pymonocypher: Potential heap buffer overflow on nb_blocks in argon2i_32 when provided buffer is too small (CVE-2026-53720) | HOL Guard CVE

Medium · CVSS 5.1CVE-2026-53720GHSA-8F95-V3JQ-CJ86

pymonocypher: Potential heap buffer overflow on nb_blocks in argon2i_32 when provided buffer is too small

Answer in brief

CVE-2026-53720 records a Medium severity (CVSS 5.1) vulnerability in pymonocypher: Potential heap buffer overflow on nb_blocks in argon2i_32 when provided buffer is too small. The current sources do not mark it as known exploited. The current feed maps jetperch/pymonocypher (generic), pymonocypher (pip). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 3, 2026Updated Sep 9, 2026Source checked Sep 17, 2026First seen by HOL Jul 9, 2026Material review Sep 9, 2026

Upstream Advisory

Key facts

Risk: Medium · CVSS 5.1
Exploitation: Not marked as known exploited
Affected software: 2 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 5.1. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps jetperch/pymonocypher (generic), pymonocypher (pip). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
jetperch/pymonocyphergeneric	< 4.0.2.8	Not reported
pymonocypherpip	<4.0.2.8	4.0.2.8

Recommended response

Check inventory. Check lockfiles and deployed manifests for jetperch/pymonocypher, pymonocypher.
Review the reported fix. Update pymonocypher to 4.0.2.8 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Sep 3, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 9, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Jul 9, 2026

Sources and claim methodology

Upstream source description

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.

Quoted source text, attributed separately from HOL analysis.