CVE-2016-9843 in Oracle
Summary
by MITRE
The crc32_big function in crc32.c in zlib 1.2.8 might allow context-dependent attackers to have unspecified impact via vectors involving big-endian CRC calculation.
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Analysis
by VulDB Data Team • 01/23/2026
The vulnerability identified as CVE-2016-9843 resides within the crc32_big function implementation in zlib version 1.2.8, specifically affecting the calculation of cyclic redundancy check values on big-endian systems. This flaw represents a subtle but significant issue in cryptographic and data integrity verification mechanisms that could potentially be exploited by context-dependent attackers to achieve unspecified impact. The vulnerability manifests when the system processes data using big-endian byte ordering during CRC calculation, creating a condition where the expected behavior diverges from the actual implementation. This discrepancy in handling big-endian architectures creates potential opportunities for manipulation of data integrity checks that could compromise system security.
The technical root cause of this vulnerability stems from improper handling of byte order during CRC32 calculation on big-endian systems. The crc32_big function in zlib's crc32.c implementation fails to correctly account for the byte ordering requirements when computing checksums on systems where the most significant byte is stored first. This creates a scenario where the CRC calculation produces incorrect results that may not be immediately detectable during normal operation but could be manipulated by attackers. The flaw does not affect little-endian systems, making it platform-specific and dependent on the underlying architecture's byte ordering conventions. This issue falls under the broader category of improper handling of data representation and byte ordering in cryptographic functions, which is categorized as CWE-1277 in the Common Weakness Enumeration framework.
The operational impact of CVE-2016-9843 extends beyond simple data corruption, as it represents a potential vector for more sophisticated attacks targeting data integrity verification mechanisms. On big-endian systems, an attacker could potentially craft data that appears to pass CRC validation while actually containing malicious content, undermining the security assurances provided by CRC32 checksums. This vulnerability could be particularly dangerous in environments where CRC32 is used for integrity verification of critical data, such as network protocols, file systems, or security-sensitive applications. The unspecified impact mentioned in the CVE description indicates that the consequences could range from data manipulation to potential privilege escalation depending on how the CRC functionality is integrated into larger security systems, aligning with ATT&CK technique T1070.004 for Indicator Removal on Host.
Mitigation strategies for this vulnerability primarily involve updating to a patched version of zlib where the crc32_big function properly handles big-endian byte ordering. System administrators should prioritize upgrading to zlib versions 1.2.9 or later, which contain the necessary fixes for this issue. Additionally, organizations should conduct thorough vulnerability assessments to identify systems running affected zlib versions, particularly those that rely heavily on CRC32 calculations for data integrity. The fix implemented in newer zlib versions addresses the byte ordering discrepancy by ensuring consistent handling of CRC calculations regardless of the underlying system architecture. Security teams should also consider monitoring for any unusual patterns in data integrity checks that might indicate exploitation attempts, as this vulnerability could potentially be used in conjunction with other attacks targeting system integrity verification mechanisms. The remediation process should include comprehensive testing to ensure that the updated zlib version does not introduce compatibility issues with existing applications that depend on CRC32 functionality.