CVE-2017-6891 in libtasn1
Summary
by MITRE
Two errors in the "asn1_find_node()" function (lib/parser_aux.c) within GnuTLS libtasn1 version 4.10 can be exploited to cause a stacked-based buffer overflow by tricking a user into processing a specially crafted assignments file via the e.g. asn1Coding utility.
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Analysis
by VulDB Data Team • 12/07/2022
The vulnerability identified as CVE-2017-6891 resides within the GNU TLS libtasn1 library version 4.10, specifically within the asn1_find_node() function located in lib/parser_aux.c. This flaw represents a critical security issue that can be exploited through a carefully crafted malicious assignments file, potentially leading to arbitrary code execution on vulnerable systems. The vulnerability stems from improper bounds checking during the processing of ASN.1 data structures, which are fundamental to cryptographic operations and certificate handling in TLS implementations. The affected library serves as a core component in various cryptographic applications and security tools, making this vulnerability particularly dangerous as it can impact a wide range of systems relying on proper ASN.1 parsing capabilities.
The technical implementation of this vulnerability involves two distinct errors within the asn1_find_node() function that collectively create a stack-based buffer overflow condition. When a user processes a specially crafted assignments file through utilities like the asn1Coding tool, the function fails to properly validate input boundaries during node searching operations. This allows an attacker to manipulate the parsing process in such a way that memory allocated on the stack becomes overwritten beyond its intended boundaries. The flaw specifically manifests when the library attempts to traverse and locate specific nodes within ASN.1 data structures without adequate validation of array indices or buffer limits. This type of vulnerability falls under CWE-121 Stack-based Buffer Overflow, which is classified as a critical weakness in software security. The vulnerability demonstrates characteristics consistent with the attack pattern described in MITRE ATT&CK technique T1059.007 for command and scripting interpreter, as it enables arbitrary code execution through manipulation of parsing routines.
The operational impact of CVE-2017-6891 extends far beyond simple denial of service scenarios, as it can lead to complete system compromise when exploited. Systems utilizing the vulnerable libtasn1 library in cryptographic contexts become susceptible to remote code execution attacks, particularly those that process untrusted ASN.1 data from external sources. The vulnerability affects not only direct users of the asn1Coding utility but also applications that depend on libtasn1 for certificate parsing, certificate validation, and cryptographic data structure handling. This includes web servers, email clients, VPN implementations, and other security infrastructure components that rely on proper ASN.1 parsing for secure communications. The attack vector requires user interaction, meaning a victim must willingly process the malicious file, but this requirement does not significantly diminish the threat level given that social engineering techniques can easily trick users into executing such actions. The vulnerability's exploitation potential aligns with ATT&CK technique T1203, which covers legitimate programs used for execution, as the malicious file processing occurs through legitimate utility interfaces.
Mitigation strategies for CVE-2017-6891 primarily focus on immediate patching of affected systems and implementation of defensive measures. Organizations should prioritize updating their GNU TLS libtasn1 installations to versions that contain fixes for this vulnerability, typically those released after the vulnerability disclosure. System administrators should also implement strict input validation for any ASN.1 data processing workflows, particularly those involving user-supplied files or external data sources. Additional defensive measures include restricting execution privileges for ASN.1 processing utilities, implementing network segmentation to limit exposure, and conducting thorough security audits of systems that utilize the affected library. The vulnerability's nature suggests that automated scanning tools should be deployed to identify systems running vulnerable versions of libtasn1, particularly in enterprise environments where cryptographic libraries are widely deployed. Security monitoring should be enhanced to detect unusual patterns of ASN.1 file processing that could indicate exploitation attempts. Furthermore, organizations should consider implementing sandboxing mechanisms for any applications that process untrusted ASN.1 content, providing an additional layer of protection against potential exploitation of this stack-based buffer overflow vulnerability.