---
id: "CVE-2026-114114"
kind: "vulnerability"
aliases: ["CVE-2026-114114"]
title: "Vyper compiler: multi-byte characters can silently alter compiled numeric constants"
severity: "medium"
cvss: 6.0
epss: 0.00183
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["package", "python", "smart-contracts", "vyper"]
not_affected_if: ["ascii-only-source", "trusted-source-only"]
published_at: "2026-10-21T01:17:37+00:00"
first_seen_at: "2026-10-23T21:57:28+00:00"
updated_at: "2026-10-25T04:05:33+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-114114", "first_seen_at": "2026-10-23T21:57:28+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-114114", "first_seen_at": "2026-10-24T13:15:54+00:00"}]
---

# Vyper compiler: multi-byte characters can silently alter compiled numeric constants

Vyper mixes character offsets with UTF-8 byte offsets when rebuilding numeric literals, so non-ASCII source can shift the slices it reads. An attacker who supplies such source can get addresses, integers or other constants silently replaced in the compiled bytecode.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Run `vyper --version` and check whether it is below `0.1.0b12`, `0.1.0b14`, or in the range `0.4.1` to `0.5.0b1`
- Look for Vyper in `requirements.txt`, `pyproject.toml` or `poetry.lock` and check the pinned version
- Review whether any contract source you compile comes from outside your team and contains non-ASCII identifiers or a byte-order mark

## Fix

- Upgrade the Vyper package to a version at or past `0.1.0b12` for the 0.1.0b line, `0.1.0b14`, or `0.5.0b2` or later for the 0.5 line (exact patched release unknown from sources)
- Recompile and diff deployed bytecode against source for contracts built with an affected version

## Timeline

- 2026-10-23T21:57:28+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-114114
- 2026-10-24T13:15:54+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-114114

## From the sources

Vyper 0.1.0b1 before 0.1.0b12, 0.1.0b14, and 0.4.1 through 0.5.0b1 mix character-based line offsets with Python's UTF-8 byte col_offset values in vyper/ast/parse.py, so multi-byte characters shift the source slices used to reconstruct later numeric literals. An attacker contributing source with non-ASCII identifiers that NFKC-normalize to ASCII, or an invisible byte-order mark, can silently substitute addresses, integers or other constants in compiled code.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_