CVE-2018-5709 in Kerberos 5
Summary
by MITRE
An issue was discovered in MIT Kerberos 5 (aka krb5) through 1.16. There is a variable "dbentry->n_key_data" in kadmin/dbutil/dump.c that can store 16-bit data but unknowingly the developer has assigned a "u4" variable to it, which is for 32-bit data. An attacker can use this vulnerability to affect other artifacts of the database as we know that a Kerberos database dump file contains trusted data.
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Analysis
by VulDB Data Team • 12/29/2019
The vulnerability described in CVE-2018-5709 represents a critical integer overflow flaw within the MIT Kerberos 5 implementation that affects versions through 1.16. This issue manifests in the kadmin/dbutil/dump.c component where a 16-bit variable named "dbentry->n_key_data" is improperly assigned a 32-bit unsigned integer value from a u4 variable. The mismatch between these data types creates a condition where the 32-bit value can exceed the maximum representable value of the 16-bit container, leading to unexpected behavior during database dump operations. This type of vulnerability falls under the CWE-190 category of Integer Overflow or Wraparound, which is classified as a serious weakness in software security.
The technical exploitation of this vulnerability occurs during Kerberos database dump operations where the system processes key data entries from the authentication database. When an attacker can manipulate or control the input data that populates the n_key_data field, they can cause the 16-bit variable to overflow, potentially corrupting adjacent memory locations or causing the application to behave unpredictably. This flaw is particularly dangerous because it affects the kadmin/dbutil/dump.c module, which is responsible for creating backup copies of the Kerberos database that contains highly sensitive authentication information including principal keys and access credentials. The database dump files generated by this vulnerable code contain trusted data that is essential for Kerberos authentication services, making any corruption or manipulation of these files a significant security risk.
The operational impact of CVE-2018-5709 extends beyond simple data corruption, as it can enable attackers to manipulate the Kerberos database in ways that compromise the entire authentication infrastructure. Since the database dump functionality is used for backup and recovery operations, an attacker who successfully exploits this vulnerability could potentially create malformed dump files that, when processed by other Kerberos components, could lead to denial of service conditions or even privilege escalation. The vulnerability's severity is amplified by the fact that Kerberos is widely used in enterprise environments for single sign-on and secure authentication, meaning that a successful exploitation could affect thousands of users and systems. This flaw aligns with ATT&CK technique T1552.001 for Unsecured Credentials and T1068 for Exploitation for Privilege Escalation, as it provides a potential pathway for attackers to gain unauthorized access to privileged authentication data.
Mitigation strategies for CVE-2018-5709 should focus on immediate patching of affected MIT Kerberos installations to version 1.16.1 or later, which contains the necessary fix for the integer type mismatch. Organizations should also implement monitoring of database dump operations to detect any unusual behavior or malformed output that might indicate exploitation attempts. Security teams should conduct thorough assessments of their Kerberos infrastructure to identify any systems running vulnerable versions and ensure proper access controls are in place for database dump operations. Additionally, implementing network segmentation and privilege separation for Kerberos administration functions can limit the potential impact if exploitation occurs. The fix implemented in the patched versions addresses the root cause by ensuring proper type alignment between the 16-bit n_key_data variable and its 32-bit source, preventing the overflow condition that enabled the vulnerability.