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CmovApplication · Rustcrypto

CVE-2026-23519

CRITICAL · 9.8 CVSS v3.1 Published 2026-01-15
Fix available
A fix is available. Upgrade to 0.4.4 or later.
See remediation →
100/100
Remediation priority · Urgent
Public exploit Remotely reachable No privileges Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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. Prior to 0.4.4, the thumbv6m-none-eabi (Cortex M0, M0+ and M1) compiler emits non-constant time assembly when using cmovnz (portable version). This vulnerability is fixed in 0.4.4.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

The RustCrypto CMOV library provides constant-time conditional move intrinsics for cryptographic operations. Prior to version 0.4.4, when compiling for thumbv6m-none-eabi (ARM Cortex M0, M0+, M1) targets, the cmovnz portable implementation emits non-constant-time assembly that uses branches instead of true conditional moves. This breaks the constant-time guarantee and exposes cryptographic operations running on these microcontrollers to timing side-channel attacks.

MitigationUpgrade the rust-crypto-cmov dependency to version 0.4.4 or later. Reassess any cryptographic code deployed to ARM Cortex-M0/M0+/M1 devices that previously used this library to confirm the constant-time property is restored.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
CmovApplication
Affected:< 0.4.4

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Locate the rust-crypto-cmov dependency in your project
    Search your Cargo.lock file or Cargo.toml for 'cmov', 'rust-crypto-cmov', or similar CMOV crate references and note the exact crate name used
    Affected if The crate is present with a version lower than 0.4.4
  2. Identify the compilation target
    Check your .cargo/config.toml, build scripts, or CI configuration for the target triple. Common thumbv6m targets include thumbv6m-none-eabi
    Affected if The target is thumbv6m-none-eabi (ARM Cortex M0, M0+, M1)
  3. Verify the installed CMOV library version
    Run 'cargo tree -p <cmov-crate-name>' to see the exact version of the CMOV library being used, or inspect the version line in Cargo.lock
    Affected if The version is less than 0.4.4
  4. Confirm cryptographic code uses the CMOV crate
    Search your source code for imports from the CMOV crate (for example: 'use cmov::' or 'use rust_crypto_cmov::') and verify that conditional move operations are being called in cryptographic code
    Affected if Cryptographic operations import and use the CMOV crate for constant-time operations

You are affected if your project uses the RustCrypto CMOV library version below 0.4.4 while compiling for thumbv6m-none-eabi targets and employs the portable cmovnz implementation in cryptographic code.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 0.4.4 or later
Fixed in 0.4.4
Vendor patch github.com →
Interim mitigation

Upgrade the rust-crypto-cmov dependency to version 0.4.4 or later. Reassess any cryptographic code deployed to ARM Cortex-M0/M0+/M1 devices that previously used this library to confirm the constant-time property is restored.

Recommended fix High confidence

0.4.4

  1. Identify the rust-cmov or rustcrypto/utils crate in your project's Cargo.toml dependencies
  2. Update the crate version to 0.4.4 (e.g., cmov = "0.4.4" or rustcrypto/utils with the appropriate cmov feature)
  3. Run `cargo update` to fetch the new version
  4. Run `cargo build` or `cargo test` to verify the upgrade compiles and tests pass
  5. If using thumbv6m-none-eabi target for Cortex M0/M0+/M1, verify the constant-time behavior is now correct in the compiled output

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Cmov Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing4.0 h
  • Review / QA1.0 h
9.0 hours of engineering $1,540
Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-23519 in production — separate from our analysis above.

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What this is

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What belongs here
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  • Version or environment caveats, and links to real fixes
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