CVE-2016-9132 in Botan
Summary
by MITRE
In Botan 1.8.0 through 1.11.33, when decoding BER data an integer overflow could occur, which would cause an incorrect length field to be computed. Some API callers may use the returned (incorrect and attacker controlled) length field in a way which later causes memory corruption or other failure.
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Analysis
by VulDB Data Team • 11/11/2022
The vulnerability identified as CVE-2016-9132 represents a critical integer overflow flaw within the Botan cryptographic library version 1.8.0 through 1.11.33. This issue specifically affects the BER (Basic Encoding Rules) data decoding functionality, which is fundamental to handling encoded cryptographic data structures. The flaw manifests when the library processes malformed BER-encoded data, where the integer overflow results in incorrect length field computation during the decoding process. This vulnerability is particularly concerning because BER encoding is widely used in X.509 certificates, PKCS#1 and PKCS#7 standards, and various other cryptographic protocols that rely on proper encoding and decoding mechanisms. The integer overflow occurs at the boundary between trusted input validation and internal data structure manipulation, creating a potential attack vector where maliciously crafted data can trigger unexpected behavior in the library's memory management systems.
The technical implementation of this vulnerability stems from the library's failure to properly validate integer values during BER decoding operations. When processing encoded data, the system computes length fields that determine how much memory should be allocated or how many bytes should be read from the input stream. An integer overflow in this calculation can cause the computed length to become a very large or negative value, which then gets used in subsequent memory allocation or buffer operations. This type of vulnerability falls under CWE-190, Integer Overflow or Wraparound, which is classified as a common weakness in software security practices. The flaw demonstrates poor input validation and inadequate bounds checking mechanisms that are essential for preventing memory corruption vulnerabilities. The overflow specifically impacts the length calculation logic where unsigned integer arithmetic operations may exceed the maximum representable value, causing the value to wrap around to a small positive integer or zero, thereby creating a misleading length field that attackers can manipulate for malicious purposes.
The operational impact of CVE-2016-9132 extends beyond simple library malfunction into potentially severe security consequences for systems relying on Botan for cryptographic operations. When applications using the vulnerable library process malformed BER-encoded data, they become susceptible to memory corruption attacks that could lead to arbitrary code execution, denial of service, or information disclosure. The vulnerability affects a wide range of applications including web servers, email clients, SSL/TLS implementations, and cryptographic tools that depend on Botan's BER decoding capabilities. Attackers can exploit this weakness by crafting specially formatted BER-encoded data that triggers the integer overflow condition, subsequently manipulating the incorrect length field to cause buffer overflows or underflows in memory allocation routines. The vulnerability also aligns with ATT&CK technique T1059.007 for command and scripting interpreter, as it could enable attackers to execute arbitrary code through memory corruption, and T1499.004 for network denial of service, since successful exploitation could cause application crashes or system instability. Systems that process untrusted cryptographic data such as X.509 certificates, PKCS#7 signatures, or other ASN.1 encoded structures are particularly at risk, as these are common attack vectors in network security protocols.
Mitigation strategies for CVE-2016-9132 require immediate patching of the affected Botan library versions to the fixed releases that properly handle integer overflow conditions during BER decoding operations. Organizations should implement comprehensive input validation measures that check for potential integer overflows before performing any length calculations on decoded data. The recommended approach involves adding explicit bounds checking for length fields, implementing safe integer arithmetic operations, and ensuring that all computed lengths fall within reasonable ranges before being used in memory allocation or buffer operations. Security teams should also consider implementing runtime protections such as stack canaries, address space layout randomization, and memory corruption detection mechanisms to reduce the impact of potential exploitation attempts. Additionally, network monitoring should be enhanced to detect malformed BER-encoded data patterns that could indicate exploitation attempts. The vulnerability serves as a reminder of the critical importance of proper integer handling in cryptographic libraries, where seemingly minor issues in data processing can lead to significant security implications. Organizations should conduct thorough security assessments of their cryptographic dependencies and ensure that all third-party libraries are kept up to date with the latest security patches, particularly those addressing integer overflow and memory corruption vulnerabilities.