---
id: CVE-2026-53720
title: pymonocypher uses cython to wrap the Monocypher C library
summary: >-
  pymonocypher uses cython to wrap the Monocypher C library. Prior to version
  4.0.2.8, the argon2i_32 implementation does not check the nb_blocks size. If
  the caller does not provide a sufficiently large buffer based on the API
  contract, t…
severity: medium
cwe:
  - CWE-122
  - CWE-787
  - CWE-1284
vendor: pymonocypher
product: pymonocypher
affected:
  - pymonocypher < 4.0.2.8
patched:
  - pymonocypher 4.0.2.8
published: '2026-09-03'
updated: '2026-09-09'
sourceUpdated: '2026-09-09T21:09:13.080'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-53720'
references:
  - url: >-
      https://github.com/jetperch/pymonocypher/commit/90ff5b13b13b5673c372e188f482d8c172e6ab86
    label: security-advisories@github.com
  - url: 'https://github.com/jetperch/pymonocypher/releases/tag/v4.0.2.8'
    label: security-advisories@github.com
  - url: >-
      https://github.com/jetperch/pymonocypher/security/advisories/GHSA-8f95-v3jq-cj86
    label: security-advisories@github.com
  - url: 'https://github.com/advisories/GHSA-8f95-v3jq-cj86'
tags:
  - nvd
  - ghsa
  - pip
epss: 0.00178
epssPercentile: 0.06564
aliases:
  - GHSA-8f95-v3jq-cj86
ecosystem: pip
ingestedAt: '2026-07-09T13:51:05.178Z'
---

## Overview

pymonocypher uses cython to wrap the Monocypher C library. Prior to version 4.0.2.8, the argon2i_32 implementation does not check the nb_blocks size. If the caller does not provide a sufficiently large buffer based on the API contract, then argon2i_32 will write past the end of the buffer and possibly corrupt the heap. This issue has been patched in version 4.0.2.8.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Package advisory (CVE-2026-53720)

Affected packages:

- `pymonocypher < 4.0.2.8`

Patched in:

- `pymonocypher 4.0.2.8`

Source: https://github.com/advisories/GHSA-8f95-v3jq-cj86