Описание
OpenBao: LDAPi ldaputil (wrong escape func)
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():
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
The filter (&(objectClass=user)(sAMAccountName=alice)(objectClass=*)) is logically equivalent to:
sAMAccountName=aliceANDobjectClass=userANDobjectClass=*
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
usernamefield at login time
2. Proof of Concept
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:
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:
Defense-in-Depth
- Apply the principle of least privilege to LDAP service accounts used by OpenBao
- Use
UserFilterwith explicit attribute constraints to limit the search scope
Пакеты
github.com/openbao/openbao
>= 0.1.0, <= 2.5.4
Отсутствует
github.com/openbao/openbao
< 0.0.0-20260617104213-10b7825c714c
0.0.0-20260617104213-10b7825c714c
Связанные уязвимости
OpenBao is an open source identity-based secrets management system. Prior to 2.5.5, OpenBao used EscapeLDAPValue, an RFC 4514 distinguished-name escaping function, where RFC 4515 LDAP search-filter escaping was required in sdk/helper/ldaputil/client.go GetUserDN. With the LDAP authentication backend configured for an Active Directory UPNDomain path or UserDN and UserAttr binding, an attacker-controlled username containing filter metacharacters could alter the search predicate and select a different directory entry because EscapeLDAPValue does not neutralize the characters handled by ldap.EscapeFilter. A resulting token could be associated with another LDAP identity and gain access to secrets, policies, or modification capabilities assigned to that identity. This issue is fixed in version 2.5.5.
OpenBao is an open source identity-based secrets management system. Pr ...
