{
  "affected": [
    {
      "affectedData": [
        {
          "product": "utils",
          "vendor": "RustCrypto",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 0.1.1, \u003c 0.5.4"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "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(\u0026right, condition) to produce incorrect output. This issue is fixed in version 0.5.4."
    }
  ],
  "id": "CVE-2026-50185",
  "lastModified": "2026-07-17T19:17:16.370",
  "metrics": {
    "cvssMetricV40": [
      {
        "cvssData": {
          "Automatable": "NOT_DEFINED",
          "Recovery": "NOT_DEFINED",
          "Safety": "NOT_DEFINED",
          "attackComplexity": "LOW",
          "attackRequirements": "PRESENT",
          "attackVector": "LOCAL",
          "availabilityRequirement": "NOT_DEFINED",
          "baseScore": 2.0,
          "baseSeverity": "LOW",
          "confidentialityRequirement": "NOT_DEFINED",
          "exploitMaturity": "NOT_DEFINED",
          "integrityRequirement": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
          "modifiedAttackRequirements": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedSubIntegrityImpact": "NOT_DEFINED",
          "modifiedUserInteraction": "NOT_DEFINED",
          "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
          "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
          "modifiedVulnIntegrityImpact": "NOT_DEFINED",
          "privilegesRequired": "LOW",
          "providerUrgency": "NOT_DEFINED",
          "subAvailabilityImpact": "NONE",
          "subConfidentialityImpact": "NONE",
          "subIntegrityImpact": "NONE",
          "userInteraction": "NONE",
          "valueDensity": "NOT_DEFINED",
          "vectorString": "CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
          "version": "4.0",
          "vulnAvailabilityImpact": "NONE",
          "vulnConfidentialityImpact": "NONE",
          "vulnIntegrityImpact": "LOW",
          "vulnerabilityResponseEffort": "NOT_DEFINED"
        },
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-07-17T19:17:16.370",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/RustCrypto/utils/commit/dba6c355c9f241e3726d5ec2a68f9f3b519f6063"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/RustCrypto/utils/releases/tag/cmov-v0.5.4"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/RustCrypto/utils/security/advisories/GHSA-3rjw-m598-pq24"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Received",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-758"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Primary"
    }
  ]
}

{
  "affected": [
    {
      "package": {
        "ecosystem": "crates.io",
        "name": "cmov"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.1.1"
            },
            {
              "fixed": "0.5.4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-50185"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-758"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-02T17:18:11Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Summary\n\nThe 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(\u0026right, condition)` not moving `right` into `left`, even if `condition == 0`. \n\n### Details\n\nThe Rust reference for inline assembly states that:\n\u003e 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](https://doc.rust-lang.org/reference/inline-assembly.html#r-asm.register-operands.smaller-value)\n\nIf 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.\n\nIn other words, the following assert fails, even though `condition as u8` is zero:\n```rust\nlet condition: u32 = black_box(1 \u003c\u003c 8);\nlet mut left = 1;\nlet right = 2;\nleft.cmovz(\u0026right, condition as u8);\nassert_eq!(left, right);\n```\nBecause the ninth bit is set in the original variable, this bit is also set when the truncated condition is loaded into the input register for the `cmp`, causing the `csel` to select the wrong value.\n\nThe problematic code is located in `cmov/src/backends/aarch64.rs` [here for Cmov](https://github.com/RustCrypto/utils/blob/dad5e3b9e66d929e86144fe7c8f25371892e35f3/cmov/src/backends/aarch64.rs#L4-L19) and [here for CmovEq](https://github.com/RustCrypto/utils/blob/dad5e3b9e66d929e86144fe7c8f25371892e35f3/cmov/src/backends/aarch64.rs#L60-L72).\n\nThe following function:\n```rust\n#[unsafe(no_mangle)]\npub fn cmovz_wrong_output(left: \u0026mut i32, right: i32, condition: u32) {\n    left.cmovz(\u0026right, condition as u8);\n}\n```\nproduces the assembly:\n```asm\ncmovz_wrong_output:\n\t.cfi_startproc\n\tldr w8, [x0]\n\t//APP\n\tcmp w2, #0\n\tcsel w8, w1, w8, eq\n\t//NO_APP\n\tstr w8, [x0]\n\tret\n```\n\nwhich compares the 32-bits of the condition value against 0, instead of the intended 8.\n\nSimilarly, the following function using `cmoveq`\n```rust\n#[unsafe(no_mangle)]\npub fn cmoveq_wrong_output(left: u32, right: u32, input: u8, output: \u0026mut u8) {\n    (left as u16).cmoveq(\u0026(right as u16), input, output);\n}\n```\ncompiles to:\n```asm\ncmoveq_wrong_output:\n\t.cfi_startproc\n\tldrb w8, [x3]\n\tand w9, w2, #0xff\n\t//APP\n\teor w10, w0, w1\n\tcmp w10, #0\n\tcsel w8, w9, w8, eq\n\t//NO_APP\n\tstrb w8, [x3]\n\tret\n```\nwhere 32 bits of left and right are compared instead of 16. The same happens for `i16`.\n\nFor CmovEq, it seems the `u8/i8` impls are not affected, as they are calling `u16::from` in [the implementation](https://github.com/RustCrypto/utils/blob/dad5e3b9e66d929e86144fe7c8f25371892e35f3/cmov/src/lib.rs#L119) which causes the upper bits to be masked out.\n\n### PoC\n\nThe following two test cases fail on `aarch64-unknown-linux-gnu` when compiled with `--release` (the cmovz one even in debug) emulated with qemu.\n\n```\n\u003e rustc --version\nrustc 1.94.0 (4a4ef493e 2026-03-02)\n```\n\n```rust\n#[cfg(test)]\nmod tests {\n    use core::hint::black_box;\n\n    use cmov::{Cmov, CmovEq};\n\n    #[test]\n    fn cmovz_wrong_output() {\n        // The black box is necessary here, as otherwise the compiler will \n        // provide a constant 0 to the csel\n        let condition: u32 = black_box(1 \u003c\u003c 8);\n        let mut left = 1;\n        let right = 2;\n        // I added this debug_assert as a sanity check, but funnily it causes\n        // the wrong cmov behavior in debug as well (as opposed to only in release mode without the debug_assert)\n        debug_assert_eq!(0, condition as u8);\n        left.cmovz(\u0026right, condition as u8);\n        assert_eq!(left, right);\n    }\n\n    #[test]\n    fn cmoveq_wrong_output() {\n        let input = 1;\n        let mut output = 0;\n        let left: u32 = black_box(1 \u003c\u003c 16);\n        let right: u32 = black_box(1 \u003c\u003c 17);\n        // asserting in release mode here would hide the bug, the debug_assert_eq is\n        // a sanity check that these values SHOULD be equal\n        debug_assert_eq!(left as u16, right as u16);\n        (left as u16).cmoveq(\u0026(right as u16), input, \u0026mut output);\n        assert_eq!(input, output);\n    }\n}\n```\n\n### Impact\n\nUnder specific circumstances, this issue can cause `Cmov/CmovEq` to produce incorrect output on `aarch64`. However, whether this bug can actually manifest depends on the surrounding code that calls the relevant impls. In the PoC, a narrowing cast is required, which masks out the set bits from Rust\u0027s point of view, but which are then used in the inline assembly. \n\n### Additional Finding\n\nPR [#1299](https://github.com/RustCrypto/utils/pull/1299) fixed a different bug in the aarch64 backend but introduced a small error. The `csel!` macro expect a `cmp` expression as its first argument which is never used. The compare is always `\"cmp {0:w}, 0\",` even for `csel64!`, which intends to use `cmp {0:x}, 0`. Given the bug described above, this oversight actually reduces its impact slightly, as only the bits in position`[8..32]` can cause issues,  even for those impls that use `csel64!`.",
  "id": "GHSA-3rjw-m598-pq24",
  "modified": "2026-07-02T17:18:11Z",
  "published": "2026-07-02T17:18:11Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/RustCrypto/utils/security/advisories/GHSA-3rjw-m598-pq24"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/RustCrypto/utils"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Cmov/CmovEq on aarch64 can produce wrong results if high-bits of registers are set "
}