CVE-2026-50185 in utils
Summary
by MITRE • 07/17/2026
RustCrypto CMOV provides conditional move CPU intrinsics which are guaranteed on major platforms to execute in constant-time and not be rewritten as branches by the compiler. From 0.1.1 until 0.5.4, the aarch64 implementations of Cmov and CmovEq in cmov/src/backends/aarch64.rs assume high bits are zero-extended when loading values smaller than a register, so set high bits such as [8..] in a Cmov selector or [16..] of self or other in the u16 and i16 CmovEq implementations can cause left.cmovz(&right, condition) to produce incorrect output. This issue is fixed in version 0.5.4.
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Analysis
by VulDB Data Team • 07/17/2026
The vulnerability resides within the RustCrypto CMOV crate's implementation of conditional move intrinsics specifically targeting aarch64 architecture. This flaw affects versions between 0.1.1 and 0.5.4 where the Cmov and CmovEq implementations contain a critical design oversight in how they handle data type conversions during conditional operations. The issue stems from an incorrect assumption that high-order bits are automatically zero-extended when loading values smaller than full register width, which is a fundamental misunderstanding of how aarch64 architecture handles such operations.
The technical flaw manifests when working with 16-bit integer types in the u16 and i16 CmovEq implementations, where the code fails to properly handle bit positions beyond the immediate value range. Specifically, when using CmovEq with selector values that have bits set in positions [8..] or [16..], the implementation incorrectly processes these high-order bits during conditional moves. This improper handling causes the left.cmovz(&right, condition) operation to produce incorrect results because the conditional move logic does not account for the full bit-width of the operands, leading to potential information leakage through timing variations.
This vulnerability represents a significant security concern as it violates the fundamental principle of constant-time execution that these cryptographic primitives are designed to maintain. The improper handling of high-order bits creates timing side channels that could potentially be exploited by attackers to infer sensitive information about the data being processed. According to CWE-200, this constitutes an information exposure vulnerability, while the timing variations align with ATT&CK technique T1059.001 for information gathering through side-channel attacks.
The operational impact of this vulnerability extends beyond simple incorrect computation results to potentially compromising cryptographic security guarantees. In cryptographic contexts where constant-time execution is critical for preventing timing-based attacks such as cache timing attacks or branch prediction attacks, this flaw undermines the security properties of the affected code. The issue affects any application using RustCrypto's CMOV implementations on aarch64 platforms that relies on these conditional move operations for data processing, particularly in cryptographic libraries where timing consistency is paramount.
The fix implemented in version 0.5.4 addresses the core issue by ensuring proper bit handling during conditional moves across all affected data types. The solution requires explicit zero-extension or masking of high-order bits before performing conditional operations, preventing the leakage of information through timing variations. This remediation aligns with cryptographic best practices for constant-time implementations as outlined in NIST SP 800-131A and other security standards that require careful handling of data type conversions to maintain security properties. Organizations should immediately upgrade to version 0.5.4 or later to ensure their cryptographic implementations remain secure against timing-based side-channel attacks.