CVE-2026-103878 in LDAP API
Summary
by MITRE • 10/02/2026
Cleartext transmission of sensitive information vulnerability in Apache Directory LDAP API.
A StartTLS extended operation started after a Search request has been sent can lead to receive data in plain text before the TLS Handshake has been completed.
This issue affects Apache Directory LDAP API: from 2.1.0 before 2.1.9.
Users are recommended to upgrade to version 2.1.9, which fixes the issue.
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Analysis
by VulDB Data Team • 10/02/2026
The vulnerability identified in the Apache Directory LDAP API represents a critical flaw in how secure channel establishment is handled during an active session. Specifically, this issue arises when a client initiates a StartTLS extended operation immediately following a Search request that has already been transmitted to the server. In standard Lightweight Directory Access Protocol operations, data exchanged prior to the completion of Transport Layer Security handshake procedures remains unencrypted and visible in cleartext on the network wire. This behavior contradicts fundamental security expectations for directory services which often handle highly sensitive authentication credentials, user attributes, and organizational structures that require confidentiality during transit.
The technical root cause lies in the sequencing logic within the LDAP API implementation versions ranging from 2.1.0 up to but not including 2.1.9. When a Search request is sent, it may trigger responses or intermediate data flows before the StartTLS negotiation fully encrypts the subsequent communication channel. If the application layer does strictly enforce encryption for all traffic after authentication begins, this gap allows an attacker positioned in the network path to intercept and read sensitive information that was transmitted during this window of vulnerability. The flaw essentially creates a blind spot where security controls are temporarily bypassed due to improper state management between protocol operations.
From an operational impact perspective, this cleartext transmission exposes organizations using affected versions of Apache Directory LDAP API to significant risks including credential theft, unauthorized data access, and potential compromise of directory integrity. Attackers performing man-in-the-middle attacks can exploit this window to capture usernames, passwords, or other personally identifiable information contained within search results or associated metadata. This aligns with CWE-319 which classifies cleartext transmission of sensitive information as a distinct weakness category. The failure to ensure encryption for all relevant data flows constitutes a severe breach of confidentiality requirements mandated by most regulatory frameworks and security best practices.
This vulnerability also maps directly to MITRE ATT&CK technique T1557, specifically Adversary-in-the-Middle or Lateral Tool Transfer variants that rely on network sniffing to harvest credentials and sensitive data. By exploiting this timing flaw, adversaries can establish a passive listening position without needing to break encryption algorithms, simply by capturing the unencrypted packets sent before the TLS handshake completes. The persistence of such vulnerabilities in widely used directory APIs underscores the importance of rigorous protocol state validation during security context transitions.
To mitigate this risk, organizations must upgrade their Apache Directory LDAP API dependencies to version 2.1.9 or later where the issue has been resolved. Developers should verify that all library references are updated across application codebases and build configurations. Additionally, implementing defense-in-depth strategies such as strict certificate pinning and monitoring for anomalous network traffic patterns can provide supplementary protection against exploitation attempts while migration efforts proceed. Regular security audits of directory service implementations remain essential to ensure compliance with modern encryption standards and prevent similar timing-based vulnerabilities in future deployments.