NextGen Healthcare Mirth Connect Deserialization of Untrusted Data Vulnerability (CVE-2023-43208)
Published In CISA KEV since Sources: SingCERT, pwn.watch, CVE.org
- Actively exploited
- Source: CSA/SingCERT How we classify
- Ransomware
- Public exploit
What is affected, what to do
NextGen Healthcare Mirth Connect before version 4.4.1 is vulnerable to unauthenticated remote code execution. Note that this vulnerability is caused by the incomplete patch of CVE-2023-37679.
The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. Update NextGen Healthcare Mirth Connect to version 4.4.1. Immediate actions, mitigation and detection rules are in the runbook below.
- Affected
- NextGen Healthcare Mirth Connect
lt *..4.4.1
- NextGen Healthcare Mirth Connect
- Fixed in
- NextGen Healthcare Mirth Connect
4.4.1
- NextGen Healthcare Mirth Connect
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Metrics
9.8
Priority
XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.
Source: NVD, CVSS v3
9.8
CVSS v3
Severity Critical on the scale from 0 to 10.
Source: SingCERT, pwn.watch, CVE.org
85.4 %
EPSS score
High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
Source: FIRST EPSS, percentile 99.72
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- 257.26 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: 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- 9.8 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- 9.8
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- 85.4 %
- 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- 99.72
- 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
Response and mitigation
Why act now?
Prioritisation rationale
This CVE sits on KEV because it is network-reachable without authentication or user interaction and, per CISA, is actively used in ransomware campaigns targeting healthcare providers — directly relevant for NIS2-regulated hospitals and medical centres. Exploitation likelihood ranks among the highest in the entire CVE corpus, with public exploits and a Metasploit module available. Treat it as P1/critical for any internet-exposed Mirth instance (patch within 24 h; take offline otherwise), P2 for internally reachable instances accessible from general client networks. Combine the rating with the data classification of the HL7/FHIR flows the instance handles — when patient data is in scope, GDPR and NIS2/BSI notification duties materially raise the business risk.
Runbook step 1
Immediate response (0-24 h)
- Upgrade Mirth Connect to version 4.4.1 or later immediately (NextGen Healthcare vendor patch). The earlier fix for CVE-2023-37679 was incomplete — any build below 4.4.1 remains exploitable even if previous patches were applied.
- If patching cannot happen today: firewall the admin and listener ports (default TCP 8443 for the administrator API, 8080/8443 for HTTP/HTTPS listeners) to a dedicated admin VLAN or VPN jumphost only. No internet exposure, period.
- Run a Shodan/Censys sweep of your external IP space for exposed Mirth instances; take any hit offline or front it with a reverse proxy enforcing client certificates.
- Rotate every credential stored in Mirth (database connections, channel credentials, API keys, LDAP bind accounts). Successful RCE runs as the Mirth service account and exposes mcserver.vmoptions plus any configured secrets.
- Audit the Mirth service account at the OS level: if it runs as root or SYSTEM, switch to a dedicated least-privilege account immediately and tighten filesystem ACLs on the install directory.
- Loop in incident response and the data protection officer early. Mirth deployments typically process HL7/FHIR patient data, so a compromise usually triggers GDPR Art. 33 and NIS2 reporting obligations.
Runbook step 2
Mitigation layers
- Network segmentation: place Mirth hosts in a dedicated healthcare-integration VLAN with strict egress filtering. Allow outbound only to known HL7 peers, DB backends and monitoring. No direct internet egress — this is what breaks reverse shells and C2 beacons after a successful deserialisation exploit.
- WAF/reverse proxy in front of Mirth: block HTTP POST requests whose body contains Java serialisation magic bytes (
AC ED 00 05, Base64-encodedrO0AB) or Content-Typeapplication/xmlwith suspicious XStream markers. Cap request body size at a realistic HL7 message volume. - Enable IPS signatures for XStream and Java deserialisation gadget chains (CommonsBeanutils, CommonsCollections, Spring-AOP). Emerging Threats and Snort both publish SIDs for CVE-2023-43208 and the related CVE-2023-37679.
- Endpoint hardening: an AppArmor/SELinux profile (Linux) or WDAC policy (Windows) for the Mirth Java process that denies spawning cmd.exe, powershell.exe, bash, sh, wget, curl, python. This dramatically limits post-exploitation payload options.
- IAM: force MFA on Mirth administrator accounts via a fronting reverse proxy (Keycloak, Azure App Proxy, similar). Disable local Mirth admin accounts where feasible and delegate to LDAP/SAML.
- Backup integrity: ensure offline backups of Mirth configuration, channel definitions and the backing database (CISA KEV flags this CVE as used in ransomware campaigns). Follow 3-2-1, with at least one immutable copy.
Runbook step 3
Detection rules
- Zeek/Suricata: HTTP POST to Mirth paths (
/api/,/) whose body carries the Base64 signaturerO0ABor XStream markers such as<java.or<dynamic-proxy>. Sigma shape:selection: http.method: POST AND http.request.body|contains: "rO0AB". - Sysmon EID 1 / auditd execve: Java process (
java,mcserver) as parent of shell or download tooling (cmd.exe,powershell.exe,/bin/sh,curl,wget,certutil,bitsadmin). KQL:DeviceProcessEvents | where InitiatingProcessFileName in~ ("java.exe","java") and FileName in~ ("powershell.exe","cmd.exe","bash","sh"). - Sysmon EID 3 / Zeek conn.log: outbound connections from the Mirth host to non-whitelisted destinations, especially TCP 4444, 1337, 8888 or paste/transfer services.
- Filesystem monitoring (Sysmon EID 11, auditd): new files under the Mirth install directory —
.jsp,.class,.jar,.sh,.py— that did not originate from a patching workflow. - Mirth application logs (
logs/mirth.log,logs/mirth-cli.log): deserialisation exceptions, XStream ConversionException, ClassCastException correlated with HTTP request processing — these frequently appear as side effects of failed or chained exploit attempts. Sigma:selection: log.file: "mirth.log" AND message|contains: ["XStream","CannotResolveClassException","deserializ"].
- Zeek/Suricata: HTTP POST to Mirth paths (
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
NextGen Healthcare Mirth Connect before version 4.4.1 is vulnerable to unauthenticated remote code execution. Note that this vulnerability is caused by the incomplete patch of CVE-2023-37679.
Source: CSA/SingCERT, pwn.watch, 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 | ||
|---|---|---|---|
| nextgen | mirth_connect |
|
|
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 | Active Exploitation of Critical Vulnerability in NextGen Healthcare Mirth Connect (opens in a new tab)CSA/SingCERT | actively exploited | |
| Reference tagged as exploit | horizon3.ai (opens in a new tab) | PoC (publicly reported)reported, not verified | — |
| Packet Storm | Mirth Connect 4.4.0 Remote Command Execution (opens in a new tab)packetstormsecurity.com | PoC (publicly reported)reported, not verified | — |
References & sources
- horizon3.ainextgen-mirth-connect-remote-code-execution-vulnerability-cve-2…Exploit, Third-party advisory
- packetstormsecurity.comfiles/176920/Mirth-Connect-4.4.0-Remote-Command-Execution.htmlExploit, Third-party advisory, Vulnerability database
- cisa.govknown-exploited-vulnerabilities-catalog?field_cve=CVE-2023-43208government-resource, US government resource
- pwn.watchpwn.watch: NextGen Healthcare Mirth Connect Deserialization of Untrusted Datapwn-watch
- github.comNextGen Healthcare advisory: CVE-2023-43208pwn-watch
- NVD (NIST)NVD: CVE-2023-43208pwn-watch
- cisa.govCISA Known Exploited Vulnerabilities Catalogpwn-watch
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