CVE-2014-3468 in Libtasn1
Summary
by MITRE
The asn1_get_bit_der function in GNU Libtasn1 before 3.6 does not properly report an error when a negative bit length is identified, which allows context-dependent attackers to cause out-of-bounds access via crafted ASN.1 data.
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Analysis
by VulDB Data Team • 06/20/2021
The vulnerability identified as CVE-2014-3468 resides within the GNU Libtasn1 library version 3.5 and earlier, representing a critical flaw in the ASN.1 (Abstract Syntax Notation One) parsing mechanism that governs the encoding and decoding of structured data. This library serves as a fundamental component in various cryptographic applications and security protocols that rely on ASN.1 for data representation, making the flaw particularly dangerous in environments where secure communication and data integrity are paramount. The vulnerability specifically manifests in the asn1_get_bit_der function which is responsible for extracting bit string data from DER (Distinguished Encoding Rules) encoded ASN.1 structures, a process that requires strict validation of data boundaries and length parameters.
The technical flaw stems from the improper error handling mechanism within the asn1_get_bit_der function where it fails to correctly identify and report errors when encountering negative bit lengths in ASN.1 data structures. This occurs because the function does not adequately validate the bit length parameter before proceeding with memory operations, allowing maliciously crafted ASN.1 data to contain negative values that would normally trigger an error condition. When the function processes such malformed data, it interprets the negative bit length as a valid parameter and proceeds to perform memory operations based on this invalid input, creating a scenario where memory access occurs beyond the intended boundaries. This type of vulnerability falls under CWE-129, specifically addressing improper validation of length parameters, and represents a classic example of an out-of-bounds read condition that can be exploited to access memory locations that should remain protected.
The operational impact of this vulnerability extends beyond simple memory corruption, as it enables context-dependent attackers to potentially execute arbitrary code or cause denial of service conditions within applications that utilize the vulnerable GNU Libtasn1 library. Attackers can craft specific ASN.1 data structures containing negative bit length values and feed them to applications that depend on Libtasn1 for parsing cryptographic data, such as SSL/TLS implementations, certificate processing systems, or any security infrastructure that handles ASN.1 encoded information. The attack vector is particularly concerning because it requires minimal privileges and can be executed through legitimate data processing pathways, making it difficult to detect and prevent through traditional network monitoring approaches. From an ATT&CK framework perspective, this vulnerability aligns with techniques involving execution through library loading and data manipulation, potentially enabling privilege escalation or information disclosure attacks depending on the target application's memory layout and access controls.
Mitigation strategies for CVE-2014-3468 focus primarily on upgrading to GNU Libtasn1 version 3.6 or later, where the error handling in the asn1_get_bit_der function has been corrected to properly detect and reject negative bit lengths. System administrators should prioritize patching all affected applications and services that rely on the vulnerable library, particularly those handling cryptographic certificates, secure communications, or any ASN.1 encoded data processing. Additionally, implementing runtime protections such as stack canaries, address space layout randomization, and memory protection mechanisms can help mitigate potential exploitation attempts, though these measures provide only partial defense since the vulnerability lies within the core library functionality. Organizations should also consider implementing input validation controls at application layers to detect and reject malformed ASN.1 data before it reaches the vulnerable library functions, providing an additional defense-in-depth measure that can help protect against exploitation attempts even if the underlying library is not immediately patched.