MediumCVE-2026-45501

    Microsoft Exchange Server Spoofing Vulnerability (CVE-2026-45501)

    Published Last modified Sources: BSI, Msrc Update Guide, CVE.org

    What is affected, what to do

    Server-side request forgery (ssrf) in Microsoft Exchange Server allows an authorized attacker to perform spoofing over a network.

    Update Microsoft Exchange Server 2016 Cumulative Update 23 to version 15.01.2507.071, Microsoft Exchange Server 2019 Cumulative Update 14 to version 15.02.1544.043, Microsoft Exchange Server 2019 Cumulative Update 15 to version 15.02.1748.048.

    Affected
    • Microsoft Exchange Server 2016 Cumulative Update 23 lt 15.01.0.0..15.01.2507.071
    • Microsoft Exchange Server 2019 Cumulative Update 14 lt 15.02.0.0..15.02.1544.043
    • Microsoft Exchange Server 2019 Cumulative Update 15 lt 15.02.0.0..15.02.1748.048
    • Microsoft Exchange Server Subscription Edition RTM lt 15.02.0.0..15.02.2562.045
    Fixed in
    • Microsoft Exchange Server 2016 Cumulative Update 23 15.01.2507.071
    • Microsoft Exchange Server 2019 Cumulative Update 14 15.02.1544.043
    • Microsoft Exchange Server 2019 Cumulative Update 15 15.02.1748.048
    • Microsoft Exchange Server Subscription Edition RTM 15.02.2562.045

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    6.5

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v3

    6.5

    CVSS v3

    Severity Medium on the scale from 0 to 10.

    Source: BSI, Msrc Update Guide, CVE.org

    0.4 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 34.3

    Show all metrics
    Severity
    Medium
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    60.64 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    no public PoC known
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    6.5 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    6.5
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    0.4 %
    Low — model estimates < 1% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    34.3
    Elevated — this CVE ranks above at least 10% of all CVEs scored today.
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    —
    Published
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-918

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Handle the vulnerability in regular vulnerability handling under Art. 21(2)(e) NIS2.
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    Server-side request forgery (ssrf) in Microsoft Exchange Server allows an authorized attacker to perform spoofing over a network.

    Source: BSI WID Portal, BSI CSAF, Microsoft Security Update Guide, cvelistv5, NVD (NIST)

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    MicrosoftMicrosoft Exchange Server 2016 Cumulative Update 23
    • 15.01.0.0 – < 15.01.2507.071
    • 15.01.2507.071
    MicrosoftMicrosoft Exchange Server 2019 Cumulative Update 14
    • 15.02.0.0 – < 15.02.1544.043
    • 15.02.1544.043
    MicrosoftMicrosoft Exchange Server 2019 Cumulative Update 15
    • 15.02.0.0 – < 15.02.1748.048
    • 15.02.1748.048
    MicrosoftMicrosoft Exchange Server Subscription Edition RTM
    • 15.02.0.0 – < 15.02.2562.045
    • 15.02.2562.045
    microsoftexchange_server
    • 2016
    • 2019
    • —
    • —
    microsoftexchange_server_subscription_edition
    • < 15.02.2562.043
    • 15.02.2562.043
    MicrosoftExchange
    • Server
    • Server Subscription Edition RTM
    • —
    • —

    Vendors and products

    Weakness classes (CWE)

    • CWE-918Server-Side Request Forgery (SSRF)

      Base

      The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination.

      Entry at MITRE CWE-918

    References & sources

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    1. Record modifiedMicrosoft

      Description added or changed

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionchanged
      Improper neutralization of input during web page generation ('cross-site scripting') in Microsoft Exchange Server allows an unauthorized attacker to perform spoofing over a network.
      Server-side request forgery (ssrf) in Microsoft Exchange Server allows an authorized attacker to perform spoofing over a network.

      Source identifier: secure@microsoft.com

    2. Initial analysis by NVDNVD

      Newly listed as affected:

      CVSS V3.1: AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

      Weakness type: CWE-79

      Show 4 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      CVSSadded
      —
      AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
      Weakness type (CWE)added
      —
      CWE-79
      Product configurationadded
      —
      OR *cpe:2.3:a:microsoft:exchange_server:2016:cumulative_update_23:*:*:*:*:*:* *cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_14:*:*:*:*:*:* *cpe:2.3:a:microsoft:exchange_server:2019:cumulative_update_15:*:*:*:*:*:* *cpe:2.3:a:microsoft:exchange_server_subscription_edition:*:*:*:*:*:*:*:* versions up to (excluding) 15.02.2562.043
      Reference typeadded
      —
      Microsoft Corporation: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-45501 Types: Vendor Advisory

      Source identifier: nvd@nist.gov

    One NVD translation into another language is hidden.

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