CVE-2025-14017: libcurl Race Condition Vulnerability

CVE-2025-14017 Overview

CVE-2025-14017 is a thread safety vulnerability in libcurl affecting multi-threaded LDAPS (LDAP over TLS) transfers. When changing TLS options in one thread, the modifications would inadvertently apply globally, potentially affecting other concurrently running transfers. This flaw could lead to unintentional disabling of certificate verification across multiple threads, creating security gaps in applications that rely on libcurl for secure LDAP communications.

Critical Impact

Disabling certificate verification for a specific transfer could unintentionally disable the feature for other threads, potentially exposing sensitive LDAP communications to man-in-the-middle attacks.

Affected Products

• libcurl (LDAPS functionality)
• Applications using libcurl for multi-threaded LDAPS transfers
• Systems with concurrent TLS-secured LDAP connections

Discovery Timeline

• 2026-01-07 - Vulnerability disclosed via Openwall OSS Security Discussion
• 2026-01-08 - CVE CVE-2025-14017 published to NVD
• 2026-01-08 - Last updated in NVD database

Technical Details for CVE-2025-14017

Vulnerability Analysis

This vulnerability stems from improper thread isolation when handling TLS configuration options during LDAPS transfers in libcurl. In multi-threaded applications, each thread should maintain its own independent TLS configuration state. However, due to the nature of this flaw, TLS option changes made by one thread propagate to a global context, affecting all concurrent transfers.

The most significant security implication is that if one thread legitimately disables certificate verification (perhaps for a specific internal service that uses a self-signed certificate), this configuration could inadvertently apply to other threads that require strict certificate validation. This creates a window of opportunity for attackers to perform man-in-the-middle attacks on connections that were intended to be securely validated.

Root Cause

The root cause is a race condition combined with improper thread-local storage management for TLS options in libcurl's LDAPS implementation. The TLS configuration state was inadvertently shared across threads rather than being maintained in a thread-local or transfer-specific context. This architectural flaw allows concurrent threads to interfere with each other's security configurations.

Attack Vector

An attacker could exploit this vulnerability in scenarios where:

1. A multi-threaded application uses libcurl for LDAPS transfers
2. One thread modifies TLS options (such as disabling certificate verification)
3. Other threads performing concurrent LDAPS transfers inherit the weakened TLS configuration
4. The attacker positions themselves to intercept traffic from threads that should have had certificate verification enabled

The vulnerability could be exploited in a man-in-the-middle position to intercept LDAP credentials, directory queries, or modify LDAP responses when certificate verification is unintentionally disabled.

Detection Methods for CVE-2025-14017

Indicators of Compromise

• Unexpected TLS certificate validation failures or successes in LDAPS connections
• Anomalous LDAP traffic patterns suggesting potential interception
• Application logs showing inconsistent TLS configuration behavior across threads
• Network traffic analysis revealing unverified TLS handshakes for connections that should require validation

Detection Strategies

• Monitor libcurl version in use across infrastructure and flag vulnerable versions
• Implement network monitoring for LDAPS connections that accept untrusted certificates
• Review application logs for thread-related TLS configuration warnings
• Deploy TLS inspection tools to verify certificate validation is occurring as expected

Monitoring Recommendations

• Enable verbose logging for libcurl TLS operations in multi-threaded applications
• Implement certificate pinning monitoring to detect unexpected certificate changes
• Set up alerts for LDAP authentication anomalies that could indicate credential interception
• Monitor network traffic for signs of man-in-the-middle activity on LDAP ports (389, 636)

How to Mitigate CVE-2025-14017

Immediate Actions Required

• Review all applications using libcurl for multi-threaded LDAPS transfers
• Ensure certificate verification is explicitly enabled for all critical LDAPS connections
• Avoid changing TLS options dynamically in multi-threaded environments until patched
• Consider implementing application-level certificate validation as an additional safeguard
• Update libcurl to the latest patched version when available

Patch Information

Consult the cURL CVE-2025-14017 Advisory for official patch information and updated versions. The advisory provides detailed guidance on affected versions and remediation steps. Additional technical details are available in the cURL CVE-2025-14017 JSON Data format for automated processing.

Workarounds

• Avoid using multi-threaded LDAPS transfers with shared libcurl handles until a patch is applied
• Implement process-level isolation instead of thread-level parallelism for LDAPS operations
• Use separate curl easy handles per thread and avoid concurrent TLS option modifications
• Deploy network-level controls to ensure LDAPS traffic is protected regardless of application-level certificate validation
• Consider using alternative LDAP libraries that provide proper thread isolation for critical applications