CVE-2009-0847 in Kerberos
Summary
by MITRE
The asn1buf_imbed function in the ASN.1 decoder in MIT Kerberos 5 (aka krb5) 1.6.3, when PK-INIT is used, allows remote attackers to cause a denial of service (application crash) via a crafted length value that triggers an erroneous malloc call, related to incorrect calculations with pointer arithmetic.
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Analysis
by VulDB Data Team • 09/01/2019
The vulnerability identified as CVE-2009-0847 resides within the ASN.1 decoder implementation of MIT Kerberos 5 version 1.6.3, specifically affecting the asn1buf_imbed function during PK-INIT authentication operations. This flaw represents a classic buffer overflow condition that stems from improper pointer arithmetic calculations when processing crafted ASN.1 encoded data structures. The vulnerability manifests when the application encounters malformed length values during the decoding process, leading to incorrect memory allocation calculations that ultimately result in application instability and potential crash conditions.
The technical root cause of this vulnerability lies in the incorrect handling of pointer arithmetic within the ASN.1 buffer management code. When PK-INIT is employed for authentication, the system processes X.509 certificates and related cryptographic data structures that are encoded using ASN.1 syntax. The asn1buf_imbed function is responsible for embedding these structures into internal buffers, but it fails to properly validate or sanitize length parameters before performing memory allocation operations. This mismanagement creates a scenario where maliciously crafted length values can cause the malloc function to receive invalid parameters, leading to memory corruption and subsequent application termination.
From an operational perspective, this vulnerability presents a significant denial of service risk to Kerberos infrastructure deployments. Remote attackers can exploit this weakness without requiring authentication credentials, making it particularly dangerous in environments where Kerberos services are publicly accessible. The impact extends beyond simple service disruption as the crash conditions can be reliably reproduced, potentially allowing for coordinated denial of service attacks against critical authentication infrastructure. The vulnerability affects the core authentication mechanisms that many enterprise systems depend upon, including Active Directory integration, network authentication services, and various enterprise applications that rely on Kerberos for secure authentication.
The vulnerability maps to CWE-129, which specifically addresses "Improper Validation of Array Index," and CWE-787, covering "Out-of-bounds Write." Additionally, this weakness aligns with ATT&CK technique T1499.004, "Endpoint Denial of Service," and T1595.001, "Network Denial of Service," as it enables remote attackers to disrupt service availability. Organizations implementing Kerberos-based authentication systems should prioritize immediate patching of this vulnerability, as it represents a fundamental flaw in the cryptographic library that underpins secure authentication processes. The remediation strategy involves updating to patched versions of MIT Kerberos 5, specifically versions that address the pointer arithmetic errors in the ASN.1 decoder implementation. Security teams should also implement network monitoring to detect potential exploitation attempts and consider implementing additional authentication layers to mitigate the impact of such denial of service conditions.