1. Description Component "sdk/helper/ldaputil/client.go" — the shared LDAP utility library used by both the LDAP authentication backend and OpenLDAP secrets engine to construct LDAP search filters and bind DNs. Root Cause The LDAP utility contains a function selection error that causes incorrect escaping of user-controlled input in LDAP filter construction. Two lines construct the "bindDN" using "EscapeLDAPValue()": // Line 191 — UPN Domain path bindDN = fmt.Sprintf("%s@%s", EscapeLDAPValue(username), cfg.UPNDomain) // Line 193 — User DN path bindDN = fmt.Sprintf("%s=%s,%s", cfg.UserAttr, EscapeLDAPValue(username), cfg.UserDN) The problem: "EscapeLDAPValue()" implements RFC 4514 escaping, which is designed for Distinguished Name (DN) components. It only escapes characters meaningful in DNs: "+", ",", ";", """, "", "<", ">", and leading/trailing spaces. LDAP search filters (RFC 4515) have a different set of special characters: "", "(", ")", "", and NUL ("\x00"). None of these are escaped by "EscapeLDAPValue()". The correct function is "ldap.EscapeFilter()" from the "github.com/go-ldap/ldap/v3" package. The irony: the same file uses "ldap.EscapeFilter()" correctly at lines 225-226 in "RenderUserSearchFilter()" for the "UserFilter" template path, but the "GetUserDN()" function at lines 191-193 uses the wrong escape function. Exploitation Mechanics Username: alice)(objectClass= ↓ EscapeLDAPValue (no-op — no DN special chars) alice)(objectClass=* ↓ fmt.Sprintf("(&(objectClass=user)(sAMAccountName=%s))", escapedUsername) (&(objectClass=user)(sAMAccountName=alice)(objectClass=)) ^^ injection point The filter "(&(objectClass=user)(sAMAccountName=alice)(objectClass=))" is logically equivalent to: - "sAMAccountName=alice" AND "objectClass=user" AND "objectClass=" Since all entries match "objectClass=", the filter matches any user entry where "sAMAccountName" is "alice", effectively ignoring the "objectClass=user" constraint. By crafting more sophisticated injections (e.g., "alice)(|(sAMAccountName=admin"), the attacker can match arbitrary different user entries. Preconditions - LDAP authentication backend must be configured - Directory must be Active Directory (UPNDomain path) or use UserDN/UserAttr binding - Attacker controls the "username" field at login time 2. Proof of Concept Login with LDAP injection payload as username curl -k -X POST -H "Content-Type: application/json" -d '{ "username": "alice)(sAMAccountName=*", "password": "anything" }' https://localhost:8200/v1/auth/ldap/login/admin LDAP filter constructed: (&(objectClass=user)(sAMAccountName=alice)(sAMAccountName=*)) injection ──────────^ The filter matches the first user with objectClass=user If the LDAP server returns admin's entry first, the token is bound to the admin entity, inheriting all admin policies The LDAP search returns whichever entry the server ranks highest among results. In Active Directory with default sorting, this is often the oldest or alphabetically first user — potentially an administrative account. 3. Impact | Impact | Detail | |--------|--------| | Confidentiality | Token bound to a different LDAP user (e.g., admin) grants access to all secrets and policies belonging to that entity | | Integrity | Ability to modify secrets, write policies, or configure backends as the impersonated user | | Availability | Low direct impact, but administrative access enables disabling or misconfiguring the entire OpenBao instance | Likelihood: HIGH — the escape function mismatch is a well-documented antipattern in OWASP LDAP Injection guidance. The attack is trivially exploitable with no special tooling beyond "curl". Why This Is High Severity The LDAP auth backend is frequently used as a primary authentication method for enterprise OpenBao deployments. A successful LDAP injection against this backend can bypass the entire authentication chain, granting administrative access to the secrets store without needing to compromise an actual admin account. 4. Remediation Primary Fix: Use ldap.EscapeFilter Replace "EscapeLDAPValue" with "ldap.EscapeFilter" in both filter construction paths: import "github.com/go-ldap/ldap/v3" // Line 191 — UPN Domain path bindDN = fmt.Sprintf("%s@%s", ldap.EscapeFilter(username), cfg.UPNDomain) // Line 193 — User DN path bindDN = fmt.Sprintf("%s=%s,%s", cfg.UserAttr, ldap.EscapeFilter(username), cfg.UserDN) "EscapeLDAPValue" is still the correct choice for actual DN construction (where values are used as RDN components rather than filter values), but any value interpolated into an LDAP filter string must use "ldap.EscapeFilter". Audit: All Call Sites Review all usages of "EscapeLDAPValue" across the codebase to ensure none are used in filter context: grep -rn "EscapeLDAPValue" /root/cve-audit/openbao/ Defense-in-Depth - Apply the principle of least privilege to LDAP service accounts used by OpenBao - Use "UserFilter" with explicit attribute constraints to limit the search scope