CVE-2026-53720 — pymonocypher: Potential heap buffer overflow on nb_blocks in argon2i_32 when provided buffer is too small

Affected: jetperch pymonocypher

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.

GHSA-8f95-v3jq-cj86 — pymonocypher: Potential heap buffer overflow on nb_blocks in argon2i_32 when provided buffer is too small

Affected: PyPI: pymonocypher

### Impact 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.

### Patches Fixed in 4.0.2.8, which now verifies that nb_blocks is large enough. See [90ff5b1](https://github.com/jetperch/pymonocypher/commit/90ff5b13b13b5673c372e188f482d8c172e6ab86).

### Workarounds Provide a correctly sized nb_blocks buffer.

pymonocypher thanks Haris (hextheshadow) for the vulnerability report, details, and recommended fix.

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CVE-2026-53720 — pymonocypher: Potential heap buffer overflow on nb_blocks in argon2i_32 when provided buffer is too small

GHSA-8f95-v3jq-cj86 — pymonocypher: Potential heap buffer overflow on nb_blocks in argon2i_32 when provided buffer is too small