Vyper EUVD-2026-106919

Exploitation requires that a victim compile attacker-supplied Vyper source with an affected version (0.1.0b1 before 0.1.0b17, or 0.4.1 through 0.5.0b1) that contains line-separator characters Python's str.splitlines() treats as line breaks (e.g. form feed U+000C, U+2028) hidden in comments, string contents, or indentation. The attack is limited by requiring a human workflow: the attacker must get source accepted/reviewed and the victim must compile it, and the discrepancy only affects numeric literal (address, integer, decimal) classification and validation - it does not grant remote system access. It relies on code reviewers failing to notice invisible Unicode characters in a diff; projects that render or normalize such characters, or compile only trusted first-party source, are not realistically exposed.

This is a medium-severity integrity flaw, not an urgent remote-code-execution priority. The vendor-supplied CVSS 4.0 vector (AV:N/AC:L/AT:P/PR:N/UI:P, VI:H only) scores 6.0 and correctly reflects an attack that depends on human workflow rather than direct remote compromise: no confidentiality or availability impact (VC:N/VA:N), and exploitation requires both an attack prerequisite (AT:P) and victim interaction (UI:P - someone must compile the malicious source). No EPSS score was provided, so statistical exploitation likelihood cannot be assessed. There is no CISA KEV listing and no public exploit was supplied in the intelligence, so this is 'no public exploit identified at time of analysis.' CWE-436 (interpretation conflict between Python's str.splitlines() and the actual parser) matches the description precisely. The real-world risk is concentrated and targeted: it matters most to teams that compile third-party or contributed Vyper source for on-chain deployment, where silently altered address/integer/decimal constants can redirect funds or change contract logic undetected. It is a genuine supply-chain/source-review concern for Vyper users but is not a candidate for mass automated exploitation. Note: the vector is CVSS 4.0, not 3.1, and PR:N here means no system privilege is needed - but the practical precondition is the ability to get source in front of a victim compiler.

An attacker submits a pull request or shares Vyper source containing invisible characters (form feed or U+2028) tucked into comments, strings, or indentation. Because an affected Vyper version builds its line table with str.splitlines() while the Python parser ignores those characters, numeric literals are validated against shifted source, so a maintainer who reviews and compiles the code deploys a contract whose address, integer, or decimal constants differ from what the diff appeared to show. No public exploit code was provided, but the technique is straightforward to reproduce once understood.