Cmov/CmovEq on aarch64 can produce wrong results if high-bits of registers are set

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

5.5 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P · score source

EPSS

• CVE-2026-50185: 0.16% estimated exploitation activity in the next 30 days; percentile 4.88 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary The aarch64 implementations of Cmov and CmovEq seem to assume that the high bits when loading a value of size smaller than a register into a register are zero-extended. However, this is not the case and these bits are unspecified. This can result in a left.cmovz(&right, condition) not moving right into left, even if condition == 0. Details The Rust reference for inline assembly states that: If a value is of a smaller size than the register it is allocated in then the upper bits of that register will have an undefined value for inputs [..]. Reference If the high bits [8..] of the selector loaded into a register in the Cmov implementation or the high bits [16..] of self or other for CmovEq (specifically the implementation for u16 and i16) are set, the inline asm compares will produce a different result than the Rust code expects based on the narrow types. In other words, the following assert fails, even though condition as u8 is zero: Because the ninth bit is set in the…

Published by the source

2 Jul 2026, 17:18 UTC

Last modified by the source

2 Jul 2026, 17:18 UTC

Source last checked

26 Oct 2026, 15:42 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-3rjw-m598-pq24

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# Patch Next advisory brief: CVE-2026-50185

Advisory: Cmov/CmovEq on aarch64 can produce wrong results if high-bits of registers are set
IDs: CVE-2026-50185, GHSA-3rjw-m598-pq24
Record: https://patchnext.com/advisories/cve-2026-50185 (revision 1, source checked 26 Oct 2026, 15:42 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: cmov 0.5.4. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io cmov: affected >= 0.1.1, < 0.5.4; fixed in 0.5.4

## Suggested inspection (read-only)
- crates.io cmov: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on cmov.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-3rjw-m598-pq24 (GitHub-reviewed advisory GHSA-3rjw-m598-pq24 lists affected ranges: crates.io cmov >=0.1.1 <0.5.4)

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