CVE-2021-39031: IBM WebSphere Auth Bypass Vulnerability

CVE-2021-39031 Overview

CVE-2021-39031 is an LDAP injection vulnerability in IBM WebSphere Application Server Liberty versions 17.0.0.3 through 22.0.0.1. A remote authenticated attacker can send a specially crafted request to manipulate LDAP queries processed by the server. Successful exploitation grants the attacker access to unauthorized resources within the application. The flaw is tracked under IBM X-Force ID 213875 and is classified under [CWE-74] for improper neutralization of special elements in output used by a downstream component.

Critical Impact

Authenticated attackers can manipulate LDAP queries to bypass authorization controls and access restricted resources in WebSphere Liberty deployments.

Affected Products

• IBM WebSphere Application Server Liberty 17.0.0.3
• IBM WebSphere Application Server Liberty versions through 22.0.0.1
• Deployments relying on LDAP-based authentication or authorization within Liberty

Discovery Timeline

• 2022-01-25 - CVE-2021-39031 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-39031

Vulnerability Analysis

The vulnerability resides in how IBM WebSphere Application Server Liberty processes user-supplied input before incorporating it into Lightweight Directory Access Protocol (LDAP) queries. Input is not properly neutralized, allowing attacker-controlled characters to alter the structure of the resulting LDAP filter or distinguished name. The attacker must be authenticated, but no elevated privileges are required to exploit the flaw. Successful injection can cause the directory service to return entries the requester is not permitted to see, or to evaluate authorization decisions against attacker-influenced data.

Root Cause

The root cause is improper input neutralization, as reflected in [CWE-74]. Liberty constructs LDAP statements by concatenating user-controlled values without consistently escaping LDAP metacharacters such as *, (, ), \, and NUL bytes. When these characters reach the directory layer, they change the semantics of the query rather than being treated as literal data.

Attack Vector

The attack is delivered over the network through an authenticated session against the Liberty server. An attacker submits a crafted request whose parameter values contain LDAP filter syntax. Liberty embeds the values into a backend LDAP search, expanding the result set or altering authorization checks. The directory then returns objects or attributes that grant the attacker access to resources outside their authorized scope.

No verified public exploit code is available for this CVE. Refer to the IBM X-Force Vulnerability #213875 and IBM Support Node #6550488 entries for vendor technical details.

Detection Methods for CVE-2021-39031

Indicators of Compromise

• LDAP filter metacharacters such as *)(uid=, )(|, or \28\29 appearing in HTTP parameters submitted to Liberty endpoints
• Authenticated sessions issuing requests that result in access to resources outside the user's normal role scope
• Anomalous LDAP search filters or unusually broad result sets in directory server logs originating from the Liberty service account

Detection Strategies

• Inspect Liberty messages.log and trace.log for LDAP search operations containing unescaped wildcard or boolean operators in user-supplied fields
• Correlate authenticated HTTP requests against backend LDAP query patterns to identify input that survives into the filter string
• Apply web application firewall signatures targeting LDAP injection payloads on authenticated Liberty routes that perform directory lookups

Monitoring Recommendations

• Enable LDAP audit logging on the directory server and alert on filters that return abnormally large result sets from the Liberty bind account
• Monitor authorization decisions for sudden access to administrative or cross-tenant resources by standard user accounts
• Track Liberty version and fix-pack levels through configuration management to surface hosts still running 17.0.0.3 through 22.0.0.1

How to Mitigate CVE-2021-39031

Immediate Actions Required

• Apply the interim fix or upgrade to a Liberty release beyond 22.0.0.1 as documented in IBM Support Node #6550488
• Inventory all Liberty instances and identify those configured with LDAP user registries, which are the exploitable configurations
• Rotate credentials for the Liberty LDAP bind account if exploitation is suspected, and review authorization grants issued during the exposure window

Patch Information

IBM has issued remediation guidance through IBM Support Node #6550488. Administrators should apply the published interim fix or move to a fixed Liberty release. Vendor details are also tracked in IBM X-Force Vulnerability #213875.

Workarounds

• Restrict access to authenticated Liberty endpoints that perform LDAP lookups to trusted network segments until patches are applied
• Place a web application firewall in front of Liberty and block requests containing LDAP filter metacharacters in user-controlled fields
• Reduce the privileges of the Liberty LDAP bind account so that even a successful injection cannot enumerate or modify sensitive directory entries

# Configuration example
# Verify installed Liberty version before and after applying the fix
${WLP_HOME}/bin/productInfo version

# Apply IBM interim fix package (replace with the fix archive from IBM Support)
${WLP_HOME}/bin/installUtility install <fix-package>

# Restart the Liberty server to load patched binaries
${WLP_HOME}/bin/server stop <serverName>
${WLP_HOME}/bin/server start <serverName>