CVE-2006-0645 in libtasn1
Summary
by MITRE
Tiny ASN.1 Library (libtasn1) before 0.2.18, as used by (1) GnuTLS 1.2.x before 1.2.10 and 1.3.x before 1.3.4, and (2) GNU Shishi, allows attackers to crash the DER decoder and possibly execute arbitrary code via "out-of-bounds access" caused by invalid input, as demonstrated by the ProtoVer SSL test suite.
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Analysis
by VulDB Data Team • 06/22/2025
The vulnerability identified as CVE-2006-0645 represents a critical security flaw in the Tiny ASN.1 Library (libtasn1) version 0.2.17 and earlier, which affected multiple prominent security implementations including GnuTLS and GNU Shishi. This vulnerability stems from improper handling of malformed ASN.1 encoded data during the DER (Distinguished Encoding Rules) decoding process, creating a path for remote attackers to potentially cause system crashes or execute arbitrary code through carefully crafted malicious input. The flaw specifically manifests as an out-of-bounds memory access condition that occurs when the library processes invalid ASN.1 structures, particularly those that do not conform to expected encoding standards.
The technical nature of this vulnerability aligns with CWE-125, which describes out-of-bounds read conditions, and CWE-787, which covers out-of-bounds writes in buffer operations. The flaw occurs within the ASN.1 decoder implementation where insufficient input validation allows attackers to manipulate the parsing logic through malformed data structures. When the library encounters invalid ASN.1 input during DER decoding, it fails to properly bounds-check array accesses or validate structure lengths, leading to memory corruption that can result in program termination or arbitrary code execution. The vulnerability is particularly concerning because it affects widely deployed security libraries, with GnuTLS 1.2.x versions before 1.2.10 and 1.3.x versions before 1.3.4 being specifically impacted, along with GNU Shishi implementations.
From an operational perspective, this vulnerability creates significant risk for systems relying on these security libraries for SSL/TLS operations and authentication protocols. The ProtoVer SSL test suite demonstration shows that attackers can trigger the vulnerability through standard SSL/TLS handshake sequences, potentially allowing for denial-of-service attacks or remote code execution in vulnerable systems. The impact extends beyond simple crashes since the out-of-bounds access could enable attackers to manipulate memory layout and potentially execute malicious code with the privileges of the affected process. This vulnerability represents a classic example of how flaws in cryptographic libraries can have cascading effects across entire security infrastructures, as both GnuTLS and GNU Shishi are widely used components in various operating systems and network security applications.
The remediation strategy involves upgrading to libtasn1 version 0.2.18 or later, which includes proper bounds checking and input validation mechanisms to prevent the out-of-bounds memory access conditions. System administrators should prioritize patching affected GnuTLS installations, particularly versions 1.2.x before 1.2.10 and 1.3.x before 1.3.4, along with GNU Shishi implementations. Additionally, implementing network segmentation and monitoring for suspicious ASN.1 encoded traffic can help detect exploitation attempts. From an ATT&CK framework perspective, this vulnerability maps to techniques involving privilege escalation and execution through malformed input, with the initial access potentially occurring through network-based attacks targeting SSL/TLS services. Organizations should also consider implementing application-level firewalls and input sanitization measures to reduce the attack surface, as the vulnerability demonstrates how cryptographic libraries can become entry points for sophisticated attacks.