CVE-2026-4256: LDAP Injection in PEAKUP PassGate – Critical Authentication Risk

Technical summary

CVE-2026-4256 is an LDAP injection flaw (CWE-90) in PassGate stemming from improper neutralization of special characters in LDAP query construction. The vulnerability allows unauthenticated, network-accessible exploitation. With a CVSS 3.1 score of 8.2 (HIGH), the attack vector is network-based, complexity is low, and no privileges or user interaction are required. The impact includes high confidentiality loss (unauthorized directory access) and low integrity impact (limited query modification). Availability is not directly affected.

Business impact

Exploitation could lead to unauthorized access to directory information stored in LDAP backends, such as user credentials, email addresses, organizational structure, and other sensitive attributes. An attacker could potentially enumerate valid accounts, extract password hashes if stored in LDAP, or modify directory entries depending on PassGate's LDAP permissions model. Organizations relying on PassGate for authentication or directory integration face authentication bypass risks and data exfiltration exposure.

Affected systems

PassGate versions through 30042026 are affected. Consult the vendor advisory to confirm your deployed version and whether your installation uses LDAP as a backend authentication or directory service. The vulnerability is exploitable only if PassGate is exposed to network access and configured to process LDAP queries.

Exploitability

The vulnerability is highly exploitable. No authentication is required, the attack complexity is low, and the flaw can be triggered remotely over standard network connections. An attacker needs only to craft malicious LDAP query syntax in input fields processed by PassGate—a technique well-understood by security researchers and increasingly automated in attack frameworks. The lack of KEV listing does not diminish the practical exploitability; it reflects that active exploitation has not yet been formally documented in public databases at the time of publication.

Remediation

Patch PassGate immediately to a version released after 30042026 per the vendor advisory. Until patching is possible, apply input validation and output encoding to LDAP queries, implement Web Application Firewall rules to block LDAP injection patterns, restrict network access to PassGate to trusted sources only, and consider using prepared statements or parameterized LDAP queries if the product supports them. Validate your remediation with security testing before returning systems to production.

Patch guidance

Contact PEAKUP Technology Inc. or check their official support portal for patches addressing CVE-2026-4256. Patches should be tested in a non-production environment first to verify compatibility with your authentication workflows and any dependent systems. Once validated, deploy patches to all affected instances in a controlled manner. Document the patch version applied and the date of deployment for compliance and incident response records.

Detection guidance

Monitor PassGate logs for unusual LDAP query patterns, including wildcard characters (*), logical operators (|, &, !), parentheses, or escaped sequences in authentication fields or search inputs. Network intrusion detection signatures may identify LDAP injection payloads. Conduct regular vulnerability scanning against PassGate instances to identify unpatched versions. Review LDAP access logs for unauthorized directory queries or failed authentication attempts with malformed syntax.

Why prioritize this

This vulnerability merits immediate attention due to its high CVSS score (8.2), unauthenticated network exploitability, and direct impact on authentication and directory confidentiality. The lack of user interaction required and the common reliance on LDAP in enterprise environments amplify risk. Organizations using PassGate should treat this as a critical patch priority.

Risk score, explained

The CVSS 3.1 score of 8.2 reflects the combination of network accessibility (AV:N), low attack complexity (AC:L), no authentication requirement (PR:N), no user interaction (UI:N), and significant confidentiality impact (C:H) against LDAP directory data. The low integrity impact (I:L) and no availability impact (A:N) prevent a critical score, but the ease of exploitation and sensitive nature of directory information justify the HIGH severity rating.

Frequently asked questions