CVE-2026-23519
Rustcrypto Cmov ≤ 0.4.4
Raw vector
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:H/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:XSummary
CVE-2026-23519 is a high-severity Observable Timing Discrepancy (CWE-208) vulnerability in Rustcrypto Cmov. Its CVSS base score is 8.9 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Password Guessing (T1110.001); ranked at the 40th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified map to IA-6 (Authentication Feedback) and SA-11 (Developer Testing and Evaluation) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-23519 is a timing side-channel vulnerability in the RustCrypto CMOV crate, part of the RustCrypto/utils repository. The crate provides conditional move CPU intrinsics intended to execute in constant time on major platforms without compiler rewriting to branches. In versions prior to 0.4.4, when targeting thumbv6m-none-eabi (Cortex-M0, M0+, and M1 architectures), the compiler emits non-constant-time assembly for the portable cmovnz implementation. This violates the constant-time guarantee, mapped to CWE-208 (Observable Discrepancy) and CWE-203 (Observable Behavior), with a CVSS v3.1 base score of 9.8 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H).
Remote attackers require no privileges, authentication, or user interaction to exploit this over a network with low complexity. Exploitation involves observing timing differences in cmovnz operations, potentially allowing recovery of sensitive data such as cryptographic keys during operations relying on the crate for constant-time conditional moves. The high impact on confidentiality, integrity, and availability stems from the side-channel leakage enabling broader compromise of affected embedded systems using these targets.
The GitHub security advisory (GHSA-2gqc-6j2q-83qp) and commit 55977257e7c82a309d5e8abfdd380a774f0f9778 detail the fix in version 0.4.4, which addresses the compiler-emitted assembly issue for thumbv6m-none-eabi targets. Security practitioners should update to RustCrypto/utils 0.4.4 or later and audit dependencies using vulnerable versions in Cortex-M0/M0+/M1 firmware.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-2731
Vulnerability Data
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…
more
assembly when using cmovnz (portable version). This vulnerability is fixed in 0.4.4.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
—
—
- 1 hardening rule · 1 OS baseline
V11.2.4
Mitigating Controls (NIST 800-53 r5) AI
Obscures authentication feedback so that success/failure differences are not observable to attackers.
Developer testing can include timing analysis or side-channel test cases that reveal observable timing discrepancies.
Requires error messages to avoid revealing exploitable details, directly stopping observable response discrepancies.
Engineering principles can mandate constant-time algorithms and side-channel resistance so timing discrepancies are never introduced.
Requiring approved cryptographic modules and algorithms implicitly demands implementations free of observable timing leaks.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure SDLC practices directly require constant-time implementations that eliminate observable timing discrepancies.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Consistent reference clocks limit the attacker's ability to measure or manipulate timing differences that could reveal internal state or processing paths.