CVE-2023-28126

What it actually does

CVE-2023-28126 is an authentication bypass in Ivanti Avalanche 6.3.x and earlier. The flaw involves improper handling of authentication state through the SetUser method and a race condition in the authentication message flow. A remote, unauthenticated attacker may be able to manipulate or win the authentication sequence to obtain access without valid credentials. The CVSS vector indicates network reachability, no required privileges, no user interaction, high attack complexity, and high confidentiality impact, with no direct integrity or availability impact scored.

Why it matters to the business

Successful exploitation can allow an attacker to access Avalanche management functionality or sensitive management data without logging in legitimately. Because Avalanche is used to manage mobile and rugged devices, exposed information may include device inventory, users, configuration profiles, deployment details, connectivity settings, or other operational data useful for follow-on attacks. Although this CVE is not listed in CISA KEV and is not known to be ransomware-associated, the EPSS score is elevated, so internet-exposed or broadly reachable Avalanche deployments should be treated as higher-priority remediation targets.

How an attack unfolds

An attacker first identifies a reachable Ivanti Avalanche instance running version 6.3.x or earlier. They then interact with the authentication workflow and attempt to abuse the SetUser method or trigger the race condition in the authentication message exchange. If the timing and request sequence succeed, the application may establish or accept an authenticated context even though the attacker did not provide valid credentials. The attacker can then access data or functions available to the resulting session. Because the attack has high complexity, exploitation may require repeated attempts, precise timing, or automation, but it does not require prior authentication or user interaction.

How to fix it

Upgrade Ivanti Avalanche to a vendor-supported fixed release newer than the affected 6.3.x line. If exact package-level fixed versions are not available in internal asset data, use Ivanti’s current advisory and release notes to identify the appropriate fixed version, and preferentially deploy the latest supported Avalanche release. Where immediate upgrade is not possible, restrict network access to Avalanche management interfaces, require VPN or administrative network access, block direct internet exposure, enforce strong administrative authentication controls, and monitor authentication activity closely. Segregate the Avalanche server from general user networks and limit access to trusted management hosts only.

How to confirm the fix worked

Confirm that all Ivanti Avalanche installations are inventoried and that no instance reports version 6.3.x or earlier. Validate the upgrade through the application UI, installed package metadata, service binaries, or vendor-supported version commands. Confirm that Avalanche management interfaces are not directly exposed to untrusted networks unless explicitly required and protected. Review access controls to ensure only trusted administrative sources can reach the service. After remediation, perform an authenticated and unauthenticated access test to verify that authentication bypass is no longer possible and that direct unauthenticated access to management functions is denied.

Typical attack path

1. Identify an exposed Ivanti Avalanche service or management interface.
2. Fingerprint the deployment to determine whether it is running Avalanche 6.3.x or earlier.
3. Send crafted authentication-related requests targeting the SetUser method or authentication message flow.
4. Repeat or time requests to exploit the race condition in authentication handling.
5. Obtain an authenticated session or access context without valid credentials.
6. Enumerate accessible management data, device inventory, configuration details, or other sensitive information.
7. Use harvested information to support lateral movement, credential attacks, device targeting, or additional compromise paths.

How to detect it

To determine whether exploitation may have already occurred, review Avalanche application logs, web or service access logs, reverse proxy logs, Windows Event Logs, EDR telemetry, and network flow records for authentication anomalies. Focus on repeated unauthenticated requests to authentication-related endpoints, unusual references to SetUser, high-frequency login/session attempts, successful sessions without preceding valid login events, and administrative access from unfamiliar IP addresses or non-administrative networks. Because exploitation involves a race condition, look for bursts of closely timed authentication messages from the same source, especially followed by successful access. Correlate Avalanche session creation events with identity-provider, LDAP, Windows, or local authentication logs to identify sessions that do not map to a legitimate credential validation event. Also review for subsequent enumeration of device inventory, profile exports, configuration downloads, or unusual management actions. There are no widely established public file, process, or network IOCs specific to this CVE, so detection should emphasize behavioral evidence and authentication-flow inconsistencies.

• SetUser
• authentication message
• Avalanche
• Wavelink Avalanche
• Ivanti Avalanche

What your security team should do

• Prioritize remediation for any Avalanche instance reachable from the internet, partner networks, remote-access networks, or broadly accessible internal segments.
• Upgrade Avalanche to a vendor-supported fixed version newer than 6.3.x, preferably the latest supported release.
• If upgrade cannot be completed immediately, restrict access to Avalanche management services using firewall rules, VPN requirements, jump hosts, or administrative network segmentation.
• Review Avalanche authentication and access logs for unusual unauthenticated requests, repeated login/session attempts, or SetUser-related activity.
• Hunt for unexpected administrative sessions, unknown source IP addresses, abnormal access times, and access from non-administrative networks.
• Rotate credentials or secrets stored in or managed by Avalanche if there is evidence of unauthorized access.
• Ensure Avalanche servers are included in vulnerability scanning, configuration monitoring, EDR coverage, centralized logging, and backup routines.
• Document compensating controls and set an explicit remediation deadline, given the elevated EPSS score despite absence from KEV.