CVE-2026-23519 RustCrypto cmov: thumbv6m-none-eabi compiler emits non-constant time assembly when using cmovnz
Attackers can exploit timing side-channels in RustCrypto cmov on Cortex-M0/M1 targets to potentially recover sensitive cryptographic data.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-23519?
CVE-2026-23519 is a high-severity vulnerability in RustCrypto utils, published on 15 Jan 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Which versions are affected by CVE-2026-23519?
4 open source packages ship an affected version, including ctutils and cmov. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
ctutils crates.io | From 0.0.0-0 | 0.4.4 |
cmov crates.io | All versions | 0.4.4 |
cmov crates.io | All versions | 0.4.4 |
cmov crates.io | From 0.0.0-0 | 0.4.4 |
Products include Rustcrypto Cmov.
How do I fix CVE-2026-23519?
Upgrade ctutils to 0.4.4 or later.
Is CVE-2026-23519 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-23519 exists.
Other vulnerabilities in RustCrypto utils
Sources
Also known as GHSA-2gqc-6j2q-83qp, RUSTSEC-2026-0003, RUSTSEC-2026-0385.