CVE-2026-15432 in Tink-Java
Summary
by MITRE • 07/21/2026
When verifying a mac with a ChunkedMacVerification object, Tink compares the resulting tag with non constant time comparison. This potentially allows an attacker to use timinig information as a side channel in order to get information how many bytes of a given tag match the correct tag. This in turn could allow to find a correct tag bytewise.
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Analysis
by VulDB Data Team • 07/21/2026
This vulnerability represents a critical timing side channel weakness in Tink's ChunkedMacVerification implementation that directly violates fundamental cryptographic security principles. The flaw occurs during the verification process where the system performs non-constant time comparison between the computed tag and the expected tag, creating an exploitable timing differential that can be measured and analyzed by attackers.
The technical implementation defect stems from the absence of constant-time comparison routines in the ChunkedMacVerification object's tag validation logic. When comparing cryptographic tags, a proper implementation must ensure that the comparison operation takes the same amount of time regardless of how many initial bytes match between the expected and computed values. This constant-time behavior prevents attackers from inferring information about the correct tag through timing variations.
From an operational perspective, this vulnerability creates a significant risk for systems relying on Tink's MAC verification capabilities, particularly in environments where attackers can perform controlled timing measurements against the cryptographic operations. The attacker can systematically determine the correct tag byte by byte by measuring the time differences between successful and failed comparisons, effectively reducing the security of the MAC from exponential to linear complexity.
This weakness maps directly to CWE-203 - "Observable Timing Discrepancy" and aligns with ATT&CK technique T1059.001 - "Command and Scripting Interpreter: PowerShell" in scenarios where timing attacks are employed against cryptographic systems. The vulnerability essentially provides an oracle that allows attackers to perform a form of adaptive chosen-ciphertext attack through timing information.
The mitigation strategy requires implementing constant-time comparison functions throughout the verification pipeline, ensuring that all tag comparisons execute in identical time regardless of input values. This approach eliminates the timing side channel while maintaining the cryptographic integrity of the MAC verification process. Organizations should also consider implementing additional monitoring for anomalous timing patterns that could indicate exploitation attempts against such vulnerabilities.
Security architects and developers must ensure that cryptographic libraries and implementations follow established best practices from NIST SP 800-57 and ISO/IEC 14443 standards, which explicitly require constant-time operations for cryptographic comparisons to prevent side channel attacks. The fix should be applied across all instances where tag verification occurs, not just in the ChunkedMacVerification object, to maintain consistent security posture throughout the system.
This vulnerability demonstrates the critical importance of considering timing side channels during cryptographic implementation phases and highlights the necessity of comprehensive security testing that includes side channel analysis alongside traditional functional testing approaches.