Evidence used
- No CISA KEV confirmation is currently recorded.
- EPSS is 1.01% for the current model date.
BlackTreeCVE IntelligenceFull vulnerability report · 2026
CVE-2026-55005High confidence
Microsoft Exchange Server Remote Code Execution Vulnerability
Microsoft · Microsoft Exchange Server 2016 Cumulative Update 23
8.8HighCVSS 3.1
Within 7 days
Patch availableHigh technical severity; prioritise exposed affected systems while verifying vendor guidance.
R
Open reassessment dashboard →Operational reassessment
Published severity in operational context
Published severityHigh→Operational priority:High, unchanged from published severity.unchanged
Compensating controls
- Validate the affected product branch and deploy the verified fixed release.
- Restrict the affected network interface to trusted sources where business-safe.
- Monitor vendor guidance and exploitation sources for a material change.
Verification
- Confirm that the asset runs Microsoft Microsoft Exchange Server 2016 Cumulative Update 23 and falls inside the recorded affected range.
- Verify the installed build against the product-specific fixed version after deployment.
- Validate exposure, authentication requirements and compensating controls in the actual environment.
- Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
High technical severity; prioritise exposed affected systems while verifying vendor guidance.
Patch available01
What, why and how
Heap-based buffer overflow in Microsoft Exchange Server allows an authorized attacker to execute code over a network.
What
Heap-based buffer overflow in Microsoft Exchange Server allows an authorized attacker to execute code over a network.
Why
A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().
How
An attacker operating through a network path may attempt exploitation with low privileges. If successful, the issue may execute code or commands in the affected security context.
What
Heap-based buffer overflow in Microsoft Exchange Server allows an authorized attacker to execute code over a network.
Why
A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().
How
An attacker operating through a network path may attempt exploitation with low privileges. If successful, the issue may execute code or commands in the affected security context.
02
Exploit reality and attack path
CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.
Observed exploitation No confirmed evidence
?
Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.
Public PoC / exploit material None recorded
?
Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.
- Likely attack path
- a network path → Heap-based Buffer Overflow → execute code or commands in the affected security context
- Attack surface
- Network
- Privileges required
- Low: a basic authenticated account is required
- User interaction
- None
- Attack complexity
- Low: no specialised conditions are recorded
- Security boundary
- Unchanged: impact remains within the vulnerable component's security authority
- Weakness
?
CWE means Common Weakness Enumeration: a standard category for the underlying weakness. - CWE-122 ↗
CWE-122: Heap-based Buffer Overflow. A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().
- CVSS vector
?
CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity. CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:CCommon Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.
AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRLowPrivileges required: The attacker needs basic user-level privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CHighConfidentiality impact: A successful attack can cause a major loss.IHighIntegrity impact: A successful attack can cause a major loss.AHighAvailability impact: A successful attack can cause a major loss.- Post-exploitation / living off the land
- After compromise, an attacker may use built-in shells, scripting engines, scheduled tasks and native network utilities for discovery, persistence or movement. This is a plausible LoTL path, not evidence that it has occurred for every attack.
03
Patch and workaround
Operational remediation based on structured source evidence.
- Status
?
Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change. - Patch available
- Affected
- Microsoft Exchange Server 2016 Cumulative Update 23: 15.01.0.0 < 15.01.2507.071
- Microsoft Exchange Server 2019 Cumulative Update 14: 15.02.0.0 < 15.02.1544.043
- Microsoft Exchange Server 2019 Cumulative Update 15: 15.02.0.0 < 15.02.1748.048
- Microsoft Exchange Server Subscription Edition RTM: 15.02.0.0 < 15.02.2562.045
- Action
- Review the linked authoritative reference and apply the recorded fixed release appropriate to the affected product branch.
- Workaround
- No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
Official vendor articles4 stored documents
Linked articles are downloaded and versioned as source evidence. A CVE mention or approved update relationship does not, by itself, verify a fix for every product branch.
- Description of the security update for Microsoft Exchange Server Subscription Edition RTM July 14, 2026 (KB5103212) | Microsoft Support →Original publisher ↗Searchable text snapshot · Captured 17 Oct 2026Description of the security update for Microsoft Exchange Server Subscription Edition RTM: July 14, 2026 (KB5103212) Applies To Exchange Server SE This security update resolves vulnerabilities in Microsoft Exchange Server. To learn more about these vulnerabilities, see the following Common Vulnerabilities and Exposure
- Description of the security update for Microsoft Exchange Server 2019 CU15 July 14, 2026 (KB5103213) | Microsoft Support →Original publisher ↗Searchable text snapshot · Captured 17 Oct 2026Description of the security update for Microsoft Exchange Server 2019 CU15: July 14, 2026 (KB5103213) Applies To Exchange Server 2019 This security update resolves vulnerabilities in Microsoft Exchange Server. To learn more about these vulnerabilities, see the following Common Vulnerabilities and Exposures (CVE): CVE-
- Description of the security update for Microsoft Exchange Server 2019 CU14 July 14, 2026 (KB5103214) | Microsoft Support →Original publisher ↗Searchable text snapshot · Captured 17 Oct 2026Description of the security update for Microsoft Exchange Server 2019 CU14: July 14, 2026 (KB5103214) Applies To Exchange Server 2019 This security update resolves vulnerabilities in Microsoft Exchange Server. To learn more about these vulnerabilities, see the following Common Vulnerabilities and Exposures (CVE): CVE-
- Description of the security update for Microsoft Exchange Server 2016 CU23 July 14, 2026 (KB5103215) | Microsoft Support →Original publisher ↗Searchable text snapshot · Captured 17 Oct 2026Description of the security update for Microsoft Exchange Server 2016 CU23: July 14, 2026 (KB5103215) Applies To Exchange Server 2016 This security update resolves vulnerabilities in Microsoft Exchange Server. To learn more about these vulnerabilities, see the following Common Vulnerabilities and Exposures (CVE): CVE-
04
Evidence and provenance
Published 14 Jul 2026 · Last source change 8 Oct 2026, 18:13 UTC · CWE-122 · Heap-based Buffer Overflow
CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source FIRST · tracked since 2026-08-14
?
The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.European sourceENISA EUVD · EUVD-2026-44024
Product sourceCNA
Remediation sourceCVE/CNA references
CWE sourceOther authority
NVD statusNVD enriched
Core structured fields are present and their contributing authorities are shown above.
Material change intelligence
View recent updates ↗What changed after publication
- Affected versionsThe structured affected or fixed version information changed.CNA ↗
- Before
- 15.01.0.0 < 15.01.2507.071; 15.02.0.0 < 15.02.1544.043; 15.02.0.0 < 15.02.1748.048; 15.02.0.0 < 15.02.2562.045 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
- After
- Microsoft Exchange Server 2016 Cumulative Update 23: 15.01.0.0 < 15.01.2507.071; Microsoft Exchange Server 2019 Cumulative Update 14: 15.02.0.0 < 15.02.1544.043; Microsoft Exchange Server 2019 Cumulative Update 15: 15.02.0.0 < 15.02.1748.048; Microsoft Exchange Server Subscription Edition RTM: 15.02.0.0 < 15.02.2562.045 · Fixed: No fixed version is explicitly recorded in the structured CVE data.
Technical terms and abbreviations used in this report
- CVE
- Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
- CVSS
- Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
- EPSS
- Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
- CWE
- Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
- CNA
- CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
- CISA ADP
- Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
- NVD
- National Vulnerability Database: NIST's enrichment service for CVE records.
- CERT / CSIRT
- A computer security incident response team that publishes warnings or coordinates incident response.
- PoC
- Proof of concept: public material that demonstrates or helps reproduce exploitation.
- CSAF
- Common Security Advisory Framework: a machine-readable format for security advisories.
- LoTL
- Living off the land: abuse of legitimate tools or system functions during an attack.