CVE-2002-0036 in Kerberos
Summary
by MITRE
Integer signedness error in MIT Kerberos V5 ASN.1 decoder before krb5 1.2.5 allows remote attackers to cause a denial of service via a large unsigned data element length, which is later used as a negative value.
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Analysis
by VulDB Data Team • 08/25/2025
The vulnerability described in CVE-2002-0036 represents a critical integer signedness error within the ASN.1 decoder component of MIT Kerberos V5 versions prior to 1.2.5. This flaw exists at the core of the authentication system that millions of organizations rely upon for secure network communications. The issue manifests when the system processes large unsigned data element lengths that are subsequently interpreted as signed integers, creating a scenario where valid unsigned values become negative when cast to signed representations. This fundamental error in data type handling creates a pathway for remote attackers to exploit the authentication infrastructure through carefully crafted malicious data packets.
The technical implementation of this vulnerability occurs within the ASN.1 decoding logic where the system fails to properly validate or convert unsigned length indicators before using them in arithmetic operations or memory allocation calculations. When an unsigned data element length exceeds the maximum value that can be represented by a signed integer type, the conversion results in a negative value that disrupts normal program execution. This specific condition falls under CWE-191, which describes integer underflow and overflow errors, and more specifically CWE-194, which addresses signed to unsigned conversion errors. The flaw demonstrates a classic example of improper handling of data type conversions that can lead to unpredictable behavior in cryptographic systems.
From an operational perspective, this vulnerability creates a significant denial of service condition that can effectively disable Kerberos authentication services without requiring authentication credentials or advanced attack capabilities. Attackers can simply send specially crafted ASN.1 encoded packets with large unsigned length values that trigger the signedness error, causing the target system to crash or become unresponsive. The impact extends beyond simple service disruption as it can affect entire network authentication infrastructures, particularly in environments where Kerberos is the primary authentication mechanism for services like LDAP, HTTP, or other network protocols that depend on Kerberos for secure communication. This vulnerability directly maps to ATT&CK technique T1499.004, which describes network disruption through service availability attacks, and T1566.001, which involves phishing with malicious attachments or links that could be used to deliver the exploit.
The mitigation strategy for this vulnerability requires immediate patching of all affected MIT Kerberos V5 installations to versions 1.2.5 or later where the integer signedness error has been corrected. System administrators should also implement network monitoring to detect unusual ASN.1 packet patterns that might indicate exploitation attempts, while maintaining regular security updates for all authentication infrastructure components. Additional defensive measures include implementing proper input validation at network boundaries and configuring intrusion detection systems to monitor for malformed ASN.1 data structures that could indicate attempts to exploit this vulnerability. Organizations should also conduct thorough vulnerability assessments to identify all systems running affected versions of Kerberos and ensure proper patch management protocols are in place to prevent similar issues from occurring in the future.