NCSC-2026-0234

Vulnerability from csaf_ncscnl - Published: 2026-07-14 18:31 - Updated: 2026-07-14 18:31
Summary
Kwetsbaarheden verholpen in Microsoft Exchange
Notes
The Netherlands Cyber Security Center (henceforth: NCSC-NL) maintains this page to enhance access to its information and security advisories. The use of this security advisory is subject to the following terms and conditions: NCSC-NL makes every reasonable effort to ensure that the content of this page is kept up to date, and that it is accurate and complete. Nevertheless, NCSC-NL cannot entirely rule out the possibility of errors, and therefore cannot give any warranty in respect of its completeness, accuracy or continuous keeping up-to-date. The information contained in this security advisory is intended solely for the purpose of providing general information to professional users. No rights can be derived from the information provided therein. NCSC-NL and the Kingdom of the Netherlands assume no legal liability or responsibility for any damage resulting from either the use or inability of use of this security advisory. This includes damage resulting from the inaccuracy of incompleteness of the information contained in the advisory. This security advisory is subject to Dutch law. All disputes related to or arising from the use of this advisory will be submitted to the competent court in The Hague. This choice of means also applies to the court in summary proceedings.
Feiten: Microsoft heeft kwetsbaarheden verholpen in Exchange, zowel Online als on-premise.
Interpretaties: Een kwaadwillende kan de kwetsbaarheden misbruiken om zich voor te doen als andere gebruiker, zich verhoogde rechten toe te kennen, mogelijk willekeurige code uit te voeren en zo toegang te krijgen tot gevoelige gegevens. De kwetsbaarheid in Exchange Online is inmiddels door Microsoft centraal verholpen en is opgenomen ter informatie. Hiervoor zijn geen acties benodigd. De ernstigste kwetsbaarheid in Exchange Server (on-premise) heeft een CVSS van 9.6 toegewezen gekregen en bevindt zich in Outlook Web Access. Deze kwetsbaarheid stelt een kwaadwillende in staat om een Cross-Site-Scripting-aanval (XSS) uit te voeren en zo toegang te krijgen tot de omgeving van het slachtoffer. Er is (nog) geen actief misbruik waargenomen en er is ook geen Proof-of-Concept-code (PoC) bekend, maar Microsoft geeft aan dat zij de kans op misbruik op korte termijn waarschijnlijk achten. Met name OWA-omgevingen die publiek toegankelijk zijn lopen hierdoor verhoogd risico. ``` Microsoft Exchange Online: |----------------|------|-------------------------------------| | CVE-ID | CVSS | Impact | |----------------|------|-------------------------------------| | CVE-2026-54998 | 8.80 | Verkrijgen van verhoogde rechten | |----------------|------|-------------------------------------| Microsoft Exchange Server: |----------------|------|-------------------------------------| | CVE-ID | CVSS | Impact | |----------------|------|-------------------------------------| | CVE-2026-55005 | 8.80 | Uitvoeren van willekeurige code | | CVE-2026-55006 | 7.80 | Verkrijgen van verhoogde rechten | | CVE-2026-55008 | 9.60 | Voordoen als andere gebruiker | | CVE-2026-55009 | 7.80 | Verkrijgen van verhoogde rechten | |----------------|------|-------------------------------------| ```
Oplossingen: Microsoft heeft updates beschikbaar gesteld waarmee de beschreven kwetsbaarheden worden verholpen. We raden u aan om deze updates te installeren. Meer informatie over de kwetsbaarheden, de installatie van de updates en eventuele work-arounds vindt u op: https://portal.msrc.microsoft.com/en-us/security-guidance
Kans: medium
Schade: high
CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
CWE-122: Heap-based Buffer Overflow
CWE-502: Deserialization of Untrusted Data
CWE-863: Incorrect Authorization
CWE-1220: Insufficient Granularity of Access Control
CVE-2026-54998

An incorrect authorization vulnerability in Microsoft Exchange Online enables an authorized attacker to elevate privileges over a network, potentially compromising system integrity.

8.8 (High)
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CWE-863 - Incorrect Authorization
Affected products
Product Identifier Version Remediation
vers:unknown/*
Microsoft / Microsoft Exchange Online
 vers:unknown/*
vers:unknown/*
Microsoft / Microsoft Exchange Server 2016 Cumulative Update 23
 vers:unknown/*
vers:unknown/*
Microsoft / Microsoft Exchange Server 2019 Cumulative Update 14
 vers:unknown/*
vers:unknown/*
Microsoft / Microsoft Exchange Server 2019 Cumulative Update 15
 vers:unknown/*
vers:unknown/*
Microsoft / Microsoft Exchange Server Subscription Edition RTM
 vers:unknown/*
CVE-2026-55005

A heap-based buffer overflow vulnerability in Microsoft Exchange Server enables an authorized attacker to execute arbitrary code remotely over a network.

8.8 (High)
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
CWE-122 - Heap-based Buffer Overflow
Affected products
Product Identifier Version Remediation
vers:unknown/*
Microsoft / Microsoft Exchange Online
 vers:unknown/*
vers:unknown/*
Microsoft / Microsoft Exchange Server 2016 Cumulative Update 23
 vers:unknown/*
vers:unknown/*
Microsoft / Microsoft Exchange Server 2019 Cumulative Update 14
 vers:unknown/*
vers:unknown/*
Microsoft / Microsoft Exchange Server 2019 Cumulative Update 15
 vers:unknown/*
vers:unknown/*
Microsoft / Microsoft Exchange Server Subscription Edition RTM
 vers:unknown/*
CVE-2026-55006

An insufficient granularity of access control vulnerability in Microsoft Exchange Server allows an authorized local attacker to elevate privileges.

7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CWE-1220 - Insufficient Granularity of Access Control
Affected products
Product Identifier Version Remediation
vers:unknown/*
Microsoft / Microsoft Exchange Online
 vers:unknown/*
vers:unknown/*
Microsoft / Microsoft Exchange Server 2016 Cumulative Update 23
 vers:unknown/*
vers:unknown/*
Microsoft / Microsoft Exchange Server 2019 Cumulative Update 14
 vers:unknown/*
vers:unknown/*
Microsoft / Microsoft Exchange Server 2019 Cumulative Update 15
 vers:unknown/*
vers:unknown/*
Microsoft / Microsoft Exchange Server Subscription Edition RTM
 vers:unknown/*
CVE-2026-55008

Microsoft Exchange Server contains a cross-site scripting vulnerability due to improper input neutralization during web page generation, enabling unauthorized attackers to perform network-based spoofing.

9.6 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H/E:U/RL:O/RC:C
CWE-79 - Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Affected products
Product Identifier Version Remediation
vers:unknown/*
Microsoft / Microsoft Exchange Online
 vers:unknown/*
vers:unknown/*
Microsoft / Microsoft Exchange Server 2016 Cumulative Update 23
 vers:unknown/*
vers:unknown/*
Microsoft / Microsoft Exchange Server 2019 Cumulative Update 14
 vers:unknown/*
vers:unknown/*
Microsoft / Microsoft Exchange Server 2019 Cumulative Update 15
 vers:unknown/*
vers:unknown/*
Microsoft / Microsoft Exchange Server Subscription Edition RTM
 vers:unknown/*
CVE-2026-55009

A deserialization vulnerability in Microsoft Exchange Server enables an authorized attacker to perform local privilege escalation by processing untrusted data.

7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
CWE-502 - Deserialization of Untrusted Data
Affected products
Product Identifier Version Remediation
vers:unknown/*
Microsoft / Microsoft Exchange Online
 vers:unknown/*
vers:unknown/*
Microsoft / Microsoft Exchange Server 2016 Cumulative Update 23
 vers:unknown/*
vers:unknown/*
Microsoft / Microsoft Exchange Server 2019 Cumulative Update 14
 vers:unknown/*
vers:unknown/*
Microsoft / Microsoft Exchange Server 2019 Cumulative Update 15
 vers:unknown/*
vers:unknown/*
Microsoft / Microsoft Exchange Server Subscription Edition RTM
 vers:unknown/*
References
To clipboard 

{
  "document": {
    "category": "csaf_security_advisory",
    "csaf_version": "2.0",
    "distribution": {
      "tlp": {
        "label": "WHITE"
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    "lang": "nl",
    "notes": [
      {
        "category": "legal_disclaimer",
        "text": "The Netherlands Cyber Security Center (henceforth: NCSC-NL) maintains this page to enhance access to its information and security advisories. The use of this security advisory is subject to the following terms and conditions:\n\n    NCSC-NL makes every reasonable effort to ensure that the content of this page is kept up to date, and that it is accurate and complete. Nevertheless, NCSC-NL cannot entirely rule out the possibility of errors, and therefore cannot give any warranty in respect of its completeness, accuracy or continuous keeping up-to-date. The information contained in this security advisory is intended solely for the purpose of providing general information to professional users. No rights can be derived from the information provided therein.\n\n    NCSC-NL and the Kingdom of the Netherlands assume no legal liability or responsibility for any damage resulting from either the use or inability of use of this security advisory. This includes damage resulting from the inaccuracy of incompleteness of the information contained in the advisory.\n    This security advisory is subject to Dutch law. All disputes related to or arising from the use of this advisory will be submitted to the competent court in The Hague. This choice of means also applies to the court in summary proceedings."
      },
      {
        "category": "description",
        "text": "Microsoft heeft kwetsbaarheden verholpen in Exchange, zowel Online als on-premise.",
        "title": "Feiten"
      },
      {
        "category": "description",
        "text": "Een kwaadwillende kan de kwetsbaarheden misbruiken om zich voor te doen als andere gebruiker, zich verhoogde rechten toe te kennen, mogelijk willekeurige code uit te voeren en zo toegang te krijgen tot gevoelige gegevens.\n\nDe kwetsbaarheid in Exchange Online is inmiddels door Microsoft centraal verholpen en is opgenomen ter informatie. Hiervoor zijn geen acties benodigd.\n\nDe ernstigste kwetsbaarheid in Exchange Server (on-premise) heeft een CVSS van 9.6 toegewezen gekregen en bevindt zich in Outlook Web Access. Deze kwetsbaarheid stelt een kwaadwillende in staat om een Cross-Site-Scripting-aanval (XSS) uit te voeren en zo toegang te krijgen tot de omgeving van het slachtoffer. Er is (nog) geen actief misbruik waargenomen en er is ook geen Proof-of-Concept-code (PoC) bekend, maar Microsoft geeft aan dat zij de kans op misbruik op korte termijn waarschijnlijk achten. Met name OWA-omgevingen die publiek toegankelijk zijn lopen hierdoor verhoogd risico.\n\n```\nMicrosoft Exchange Online: \n|----------------|------|-------------------------------------|\n| CVE-ID         | CVSS | Impact                              |\n|----------------|------|-------------------------------------|\n| CVE-2026-54998 | 8.80 | Verkrijgen van verhoogde rechten    | \n|----------------|------|-------------------------------------|\n\nMicrosoft Exchange Server: \n|----------------|------|-------------------------------------|\n| CVE-ID         | CVSS | Impact                              |\n|----------------|------|-------------------------------------|\n| CVE-2026-55005 | 8.80 | Uitvoeren van willekeurige code     | \n| CVE-2026-55006 | 7.80 | Verkrijgen van verhoogde rechten    | \n| CVE-2026-55008 | 9.60 | Voordoen als andere gebruiker       | \n| CVE-2026-55009 | 7.80 | Verkrijgen van verhoogde rechten    | \n|----------------|------|-------------------------------------|\n```",
        "title": "Interpretaties"
      },
      {
        "category": "description",
        "text": "Microsoft heeft updates beschikbaar gesteld waarmee de beschreven kwetsbaarheden worden verholpen. We raden u aan om deze updates te installeren. Meer informatie over de kwetsbaarheden, de installatie van de updates en eventuele work-arounds vindt u op:\n\nhttps://portal.msrc.microsoft.com/en-us/security-guidance",
        "title": "Oplossingen"
      },
      {
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        "title": "Schade"
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        "text": "Improper Neutralization of Input During Web Page Generation (\u0027Cross-site Scripting\u0027)",
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    },
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    "tracking": {
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          "title": "Summary"
        }
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        }
      ],
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            "CSAFPID-2",
            "CSAFPID-3",
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            "CSAFPID-5"
          ]
        }
      ],
      "title": "CVE-2026-55006"
    },
    {
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        "name": "Improper Neutralization of Input During Web Page Generation (\u0027Cross-site Scripting\u0027)"
      },
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        {
          "category": "other",
          "text": "Improper Neutralization of Input During Web Page Generation (\u0027Cross-site Scripting\u0027)",
          "title": "CWE-79"
        },
        {
          "category": "description",
          "text": "Microsoft Exchange Server contains a cross-site scripting vulnerability due to improper input neutralization during web page generation, enabling unauthorized attackers to perform network-based spoofing.",
          "title": "Summary"
        }
      ],
      "product_status": {
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      },
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          "url": "https://vulnerabilities.ncsc.nl/csaf/v2/2026/cve-2026-55008.json"
        }
      ],
      "scores": [
        {
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            "baseSeverity": "CRITICAL",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H/E:U/RL:O/RC:C",
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            "CSAFPID-2",
            "CSAFPID-3",
            "CSAFPID-4",
            "CSAFPID-5"
          ]
        }
      ],
      "title": "CVE-2026-55008"
    },
    {
      "cve": "CVE-2026-55009",
      "cwe": {
        "id": "CWE-502",
        "name": "Deserialization of Untrusted Data"
      },
      "notes": [
        {
          "category": "other",
          "text": "Deserialization of Untrusted Data",
          "title": "CWE-502"
        },
        {
          "category": "description",
          "text": "A deserialization vulnerability in Microsoft Exchange Server enables an authorized attacker to perform local privilege escalation by processing untrusted data.",
          "title": "Summary"
        }
      ],
      "product_status": {
        "known_affected": [
          "CSAFPID-1",
          "CSAFPID-2",
          "CSAFPID-3",
          "CSAFPID-4",
          "CSAFPID-5"
        ]
      },
      "references": [
        {
          "category": "self",
          "summary": "CVE-2026-55009 | NCSC-NL Website",
          "url": "https://vulnerabilities.ncsc.nl/csaf/v2/2026/cve-2026-55009.json"
        }
      ],
      "scores": [
        {
          "cvss_v3": {
            "baseScore": 7.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "products": [
            "CSAFPID-1",
            "CSAFPID-2",
            "CSAFPID-3",
            "CSAFPID-4",
            "CSAFPID-5"
          ]
        }
      ],
      "title": "CVE-2026-55009"
    }
  ]
}



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Taxonomy of the tags.





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.


Detection rules are retrieved from Rulezet.