CVE-2019-14907 in Samba
Summary
by MITRE
All samba versions 4.9.x before 4.9.18, 4.10.x before 4.10.12 and 4.11.x before 4.11.5 have an issue where if it is set with "log level = 3" (or above) then the string obtained from the client, after a failed character conversion, is printed. Such strings can be provided during the NTLMSSP authentication exchange. In the Samba AD DC in particular, this may cause a long-lived process(such as the RPC server) to terminate. (In the file server case, the most likely target, smbd, operates as process-per-client and so a crash there is harmless).
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Analysis
by VulDB Data Team • 05/18/2025
This vulnerability exists in samba implementations across multiple version branches including 4.9.x before 4.9.18, 4.10.x before 4.10.12, and 4.11.x before 4.11.5. The issue manifests when samba is configured with log level set to 3 or higher, which enables verbose logging of authentication processes. During NTLMSSP authentication exchanges, samba processes client-provided strings that may contain invalid character encoding sequences. When character conversion fails, the system attempts to log these malformed strings, creating a potential exploitation vector. This flaw represents a classic case of improper error handling and insufficient input sanitization in network authentication services.
The technical implementation of this vulnerability stems from samba's logging mechanism when processing authentication requests in Active Directory Domain Controller configurations. When a client sends authentication data with invalid character encoding, the system fails to properly sanitize or escape the malformed string before logging it at verbose levels. The NTLMSSP protocol uses specific string formats and encoding conventions that when violated can cause unexpected behavior in the logging subsystem. The vulnerability specifically affects the RPC server process in AD DC environments where processes can remain long-lived, making them susceptible to termination due to malformed log output. The samba codebase does not adequately handle character encoding errors during authentication processing, leading to potential process crashes.
The operational impact of this vulnerability varies significantly based on the samba deployment type. In Active Directory Domain Controller environments, the RPC server process may terminate unexpectedly, causing service disruption and potential authentication failures for domain clients. This can lead to extended downtime and service degradation for critical domain services. However, in file server deployments using smbd processes, individual client connections may crash without affecting the overall server availability since smbd operates with one process per client. The vulnerability enables a denial-of-service condition that can be triggered by sending specifically crafted authentication requests with malformed character sequences. Attackers can exploit this by initiating authentication exchanges with invalid encoding data, causing the targeted samba processes to terminate.
Mitigation strategies for this vulnerability should focus on immediate version upgrades to patched samba releases, specifically 4.9.18, 4.10.12, and 4.11.5 or later. Organizations should also consider reducing log levels for authentication-related processes to avoid logging potentially malicious character sequences. Network segmentation and monitoring can help detect abnormal authentication patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-20: Improper Input Validation and CWE-704: Incorrect Type Conversion or Cast, both of which fall under the broader category of input validation failures. From an attack perspective, this vulnerability maps to ATT&CK technique T1550.003: Use of Valid Credentials with the potential to escalate to service disruption and denial-of-service conditions. Additionally, organizations should implement proper log sanitization procedures to prevent malicious strings from being logged in verbose modes, ensuring that character encoding errors do not propagate into system stability issues.