CVE-2026-39962 Overview
CVE-2026-39962 is an LDAP injection vulnerability affecting MISP (Malware Information Sharing Platform), an open source threat intelligence and sharing platform. Prior to version 2.5.36, the ApacheAuthenticate.php component fails to properly neutralize special elements in LDAP queries, allowing attackers to inject malicious LDAP query fragments via an unsanitized username value. This vulnerability specifically manifests when ApacheAuthenticate.apacheEnv is configured to use a user-controlled server variable instead of the default REMOTE_USER, such as in certain reverse proxy configurations.
Critical Impact
An attacker who can control the username value can manipulate the LDAP search filter, potentially bypassing authentication constraints or executing unauthorized LDAP queries against the directory server, compromising the integrity of threat intelligence sharing operations.
Affected Products
- MISP versions prior to 2.5.36
- MISP installations using ApacheAuthenticate with custom server variable configurations
- MISP deployments behind reverse proxies with non-standard authentication header mapping
Discovery Timeline
- 2026-04-09 - CVE CVE-2026-39962 published to NVD
- 2026-04-09 - Last updated in NVD database
Technical Details for CVE-2026-39962
Vulnerability Analysis
This vulnerability falls under CWE-90 (Improper Neutralization of Special Elements used in an LDAP Query), commonly known as LDAP Injection. The flaw exists in the ApacheAuthenticate.php authentication module within MISP, which handles Apache-based authentication integration.
When MISP administrators configure the apacheEnv setting to read the authenticated username from a server variable other than REMOTE_USER, the application becomes vulnerable. In certain proxy architectures, the username value may be sourced from HTTP headers or other user-controllable inputs. The vulnerable code path constructs LDAP search filters using this username value without proper sanitization or escaping of LDAP special characters.
An attacker exploiting this vulnerability could craft malicious username inputs containing LDAP metacharacters such as *, (, ), \, and NUL bytes to modify the structure of LDAP queries. This could enable authentication bypass by manipulating filter logic to return unauthorized user entries, or allow information disclosure by constructing queries that extract sensitive directory attributes.
Root Cause
The root cause is insufficient input validation and improper neutralization of LDAP special characters in the username parameter before constructing LDAP search filters. The ApacheAuthenticate.php module directly incorporates user-supplied data into LDAP query strings without applying proper escaping functions or parameterized query mechanisms. This allows LDAP metacharacters in the username to alter the semantic meaning of the constructed filter expression.
Attack Vector
The attack is network-based and requires specific environmental conditions. The attacker must be able to control the server variable that MISP reads as the authenticated username. This typically occurs in reverse proxy deployments where:
- The reverse proxy forwards authentication information via custom HTTP headers
- MISP is configured to read the username from a header like HTTP_X_AUTHENTICATED_USER instead of the secure REMOTE_USER variable
- The upstream proxy does not properly sanitize or validate the forwarded header values
An attacker can then inject LDAP filter manipulation payloads through the controllable header. For example, injecting a username like admin)(|(objectClass=* could transform a simple equality filter into a wildcard match that returns all directory entries, potentially bypassing authentication checks entirely.
The vulnerability requires some level of user interaction or environmental misconfiguration to be exploitable, but no prior authentication is needed to attempt exploitation.
Detection Methods for CVE-2026-39962
Indicators of Compromise
- Unusual authentication events with usernames containing LDAP special characters such as *, (, ), \, or |
- LDAP server logs showing malformed or anomalous search filter syntax
- Authentication successes for accounts that should not have access or do not match expected user patterns
- Increased LDAP query volume or queries returning unexpectedly large result sets
Detection Strategies
- Deploy Web Application Firewall (WAF) rules to detect and block LDAP injection patterns in authentication headers
- Monitor Apache access logs for requests containing LDAP metacharacters in authentication-related headers
- Implement LDAP server query logging and establish baselines to detect anomalous filter constructions
- Configure SentinelOne Singularity to monitor for suspicious authentication patterns and LDAP query anomalies
Monitoring Recommendations
- Enable verbose logging for LDAP authentication events in MISP and correlate with directory server logs
- Set up alerts for authentication attempts with special characters that are not typically present in valid usernames
- Monitor for multiple failed authentication attempts followed by successful authentications from the same source
- Review reverse proxy configurations to ensure proper validation and sanitization of forwarded authentication headers
How to Mitigate CVE-2026-39962
Immediate Actions Required
- Upgrade MISP to version 2.5.36 or later immediately to apply the security fix
- Review current ApacheAuthenticate.apacheEnv configuration and assess whether user-controlled variables are in use
- If upgrade is not immediately possible, switch to using the default REMOTE_USER variable for authentication
- Audit reverse proxy configurations to ensure authentication headers cannot be spoofed by end users
Patch Information
The vulnerability has been addressed in MISP version 2.5.36. The fix involves proper sanitization of username inputs before constructing LDAP queries. The relevant security patches can be found in the following commits:
The official release containing the fix is available at GitHub MISP Release v2.5.36. For additional details, consult the GitHub Security Advisory GHSA-mc53-48w8-9g63.
Workarounds
- Configure ApacheAuthenticate.apacheEnv to use REMOTE_USER rather than custom user-controllable server variables
- Implement strict input validation at the reverse proxy layer to reject authentication headers containing LDAP special characters
- Deploy network-level access controls to restrict LDAP server access to only trusted MISP application servers
- Consider temporarily disabling Apache-based authentication and switching to alternative authentication mechanisms until the patch can be applied
# Configuration example - Verify and restrict apacheEnv setting
# In MISP config.php, ensure apacheEnv uses REMOTE_USER
# Check current configuration
grep -r "apacheEnv" /var/www/MISP/app/Config/
# Update to secure configuration if custom variable is in use
# Set ApacheAuthenticate.apacheEnv to REMOTE_USER
sudo -u www-data /var/www/MISP/app/Console/cake Admin setSetting "ApacheAuthenticate.apacheEnv" "REMOTE_USER"
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
