Microsoft Exchange Server Remote Code Execution Vulnerability (CVE-2022-41082)
Published In CISA KEV since Sources: SingCERT, CVE.org
- Actively exploited
- Source: ANSSI / CERT-FR, CSA/SingCERT How we classify
- Ransomware
- Public exploit
What is affected, what to do
Microsoft Exchange Server Remote Code Execution Vulnerability
The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. Update Microsoft Exchange Server 2013 Cumulative Update 23 to version 15.00.1497.044, Microsoft Exchange Server 2016 Cumulative Update 22 to version 15.01.2375.037, Microsoft Exchange Server 2019 Cumulative Update 11 to version 15.02.0986.036. Immediate actions, mitigation and detection rules are in the runbook below.
- Affected
- Microsoft Exchange Server 2013 Cumulative Update 23
lt 15.00.0..15.00.1497.044 - Microsoft Exchange Server 2016 Cumulative Update 22
lt 15.0.0..15.01.2375.037 - Microsoft Exchange Server 2019 Cumulative Update 11
lt 15.02.0..15.02.0986.036 - Microsoft Exchange Server 2019 Cumulative Update 12
lt 15.02.0..15.02.1118.020 - Microsoft Exchange Server 2016 Cumulative Update 23
lt 15.01.0..15.01.2507.016
- Microsoft Exchange Server 2013 Cumulative Update 23
- Fixed in
- Microsoft Exchange Server 2013 Cumulative Update 23
15.00.1497.044 - Microsoft Exchange Server 2016 Cumulative Update 22
15.01.2375.037 - Microsoft Exchange Server 2019 Cumulative Update 11
15.02.0986.036 - Microsoft Exchange Server 2019 Cumulative Update 12
15.02.1118.020 - Microsoft Exchange Server 2016 Cumulative Update 23
15.01.2507.016
- Microsoft Exchange Server 2013 Cumulative Update 23
Not sure whether and how you are affected? Ask a question about this vulnerability
Metrics
8.0
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: NVD, CVSS v3
8.0
CVSS v3
Severity High on the scale from 0 to 10.
Source: SingCERT, CVE.org
99.97 %
EPSS score
High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
Source: FIRST EPSS, percentile 99.98
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- 246.45 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 exploitedSource: ANSSI / CERT-FR, CSA/SingCERT How we classify
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- 8.0 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- 8.0
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- 99.97 %
- High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
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- 99.98
- 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
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-502
Response and mitigation
Why act now?
Prioritisation rationale
ProxyNotShell is on KEV because chaining the SSRF (CVE-2022-41040) with this PowerShell-remoting RCE gives SYSTEM-level code execution on Exchange using nothing more than an ordinary mailbox account. Such accounts are trivially obtained through password spraying or phishing. The CVSS vector formally indicates adjacent-network access, but the SSRF chain makes it reachable in practice through any internet-facing OWA/Autodiscover instance. Exploitation likelihood is among the highest of any CVE, and CISA confirms use in ransomware campaigns, often via the OWASSRF bypass of the URL Rewrite mitigation. For any organisation running on-premises or hybrid Exchange, treat this as a top-priority emergency change. An unpatched, externally reachable server should be presumed compromised until proven otherwise, with potential NIS2 reporting obligations.
Runbook step 1
Immediate response (0-24 h)
- Install the November 2022 Exchange Security Update (or later). These builds close ProxyNotShell (CVE-2022-41082 plus the SSRF link CVE-2022-41040): Exchange 2013 CU23 ≥ 15.00.1497.044, Exchange 2016 CU22 ≥ 15.01.2375.037, CU23 ≥ 15.01.2507.016, Exchange 2019 CU11 ≥ 15.02.0986.036, CU12 ≥ 15.02.1118.020. Look up the KB number in the vendor advisory. Verify the build with
Get-ExchangeServer | fl Name,AdminDisplayVersionand the file version ofExSetup.exe. Servers on older CUs must move to a supported CU first. - Treat Exchange 2013 as a special risk. It has been end-of-life since April 2023 and receives no further fixes. Plan migration now, and until then isolate it and publish it only through a pre-authenticating reverse proxy.
- Until patched, remove direct internet exposure of OWA/ECP/Autodiscover on TCP 443. Publish only through a pre-authenticating reverse proxy (e.g. Entra Application Proxy, F5 APM). Block the
/powershellendpoint externally altogether. - Run a compromise assessment before declaring the server clean. Run Microsoft's Exchange On-premises Mitigation Tool and Health Checker. Hunt for
.aspxwebshells inFrontEnd\HttpProxy\owa\auth\,\ecp\andinetpub\wwwroot\aspnet_client\. - Rotate credentials. The chain needs any valid mailbox account. Reset accounts that appear in Autodiscover/PowerShell log hits. If you find signs of compromise, also rotate Exchange service accounts and privileged AD accounts, since Exchange typically holds broad AD rights.
- Disable Remote PowerShell for non-admins:
Set-User -Identity <user> -RemotePowerShellEnabled $false, scripted across all non-admin mailboxes.
- Install the November 2022 Exchange Security Update (or later). These builds close ProxyNotShell (CVE-2022-41082 plus the SSRF link CVE-2022-41040): Exchange 2013 CU23 ≥ 15.00.1497.044, Exchange 2016 CU22 ≥ 15.01.2375.037, CU23 ≥ 15.01.2507.016, Exchange 2019 CU11 ≥ 15.02.0986.036, CU12 ≥ 15.02.1118.020. Look up the KB number in the vendor advisory. Verify the build with
Runbook step 2
Mitigation layers
- Network segmentation: Put Exchange in a dedicated DMZ/server zone. Restrict egress to defined destinations (smarthost, Microsoft update endpoints). Deny arbitrary outbound traffic from
w3wp.exeto disrupt payload staging and C2. - IIS URL Rewrite / WAF: Block requests matching
.*autodiscover\.json.*powershell.*(case-insensitive, on{UrlDecode:{REQUEST_URI}}). Microsoft's original rule was bypassed several times, so also block/owa/mastermailbox/powershell, which the OWASSRF variant (CVE-2022-41080) uses to evade the Autodiscover rule. This is a stopgap, not a patch substitute. - Exchange Emergency Mitigation Service (EEMS): Confirm the service is enabled and can reach
officeclient.microsoft.com. This is what lets Microsoft-issued emergency mitigations apply automatically. - Endpoint hardening: Enable the ASR rule "Block Webshell creation for Servers". Set EDR policy to block, or at minimum alert on, child processes of
w3wp.exe(MSExchange*AppPool). Keep Exchange AMSI integration on. - IAM / least privilege: Review Exchange split permissions and prune excess membership in "Organization Management" and "Exchange Trusted Subsystem". Classify Exchange servers as Tier 0 in your AD tiering model.
- Network segmentation: Put Exchange in a dedicated DMZ/server zone. Restrict egress to defined destinations (smarthost, Microsoft update endpoints). Deny arbitrary outbound traffic from
Runbook step 3
Detection rules
- IIS access logs (W3SVC1/W3SVC2): Look for requests where
cs-uri-stemis/autodiscover/autodiscover.jsonandcs-uri-querycontainspowershell, especially with status 200/302. Also watch for/owa/mastermailbox/powershell. SPL:index=iis cs_uri_stem="*autodiscover.json*" cs_uri_query="*powershell*" | stats count by c_ip, cs_username. - Exchange HttpProxy logs (
%ExchangeInstallPath%Logging\HttpProxy\Autodiscover\and\PowerShell\): Entries routing to/powershellviaAnchorMailbox/RoutingHintfrom external source IPs are a strong indicator. - EDR / Sysmon EID 1 (process ancestry): Watch for
w3wp.exe(command line containingMSExchangePowerShellAppPoolorMSExchangeAutodiscoverAppPool) spawningcmd.exe,powershell.exe,certutil.exe,rundll32.exeormshta.exe. KQL:DeviceProcessEvents | where InitiatingProcessFileName =~ "w3wp.exe" and InitiatingProcessCommandLine has "MSExchange" and FileName in~ ("cmd.exe","powershell.exe","certutil.exe"). - Sysmon EID 11 / file monitoring: Alert on new
.aspx,.ashxor.asmxfiles written byw3wp.exeunderFrontEnd\HttpProxy\owa\auth\,ecp\oraspnet_client\. - Windows events: Use PowerShell Script Block Logging (EID 4104) to catch suspicious cmdlets such as
New-MailboxExportRequestorAdd-RoleGroupMember. Check the MSExchange Management log for unusual cmdlet execution. Correlate EID 4720/4728 (account creation or privileged group changes) shortly after webshell indicators.
- IIS access logs (W3SVC1/W3SVC2): Look for requests where
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
Microsoft Exchange Server Remote Code Execution Vulnerability
Source: CSA/SingCERT, NVD (NIST), cvelistv5, CISA KEV Catalog, CVE.org (MITRE)
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 2013 Cumulative Update 23 |
|
|
| Microsoft | Microsoft Exchange Server 2016 Cumulative Update 22 |
|
|
| Microsoft | Microsoft Exchange Server 2016 Cumulative Update 23 |
|
|
| Microsoft | Microsoft Exchange Server 2019 Cumulative Update 11 |
|
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| Microsoft | Microsoft Exchange Server 2019 Cumulative Update 12 |
|
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| microsoft | exchange_server |
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Vendors and products
- Microsoft Microsoft Exchange Server
- Microsoft Microsoft Exchange Server 2013 Cumulative Update 23
- Microsoft Microsoft Exchange Server 2016 Cumulative Update 22
- Microsoft Microsoft Exchange Server 2016 Cumulative Update 23
- Microsoft Microsoft Exchange Server 2019 Cumulative Update 11
- Microsoft Microsoft Exchange Server 2019 Cumulative Update 12
Weakness classes (CWE)
CWE-502Deserialization of Untrusted Data
Base
The product deserializes untrusted data without sufficiently ensuring that the resulting data will be valid.
Entry at MITRE CWE-502
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 | |
| CSA/SingCERT | [UPDATE] Zero-day Vulnerabilities Affecting Microsoft Exchange Server (opens in a new tab)CSA/SingCERT | actively exploited | |
| ANSSI / CERT-FRLicence Ouverte 2.0, as of | CERTFR-2022-ALE-008 – [MaJ] Multiples vulnérabilités dans Microsoft Exchange (clôturée 2023-03-14) (opens in a new tab)cert.cyber.gouv.fr | actively exploited | |
| Packet Storm | Microsoft Exchange ProxyNotShell Remote Code Execution (opens in a new tab)packetstormsecurity.com | PoC (publicly reported)reported, not verified | — |
References & sources
- Microsoft Security Update GuideMicrosoft Exchange Server Remote Code Execution VulnerabilityVendor advisory, Vendor advisory
- vicarius.iovsociety/posts/cve-2022-41082-microsoft-exchange-server-remote-…Third-party advisory
- vicarius.iovsociety/posts/cve-2022-41082-microsoft-exchange-server-remote-…Third-party advisory
- portal.msrc.microsoft.comen-US/security-guidance/advisory/CVE-2022-41082x_transferred, Patch, Vendor advisory
- kb.cert.orgVU#915563Third-party advisory, x_transferred, Third-party advisory, US government resource
- packetstormsecurity.comfiles/170066/Microsoft-Exchange-ProxyNotShell-Remote-Code-Execu…x_transferred, Exploit, Third-party advisory, Vulnerability database
- secpod.comblog/microsoft-november-2022-patch-tuesday-patches-65-vulnerabi…x_transferred, Third-party advisory
- cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2022-41082government-resource, US government resource
- cert.cyber.gouv.frANSSI / CERT-FR: CERTFR-2022-ALE-008 – [MaJ] Multiples vulnérabilités dans Microsoft Exchange (clôturée 2023-03-14)cert-fr
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