CVE-2016-9939 in Crypto++
Summary
by MITRE
Crypto++ (aka cryptopp and libcrypto++) 5.6.4 contained a bug in its ASN.1 BER decoding routine. The library will allocate a memory block based on the length field of the ASN.1 object. If there is not enough content octets in the ASN.1 object, then the function will fail and the memory block will be zeroized even if its unused. There is a noticeable delay during the wipe for a large allocation.
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Analysis
by VulDB Data Team • 09/15/2024
The vulnerability identified as CVE-2016-9939 affects Crypto++ version 5.6.4, a widely-used C++ cryptographic library that implements various encryption algorithms and protocols. This flaw resides within the ASN.1 Basic Encoding Rules (BER) decoding functionality, which is fundamental to parsing cryptographic objects such as certificates, keys, and signatures. The issue manifests when the library processes malformed ASN.1 structures where the length field indicates a larger memory allocation than the actual available content octets. This discrepancy creates a specific scenario where the library allocates memory based on the deceptive length field before discovering the insufficient data, resulting in a delayed memory wipe operation.
The technical implementation of this vulnerability stems from how Crypto++ handles memory allocation during ASN.1 parsing operations. When the library encounters an ASN.1 object with a length field that exceeds the actual available data, it proceeds with the allocation based on the specified length before validating the content. This design flaw causes the system to allocate memory blocks that may be significantly larger than necessary, and when the validation fails, the library executes a zeroization routine on these allocations. The zeroization process introduces a measurable delay, particularly when dealing with large memory blocks, creating a potential timing-based side channel attack vector.
From an operational perspective, this vulnerability presents a significant risk in environments where Crypto++ is used for processing untrusted input data such as X.509 certificates, PKCS#7 signatures, or other ASN.1-encoded cryptographic objects. The timing characteristics introduced by the delayed memory wiping can be exploited by attackers to perform timing attacks that infer information about the system's internal state or the nature of the processed data. This weakness aligns with CWE-122, which describes buffer overflow vulnerabilities in heap-based data structures, and represents a specific implementation issue where memory management practices create predictable timing behavior. The vulnerability is particularly concerning in applications that process large volumes of cryptographic objects, as the delay accumulates and becomes more pronounced with larger allocations.
The impact of CVE-2016-9939 extends beyond simple performance degradation to potential information disclosure through timing side channels. Attackers can leverage the predictable delay patterns to distinguish between different types of malformed input or to infer properties about the cryptographic processing pipeline. This vulnerability is categorized under the ATT&CK framework as a timing attack technique, specifically targeting the memory management and processing behavior of cryptographic libraries. Organizations using Crypto++ in security-critical applications should prioritize immediate mitigation through library updates, as the vulnerability represents a fundamental flaw in the memory allocation and validation sequence that could be exploited in various attack scenarios. The fix typically involves implementing proper bounds checking before memory allocation and avoiding unnecessary zeroization of unused memory blocks, thereby eliminating the timing artifacts that make this vulnerability exploitable.