CVE-2019-10013 in axTLS
Summary
by MITRE
The asn1_signature function in asn1.c in Cameron Hamilton-Rich axTLS through 2.1.5 has a Buffer Overflow that allows remote attackers to cause a denial of service (memory and CPU consumption) via a crafted certificate in the TLS certificate handshake message, because the result of get_asn1_length() is not checked for a minimum or maximum size.
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Analysis
by VulDB Data Team • 03/05/2024
The vulnerability identified as CVE-2019-10013 affects the axTLS library version 2.1.5 and earlier, specifically within the asn1_signature function located in the asn1.c file. This represents a critical buffer overflow flaw that stems from inadequate validation of ASN.1 length parameters during TLS certificate processing. The issue manifests when a remote attacker crafts a malicious certificate that contains malformed ASN.1 length values in the certificate handshake message, creating a condition where the get_asn1_length() function fails to validate whether the returned length falls within acceptable minimum and maximum boundaries.
The technical exploitation of this vulnerability occurs during the TLS certificate handshake process when the axTLS library attempts to parse certificate signatures. The asn1_signature function directly uses the output of get_asn1_length() without performing proper bounds checking against predefined size constraints. This oversight creates a scenario where an attacker can supply a certificate with an oversized or malformed ASN.1 length field, causing the library to allocate insufficient memory for processing the certificate data. The resulting buffer overflow leads to memory corruption that can trigger application crashes, memory exhaustion, or excessive cpu consumption during certificate validation.
From an operational perspective, this vulnerability presents a significant denial of service threat to systems utilizing the affected axTLS library. The impact extends beyond simple service disruption as the memory and cpu consumption patterns suggest that attackers could potentially leverage this flaw to consume system resources at an accelerated rate, leading to system instability or complete service unavailability. The remote nature of the attack means that any system accepting TLS connections and processing client certificates could be vulnerable, making this particularly concerning for network services, web servers, and any application that relies on axTLS for secure communications. The vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and represents a classic example of improper input validation in cryptographic libraries. The attack vector is consistent with ATT&CK technique T1071.001, which covers application layer protocol usage, specifically targeting TLS protocol implementations through malformed certificate handling.
The mitigation strategy for CVE-2019-10013 requires immediate upgrading to axTLS version 2.1.6 or later, which contains the necessary patches to validate ASN.1 length parameters before processing. Organizations should also implement certificate validation policies that include monitoring for unusual certificate patterns and consider deploying intrusion detection systems to identify potential exploitation attempts. Additionally, network segmentation and access controls should be implemented to limit exposure of systems that may be vulnerable to this specific attack vector, particularly those that process untrusted certificates from external sources. The fix addresses the root cause by introducing proper bounds checking that ensures the length values returned by get_asn1_length() are validated against predetermined minimum and maximum thresholds, preventing the allocation of memory that could lead to buffer overflow conditions.