CVE-2016-4008 in Libtasn1
Summary
by MITRE
The _asn1_extract_der_octet function in lib/decoding.c in GNU Libtasn1 before 4.8, when used without the ASN1_DECODE_FLAG_STRICT_DER flag, allows remote attackers to cause a denial of service (infinite recursion) via a crafted certificate.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 07/29/2022
The vulnerability identified as CVE-2016-4008 represents a critical denial of service flaw within the GNU Libtasn1 library version 4.7 and earlier. This library serves as a crucial component for handling asn1 encoding and decoding operations in various security applications including gnutls and other cryptographic tools. The vulnerability specifically resides in the _asn1_extract_der_octet function located in the lib/decoding.c file, which processes data according to the Abstract Syntax Notation One standard used extensively in PKI infrastructure and cryptographic protocols. When the ASN1_DECODE_FLAG_STRICT_DER flag is not properly set during certificate processing, the function becomes susceptible to malformed input that triggers recursive processing patterns.
The technical flaw manifests as a lack of proper input validation and recursion depth checking within the ASN1 decoding process. Attackers can craft specially formatted certificates that contain malformed octet strings or nested structures that cause the _asn1_extract_der_octet function to repeatedly call itself without proper termination conditions. This infinite recursion eventually exhausts system resources including stack space and processing power, leading to complete service unavailability. The vulnerability operates at the protocol level rather than exploiting memory corruption or injection flaws, making it particularly insidious as it can be triggered through legitimate certificate parsing operations without requiring special privileges or complex attack vectors.
The operational impact of this vulnerability extends beyond simple service disruption to encompass broader security implications for systems relying on GNU Libtasn1 for certificate validation and processing. Any application that uses this library for handling X.509 certificates or other ASN1-encoded data becomes vulnerable to this attack, including web servers, certificate authorities, and cryptographic tools. The attack can be executed remotely through any mechanism that processes certificates through the affected library, potentially affecting TLS/SSL connections, certificate validation services, and PKI infrastructure components. This makes the vulnerability particularly dangerous in environments where certificate processing is frequent or automated, as the denial of service can be sustained and difficult to detect.
Mitigation strategies for CVE-2016-4008 primarily involve upgrading to GNU Libtasn1 version 4.8 or later where the vulnerability has been addressed through proper recursion depth checking and input validation. System administrators should also implement strict certificate validation policies that enforce the ASN1_DECODE_FLAG_STRICT_DER flag during certificate processing operations. Additionally, monitoring for unusual resource consumption patterns and implementing rate limiting on certificate processing requests can help detect and prevent exploitation attempts. From a security framework perspective, this vulnerability aligns with CWE-674, which addresses Uncontrolled Recursion, and relates to ATT&CK technique T1499.004 for Network Denial of Service. Organizations should also consider implementing network segmentation and certificate validation firewalls to limit the impact of potential exploitation attempts while maintaining operational continuity.