CVE-2021-42127

What it actually does

CVE-2021-42127 is an unauthenticated remote code execution vulnerability caused by deserialization of untrusted data in Ivanti Avalanche versions before 6.3.3. The vulnerable Data Repository Service, reachable through the Inforail Service, can process attacker-controlled serialized input and instantiate unsafe objects. Because exploitation requires no credentials, no user interaction, and low complexity, a remote attacker who can reach the affected service can execute arbitrary code in the context of the Avalanche service process, potentially gaining full control of the Avalanche server and its managed-device infrastructure.

Why it matters to the business

Successful exploitation can allow an attacker to take over the Ivanti Avalanche server, disrupt mobile-device and warehouse-device management operations, steal configuration data or credentials accessible to the service, deploy malicious changes to managed devices, or use the server as a foothold for broader network compromise. Although this vulnerability is not currently listed in CISA KEV and public exploit maturity is reported as none, the CVSS score is critical and the EPSS score is high, meaning exposed systems should be treated as urgent remediation priorities, especially where Avalanche services are reachable from untrusted networks.

How an attack unfolds

An attacker first identifies an Ivanti Avalanche deployment exposing the vulnerable Data Repository or Inforail service. They then connect to the service over the network and send a crafted serialized payload designed to trigger unsafe deserialization. The service processes the untrusted object data before proper validation, causing attacker-controlled code paths to execute inside the Avalanche service process. Once code execution is achieved, the attacker may run operating-system commands, create persistence, dump credentials or configuration files, stage additional tools, pivot to adjacent systems, or manipulate Avalanche management functions to affect enrolled devices.

How to fix it

Upgrade Ivanti Avalanche to version 6.3.3 or later, which addresses the vulnerable deserialization behavior. If immediate upgrade is not possible, restrict network access to Avalanche Data Repository and Inforail services to trusted management hosts only, block exposure from the internet and untrusted segments, apply host firewall rules, and place the service behind VPN or administrative access controls. Run the Avalanche services with least-privilege service accounts where supported, review stored credentials and integration secrets after remediation, and monitor the server for signs of prior compromise before returning it to normal operation.

How to confirm the fix worked

Confirm the installed Ivanti Avalanche version is 6.3.3 or later on every Avalanche server. Validate that Data Repository Service and Inforail Service ports are not reachable from the internet or untrusted network segments. Use authenticated asset inventory, vendor management consoles, service binaries, package metadata, or administrative UI version reporting to verify patch status. Perform a controlled network scan from untrusted segments to ensure the service is not exposed. After patching, restart affected services if required and confirm normal Avalanche functionality while monitoring logs for deserialization errors, service crashes, or unexpected child processes.

Typical attack path

1. Scan for reachable Ivanti Avalanche services, especially Data Repository Service or Inforail Service endpoints exposed beyond trusted management networks.
2. Fingerprint the service version or behavior to determine whether it is older than Ivanti Avalanche 6.3.3.
3. Send a crafted serialized object payload to the vulnerable service without authenticating.
4. Achieve code execution under the Avalanche service account or process context.
5. Execute discovery commands to identify privileges, local configuration, credentials, and network reachability.
6. Deploy follow-on tooling, persistence, or lateral movement mechanisms if the server has access to internal systems.
7. Optionally disrupt Avalanche operations or use device-management capabilities to impact managed endpoints.

How to detect it

To determine whether exploitation already occurred, review Ivanti Avalanche application and service logs, Windows Event Logs, EDR telemetry, firewall logs, proxy logs, and network flow data for inbound connections to Data Repository Service or Inforail Service from unusual or untrusted sources. Look for deserialization-related Java or application exceptions followed by service crashes, restarts, or unexpected operating-system command execution. On Windows hosts, investigate Avalanche-related service processes spawning cmd.exe, powershell.exe, wscript.exe, cscript.exe, rundll32.exe, regsvr32.exe, certutil.exe, bitsadmin.exe, mshta.exe, or other tools not normally launched by the product. Review file creation in temporary directories, Avalanche installation directories, startup locations, scheduled tasks, new services, and recently modified scripts or binaries. Network telemetry should be searched for serialized Java object headers or abnormal payloads sent to Avalanche service ports. Because attacker payloads vary, absence of a fixed IOC does not prove safety; correlate suspicious service access, errors, child-process execution, and post-exploitation behavior.

• Data Repository Service
• Inforail Service
• java.io.ObjectInputStream
• java.io.InvalidClassException
• java.io.StreamCorruptedException
• java.lang.ClassNotFoundException
• java.lang.reflect.InvocationTargetException
• AC ED 00 05
• \xAC\xED\x00\x05
• cmd.exe /c
• powershell.exe -
• powershell.exe -enc
• certutil.exe -urlcache
• bitsadmin /transfer
• wscript.exe
• cscript.exe
• mshta.exe
• rundll32.exe
• regsvr32.exe
• schtasks /create
• New-Service
• sc create

What your security team should do

• Patch all Ivanti Avalanche servers to version 6.3.3 or later as a high-priority action due to critical remote-code-execution impact and elevated EPSS probability.
• Immediately remove public or broad network exposure to Avalanche Data Repository and Inforail services; allow access only from trusted administrative and management networks.
• Hunt for evidence of exploitation before and after patching, focusing on suspicious child processes spawned by Avalanche services and deserialization-related exceptions.
• Review Avalanche server privileges, service account permissions, stored credentials, and integration secrets; rotate credentials if compromise cannot be ruled out.
• Add EDR and SIEM detections for command interpreters, scripting engines, download utilities, or archive tools launched from Avalanche service processes.
• Ensure Avalanche servers are included in vulnerability management, external attack-surface monitoring, backup, and incident-response playbooks.
• If suspicious activity is found, isolate the server, preserve logs and forensic artifacts, and investigate lateral movement from the Avalanche host.