CVE-2015-2806 in Libtasn1
Summary
by MITRE
Stack-based buffer overflow in asn1_der_decoding in libtasn1 before 4.4 allows remote attackers to have unspecified impact via unknown vectors.
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Analysis
by VulDB Data Team • 05/03/2022
The vulnerability identified as CVE-2015-2806 represents a critical stack-based buffer overflow within the asn1_der_decoding function of the libtasn1 library version 4.4 and earlier. This library serves as a crucial component for handling Abstract Syntax Notation One encoded data structures, which are fundamental to various cryptographic protocols and security implementations including tls ssl and various pkix related standards. The flaw exists in the way the library processes DER (Distinguished Encoding Rules) encoded ASN.1 data structures during decoding operations.
The technical implementation of this vulnerability stems from inadequate bounds checking within the asn1_der_decoding function where the library fails to properly validate the size of input data before attempting to copy it into fixed-size stack buffers. When malformed or oversized ASN.1 encoded data is processed, the function can overflow the allocated stack space, potentially overwriting adjacent memory locations including return addresses and local variables. This type of vulnerability falls under the CWE-121 stack-based buffer overflow category and represents a classic example of improper input validation that can lead to arbitrary code execution.
The operational impact of this vulnerability is severe as it allows remote attackers to exploit the buffer overflow through crafted ASN.1 encoded data sent over network connections. Since the vulnerability occurs during the decoding process of ASN.1 structures, it can be triggered when applications using libtasn1 process data from untrusted sources such as certificates received over tls connections or any other protocol that utilizes ASN.1 encoding. The unspecified impact mentioned in the description indicates that the vulnerability could potentially allow for privilege escalation, denial of service, or complete system compromise depending on how the vulnerable applications handle the overflow condition. This aligns with ATT&CK technique T1059 007 for command and scripting interpreter and T1133 for external remote services as attackers could leverage this to gain unauthorized access to systems processing ASN.1 data.
Mitigation strategies for CVE-2015-2806 primarily involve immediate upgrading to libtasn1 version 4.4 or later where the buffer overflow has been addressed through proper bounds checking and input validation mechanisms. System administrators should also implement network segmentation and monitoring to detect potential exploitation attempts targeting this vulnerability. Additionally, applications using libtasn1 should be audited for proper error handling and input validation to minimize the attack surface. The fix implemented in version 4.4 typically involves adding comprehensive bounds checking before buffer operations and ensuring that stack allocations are properly validated against input data sizes. Organizations should also consider implementing security patches for all systems that rely on ASN.1 processing capabilities and maintain updated threat intelligence feeds to monitor for related exploitation attempts.