BaseFortify

Executive Summary

The vulnerability in CVE-2026-11789 affects the 389 Directory Server's SMD5 password storage plugin. It arises from an integer underflow when calculating the salt length from a crafted password hash that is shorter than 16 bytes. This underflow causes the salt length to wrap around to a very large number, leading to a buffer over-read.

Specifically, the plugin subtracts the fixed MD5 hash length (16 bytes) from the decoded hash length using unsigned 32-bit arithmetic. If the decoded hash length is less than 16 bytes, the subtraction underflows, resulting in a large incorrect salt length. When the system attempts to process this, it reads beyond the intended buffer, causing the LDAP server process (ns-slapd) to crash with a segmentation fault (SIGSEGV).

An attacker with Directory Manager privileges can exploit this by planting a maliciously crafted SMD5 hash. Any subsequent authentication attempt (BIND operation) triggers the crash, causing a denial of service.

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Impact Analysis

This vulnerability can cause the 389 Directory Server to crash during authentication attempts, resulting in a denial of service (DoS).

An attacker with Directory Manager privileges can exploit this flaw by inserting a specially crafted SMD5 password hash. This causes the LDAP server to crash whenever a user attempts to authenticate, potentially disrupting services that rely on the directory server for authentication and authorization.

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Detection Guidance

This vulnerability causes the ns-slapd process of the 389 Directory Server to crash with a SIGSEGV signal during authentication when a maliciously crafted SMD5 password hash shorter than 16 bytes is used.

To detect this vulnerability on your system, monitor the ns-slapd process for unexpected crashes or segmentation faults, especially during LDAP BIND operations.

You can check system logs (e.g., /var/log/messages, /var/log/syslog, or journalctl) for crash reports related to ns-slapd.

Additionally, you can use commands like:

• journalctl -u ns-slapd.service --since "1 hour ago" | grep -i segfault
• grep -i ns-slapd /var/log/messages | grep -i crash
• ps aux | grep ns-slapd (to check if the process is running)
• Use LDAP client tools to perform BIND operations and observe if the server crashes, indicating exploitation attempts.

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Mitigation Strategies

Immediate mitigation steps include:

• Restrict Directory Manager privileges to trusted administrators only, as exploitation requires these privileges.
• Monitor and audit password hashes stored in the 389 Directory Server to detect and remove any SMD5 hashes shorter than 16 bytes.
• Avoid accepting or processing authentication requests with suspicious or malformed SMD5 password hashes.
• Apply any available patches or updates from your vendor addressing this vulnerability as soon as they are released.
• Consider temporarily disabling the SMD5 password storage plugin if feasible until a patch is applied.

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Compliance Impact

The provided information does not specify any direct impact of this vulnerability on compliance with common standards and regulations such as GDPR or HIPAA.

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