Microsoft Exchange Server Privilege Escalation Vulnerability (CVE-2018-8581)
Published In CISA KEV since Sources: CVE.org
What is affected, what to do
An elevation of privilege vulnerability exists in Microsoft Exchange Server, aka "Microsoft Exchange Server Elevation of Privilege Vulnerability." This affects Microsoft Exchange Server.
The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. The available sources name no fixed version. Check the vendor guidance in the references below. Immediate actions, mitigation and detection rules are in the runbook below.
- Affected
- Microsoft Exchange Server
eq 2010..2010 - Microsoft Exchange Server
eq 2013..2013 - Microsoft Exchange Server
eq 2016..2016 - Microsoft Exchange Server
eq 2019..2019
- Microsoft Exchange Server
Not sure whether and how you are affected? Ask a question about this vulnerability
Metrics
7.4
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: NVD, CVSS v3
7.4
CVSS v3
Severity High on the scale from 0 to 10.
Source: CVE.org
27.6 %
EPSS score
Elevated — model estimates 10-50% exploitation likelihood.
Source: FIRST EPSS, percentile 98.1
Show all metrics
- Severity
- Critical
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- 238.96 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- actively exploited
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- 7.4 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- 7.4
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- 27.6 %
- Elevated — model estimates 10-50% 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- 98.1
- Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
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- Actively exploited
- Published
In CISA KEV since
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- CISA assessment (SSVC)
- Exploitation: active · not automatable · Technical impact: total
- Source: CISA Vulnrichment, as of 4 February 2025
Response and mitigation
Why act now?
Prioritisation rationale
This is "PrivExchange": an SSRF in EWS push notifications chained with NTLM relay. It lets anyone holding a single mailbox abuse Exchange's historically over-privileged AD rights to take over the entire domain. The ransomware-use flag fits that profile, because the chain delivers domain-admin-equivalent access within minutes and with it the foothold for estate-wide encryption. Despite its nominally high attack complexity, it sits among the CVEs most likely to be exploited, because public tooling (privexchange.py, ntlmrelayx) makes the attack trivial. Treat any on-premises Exchange estate lacking the February 2019 CUs or cleaned-up AD ACLs as critical. That explicitly includes hybrid deployments that keep a residual Exchange server for management.
Runbook step 1
Immediate response (0-24 h)
- Verify and update the patch level of every Exchange server: Apply the security update for CVE-2018-8581. The complete fix shipped with the cumulative updates from February 2019 onward. Look up the exact CU/RU per Exchange generation in the Microsoft Security Update Guide. Servers still this far behind are almost certainly missing later critical Exchange fixes (ProxyLogon/ProxyShell), so treat them as potentially compromised.
- Strip excessive Exchange AD permissions: Check whether
Exchange Windows PermissionsorExchange Trusted Subsystemstill holdsWriteDaclon the domain root object. If it does, reduce those rights per Microsoft guidance (split-permissions model or Microsoft's remediation script). These rights are what turns this bug into a domain takeover. - Apply the interim workaround if patching must wait: On every Exchange server, delete the
DisableLoopbackCheckvalue underHKLM\SYSTEM\CurrentControlSet\Control\Lsaand reboot. This is Microsoft's original stop-gap. - Hunt for prior compromise on the domain root: Review the domain object ACL for unexpected ACEs granting
DS-Replication-Get-Changes/-All(e.g.Get-Acl "AD:DC=corp,DC=local"). Any non-DC principal holding replication rights is a top-priority finding. - If DCSync is suspected: Reset
krbtgttwice, with replication time between the resets. Then rotate privileged accounts and Exchange machine accounts, and invoke the domain-compromise IR procedure.
Runbook step 2
Mitigation layers
- Network segmentation / egress: Block Exchange servers from opening arbitrary outbound HTTP/HTTPS connections to internal hosts or the internet. Allow-list only what is required (smarthost, updates, hybrid endpoints). The exploit coerces an NTLM-authenticated HTTP callback from Exchange to the attacker's listener.
- NTLM relay hardening: Enforce LDAP signing and LDAP channel binding on all domain controllers. Require SMB signing domain-wide and enable Extended Protection for Authentication (EPA) on Exchange/IIS. This breaks the relay to LDAP.
- EWS configuration: Restrict or disable push subscriptions via throttling policy, e.g.
New-ThrottlingPolicy -Name NoEwsSubs -EwsMaxSubscriptions 0, assigned to mailboxes that don't need them. Limit external EWS access via client access rules or the reverse proxy. - IAM / least privilege: Audit NTLM usage with the GPO "Network security: Restrict NTLM", then reduce it. Monitor Exchange machine accounts as tier-0-adjacent. Reset weak mailbox passwords, since the attack realistically needs one valid mailbox credential.
- WAF/IPS: Inspect requests to
/EWS/Exchange.asmxcarryingSubscribe/PushSubscriptionRequestbodies. Alert on or block callbackURLvalues pointing to non-approved hosts.
Runbook step 3
Detection rules
- DCSync by a non-DC (Security Event 4662):
Propertiescontains1131f6aa-9c07-11d1-f79f-00c04fc2dcd2or1131f6ad-9c07-11d1-f79f-00c04fc2dcd2on the domain object, from a non-DC subject. KQL:SecurityEvent | where EventID==4662 and Properties has "1131f6ad" and SubjectUserName !endswith "$". Then extend the filter to exclude DC machine accounts. - Domain root ACL change (Event 5136):
AttributeLDAPDisplayName == "nTSecurityDescriptor"on the domain object, especially when the change is made by an Exchange machine account (EXCH01$). - Exchange machine account NTLM logon (Event 4624):
LogonType 3,AuthenticationPackageName NTLM,TargetUserName= Exchange computer account, with a sourceIpAddressthat is not an Exchange server. This is a textbook relay indicator. - EWS/IIS logs: Search
%ExchangeInstallPath%Logging\Ewsand the IIS logs forPOST /EWS/Exchange.asmxwith Subscribe operations whose callback URL points to unusual internal IPs or ports. Sigma shape:cs-uri-stem|endswith: '/EWS/Exchange.asmx'correlated with an EWSSubscribeto an unknown URL. - Network (Zeek/Suricata): Outbound HTTP from Exchange carrying
Authorization: NTLMto non-infrastructure hosts. This is typically followed shortly by LDAP binds for the same account from a foreign source IP.
- DCSync by a non-DC (Security Event 4662):
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- Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
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- Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
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
An elevation of privilege vulnerability exists in Microsoft Exchange Server, aka "Microsoft Exchange Server Elevation of Privilege Vulnerability." This affects Microsoft Exchange Server.
Source: NVD (NIST), cvelistv5, CISA KEV Catalog
Affected products
The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.
| Affected versions | Fixed in | ||
|---|---|---|---|
| Microsoft | Microsoft Exchange Server |
|
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| microsoft | exchange_server |
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Vendors and products
Public exploit references
Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.
| CISA KEV Catalog | CISA Known Exploited Vulnerability (opens in a new tab)cisa.gov | actively exploited |
References & sources
- securitytracker.com1042141Vulnerability database, x_refsource_SECTRACK, Broken link, Third-party advisory, Vulnerability database
- securityfocus.com105837Vulnerability database, x_refsource_BID, Broken link, Third-party advisory, Vulnerability database
- portal.msrc.microsoft.comen-US/security-guidance/advisory/CVE-2018-8581x_refsource_CONFIRM, Patch, Vendor advisory
- cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2018-8581government-resource, US government resource
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<a href="https://intel.neosec.eu/en/cve/CVE-2018-8581"><img src="https://intel.neosec.eu/badge/cve/CVE-2018-8581.svg?lang=en" alt="CVE-2018-8581 – NEOSEC Intel" height="20"></a>