CVE-2019-10071 in Tapestry
Summary
by MITRE
The code which checks HMAC in form submissions used String.equals() for comparisons, which results in a timing side channel for the comparison of the HMAC signatures. This could lead to remote code execution if an attacker is able to determine the correct signature for their payload. The comparison should be done with a constant time algorithm instead.
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Analysis
by VulDB Data Team • 08/11/2020
The vulnerability identified as CVE-2019-10071 represents a critical timing side channel weakness in HMAC signature validation mechanisms within form submission processing. This flaw stems from the implementation of string comparison operations that utilize Java's standard String.equals() method, which exhibits variable execution time based on the position of the first mismatched character. The timing variation creates a measurable difference in response times that can be exploited by attackers to perform statistical analysis and gradually determine the correct HMAC signature through repeated submissions. The vulnerability falls under CWE-203, which specifically addresses the exposure of sensitive information through timing side channels, and aligns with ATT&CK technique T1211 where adversaries leverage timing discrepancies to infer system behavior and potentially bypass security controls.
The technical implementation flaw manifests when the system processes form submissions containing HMAC signatures for validation purposes. During the comparison phase, the String.equals() method performs character-by-character evaluation from left to right, meaning that if the first few characters match, the comparison continues for potentially many more iterations before a mismatch is detected. This creates a measurable timing differential that an attacker can exploit through repeated requests, where each failed comparison provides information about the correct signature. The vulnerability is particularly dangerous because it allows attackers to perform a brute force attack on the HMAC signature without triggering obvious security mechanisms, as the timing variations are subtle and can be masked within normal network latency fluctuations.
The operational impact of this vulnerability extends beyond simple authentication bypass to potentially enable full remote code execution when combined with other attack vectors or when the system's HMAC signatures control access to privileged operations. An attacker who successfully determines the correct HMAC signature can manipulate form submissions to execute arbitrary code or gain unauthorized access to system resources. The timing side channel makes this attack more efficient than traditional brute force approaches, as the attacker can reduce the search space through statistical analysis rather than random guessing. This vulnerability particularly affects web applications that rely on HMAC signatures for form integrity validation, including those implementing CSRF protection mechanisms or API authentication systems that depend on signature verification.
Mitigation strategies for CVE-2019-10071 require immediate implementation of constant-time comparison algorithms that ensure equal execution time regardless of input differences. The recommended solution involves replacing String.equals() with cryptographic libraries that provide constant-time comparison functions such as those found in the Apache Commons Codec library or similar security-focused implementations. Security practitioners should also consider implementing additional protections including rate limiting, request throttling, and monitoring for unusual timing patterns in system responses. The fix must be applied across all form submission validation points where HMAC signatures are verified, ensuring that no other parts of the application codebase contain similar timing side channel vulnerabilities. Organizations should conduct comprehensive code reviews to identify other instances of variable-time string comparisons and implement automated testing to detect such patterns in future development cycles, aligning with security standards that emphasize the importance of constant-time operations in cryptographic implementations.