahead Of Cisa Kev None
Not Yet In Cisa Kev False

References

Created: 2026-06-19 12:48 UTC | Updated: 2026-06-19 12:48 UTC
Show details on NVD website

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          "url": "https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26858"
        }
      ],
      "title": "Microsoft Exchange Server Remote Code Execution Vulnerability"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "f38d906d-7342-40ea-92c1-6c4a2c6478c8",
    "assignerShortName": "microsoft",
    "cveId": "CVE-2021-26858",
    "datePublished": "2021-03-02T23:55:27.000Z",
    "dateReserved": "2021-02-08T00:00:00.000Z",
    "dateUpdated": "2025-10-21T23:25:52.837Z",
    "state": "PUBLISHED"
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      "dateAdded": "2021-11-03",
      "dueDate": "2022-05-03",
      "knownRansomwareCampaignUse": "Known",
      "notes": "Reference CISA\u0027s ED 21-02 (https://www.cisa.gov/news-events/directives/ed-21-02-mitigate-microsoft-exchange-premises-product-vulnerabilities) for further guidance and requirements. Note: The due date for addressing this vulnerability aligns with the requirements outlined in ED 21-02. https://nvd.nist.gov/vuln/detail/CVE-2021-26858",
      "product": "Exchange Server",
      "requiredAction": "Apply updates per vendor instructions.",
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      "vendorProject": "Microsoft",
      "vulnerabilityName": "Microsoft Exchange Server Remote Code Execution Vulnerability"
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\"versionType\": \"custom\"}], \"platforms\": [\"x64-based Systems\"]}, {\"cpes\": [\"cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_14:*:*:*:*:*:*\"], \"vendor\": \"Microsoft\", \"product\": \"Microsoft Exchange Server 2016 Cumulative Update 14\", \"versions\": [{\"status\": \"affected\", \"version\": \"15.01.0\", \"lessThan\": \"publication\", \"versionType\": \"custom\"}], \"platforms\": [\"x64-based Systems\"]}, {\"cpes\": [\"cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_4:*:*:*:*:*:*\"], \"vendor\": \"Microsoft\", \"product\": \"Microsoft Exchange Server 2019 Cumulative Update 4\", \"versions\": [{\"status\": \"affected\", \"version\": \"15.02.0\", \"lessThan\": \"publication\", \"versionType\": \"custom\"}], \"platforms\": [\"x64-based Systems\"]}, {\"cpes\": [\"cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_15:*:*:*:*:*:*\"], \"vendor\": \"Microsoft\", \"product\": \"Microsoft Exchange Server 2016 Cumulative Update 15\", \"versions\": [{\"status\": \"affected\", \"version\": \"15.01.0\", \"lessThan\": \"publication\", \"versionType\": \"custom\"}], \"platforms\": [\"x64-based Systems\"]}, {\"cpes\": [\"cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_5:*:*:*:*:*:*\"], \"vendor\": \"Microsoft\", \"product\": \"Microsoft Exchange Server 2019 Cumulative Update 5\", \"versions\": [{\"status\": \"affected\", \"version\": \"15.02.0\", \"lessThan\": \"publication\", \"versionType\": \"custom\"}], \"platforms\": [\"x64-based Systems\"]}, {\"cpes\": [\"cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_6:*:*:*:*:*:*\"], \"vendor\": \"Microsoft\", \"product\": \"Microsoft Exchange Server 2019 Cumulative Update 6\", \"versions\": [{\"status\": \"affected\", \"version\": \"15.02.0\", \"lessThan\": \"publication\", \"versionType\": \"custom\"}], \"platforms\": [\"x64-based Systems\"]}, {\"cpes\": [\"cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_16:*:*:*:*:*:*\"], \"vendor\": \"Microsoft\", \"product\": \"Microsoft Exchange Server 2016 Cumulative Update 16\", \"versions\": [{\"status\": \"affected\", \"version\": \"15.01.0\", \"lessThan\": \"publication\", \"versionType\": \"custom\"}], \"platforms\": [\"x64-based Systems\"]}, {\"cpes\": [\"cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_17:*:*:*:*:*:*\"], \"vendor\": \"Microsoft\", \"product\": \"Microsoft Exchange Server 2016 Cumulative Update 17\", \"versions\": [{\"status\": \"affected\", \"version\": \"15.01.0\", \"lessThan\": \"publication\", \"versionType\": \"custom\"}], \"platforms\": [\"x64-based Systems\"]}, {\"cpes\": [\"cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_7:*:*:*:*:*:*\"], \"vendor\": \"Microsoft\", \"product\": \"Microsoft Exchange Server 2019 Cumulative Update 7\", \"versions\": [{\"status\": \"affected\", \"version\": \"15.02.0\", \"lessThan\": \"publication\", \"versionType\": \"custom\"}], \"platforms\": [\"x64-based Systems\"]}, {\"cpes\": [\"cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_18:*:*:*:*:*:*\"], \"vendor\": \"Microsoft\", \"product\": \"Microsoft Exchange Server 2016 Cumulative Update 18\", \"versions\": [{\"status\": \"affected\", \"version\": \"15.01.0\", \"lessThan\": \"publication\", \"versionType\": \"custom\"}], \"platforms\": [\"x64-based Systems\"]}, {\"cpes\": [\"cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_19:*:*:*:*:*:*\"], \"vendor\": \"Microsoft\", \"product\": \"Microsoft Exchange Server 2016 Cumulative Update 19\", \"versions\": [{\"status\": \"affected\", \"version\": \"15.01.0\", \"lessThan\": \"publication\", \"versionType\": \"custom\"}], \"platforms\": [\"x64-based Systems\"]}, {\"cpes\": [\"cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_8:*:*:*:*:*:*\"], \"vendor\": \"Microsoft\", \"product\": \"Microsoft Exchange Server 2019 Cumulative Update 8\", \"versions\": [{\"status\": \"affected\", \"version\": \"15.02.0\", \"lessThan\": \"publication\", \"versionType\": \"custom\"}], \"platforms\": [\"x64-based Systems\"]}, {\"cpes\": [\"cpe:2.3:a:microsoft:exchange_server:2013:cumulative_update_21:*:*:*:*:*:*\"], \"vendor\": \"Microsoft\", \"product\": \"Microsoft Exchange Server 2013 Cumulative Update 21\", \"versions\": [{\"status\": \"affected\", \"version\": \"15.00.0\", \"lessThan\": \"publication\", \"versionType\": \"custom\"}], \"platforms\": [\"x64-based Systems\"]}, {\"cpes\": [\"cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_12:*:*:*:*:*:*\"], \"vendor\": \"Microsoft\", \"product\": \"Microsoft Exchange Server 2016 Cumulative Update 12\", \"versions\": [{\"status\": \"affected\", \"version\": \"15.01.0\", \"lessThan\": \"publication\", \"versionType\": \"custom\"}], \"platforms\": [\"x64-based Systems\"]}, {\"cpes\": [\"cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_8:*:*:*:*:*:*\"], \"vendor\": \"Microsoft\", \"product\": \"Microsoft Exchange Server 2016 Cumulative Update 8\", \"versions\": [{\"status\": \"affected\", \"version\": \"15.01.0\", \"lessThan\": \"publication\", \"versionType\": \"custom\"}], \"platforms\": [\"x64-based Systems\"]}, {\"cpes\": [\"cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_1:*:*:*:*:*:*\"], \"vendor\": \"Microsoft\", \"product\": \"Microsoft Exchange Server 2019 Cumulative Update 1\", \"versions\": [{\"status\": \"affected\", \"version\": \"15.02.0\", \"lessThan\": \"publication\", \"versionType\": \"custom\"}], \"platforms\": [\"x64-based Systems\"]}, {\"cpes\": [\"cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_9:*:*:*:*:*:*\"], \"vendor\": \"Microsoft\", \"product\": \"Microsoft Exchange Server 2016 Cumulative Update 9\", \"versions\": [{\"status\": \"affected\", \"version\": \"15.01.0\", \"lessThan\": \"publication\", \"versionType\": \"custom\"}], \"platforms\": [\"x64-based Systems\"]}, {\"cpes\": [\"cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_10:*:*:*:*:*:*\"], \"vendor\": \"Microsoft\", \"product\": \"Microsoft Exchange Server 2016 Cumulative Update 10\", \"versions\": [{\"status\": \"affected\", \"version\": \"15.01.0\", \"lessThan\": \"publication\", \"versionType\": \"custom\"}], \"platforms\": [\"x64-based Systems\"]}, {\"cpes\": [\"cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_11:*:*:*:*:*:*\"], \"vendor\": \"Microsoft\", \"product\": \"Microsoft Exchange Server 2016 Cumulative Update 11\", \"versions\": [{\"status\": \"affected\", \"version\": \"15.01.0\", \"lessThan\": \"publication\", \"versionType\": \"custom\"}], \"platforms\": [\"x64-based Systems\"]}], \"datePublic\": \"2021-03-02T08:00:00.000Z\", \"references\": [{\"url\": \"https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2021-26858\", \"tags\": [\"x_refsource_MISC\"]}], \"descriptions\": [{\"lang\": \"en-US\", \"value\": \"Microsoft Exchange Server Remote Code Execution Vulnerability\"}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en-US\", \"type\": \"Impact\", \"description\": \"Remote Code Execution\"}]}], \"providerMetadata\": {\"orgId\": \"f38d906d-7342-40ea-92c1-6c4a2c6478c8\", \"shortName\": \"microsoft\", \"dateUpdated\": \"2023-12-29T20:08:57.719Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2021-26858\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2025-10-21T23:25:52.837Z\", \"dateReserved\": \"2021-02-08T00:00:00.000Z\", \"assignerOrgId\": \"f38d906d-7342-40ea-92c1-6c4a2c6478c8\", \"datePublished\": \"2021-03-02T23:55:27.000Z\", \"assignerShortName\": \"microsoft\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.1"
    }
  }
}


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Taxonomy of the tags.


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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

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Detection rules are retrieved from Rulezet.

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