How severe is CVE-2026-53720?

No CVSS score has been assigned to CVE-2026-53720 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-53720?

CVE-2026-53720 affects the following packages: pymonocypher (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2026-53720?

Update pymonocypher to 4.0.2.8 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-53720 is resolved across your whole dependency graph.

How do I detect CVE-2026-53720 in my PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for pymonocypher, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-53720 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2026-53720 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-53720 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-53720?

CVE-2026-53720 has an EPSS (Exploit Prediction Scoring System) score of 0.2%, placing it in the 7th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-53720?

CVE-2026-53720 is classified as CWE-122 (CWE-122), Out-of-bounds Write (CWE-787), CWE-1284 (CWE-1284). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-53720 published, and has it been updated?

CVE-2026-53720 was published on September 3, 2026 and was last updated on October 21, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍 PyPI

Not in CISA KEV

CVE-2026-53720 — pymonocypher

Fix: jetperch/pymonocypher@90ff5b1

CVE-2026-53720 is a CWE-122 vulnerability in pymonocypher. A fix is available for pymonocypher — see the affected versions and patch details below.

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

Also known asGHSA-8f95-v3jq-cj86PYSEC-2026-3000

Published

Sep 3, 2026

Updated

Oct 21, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 22, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-53720.

EPSS Exploitation Probability

via FIRST.org ↗

0.2%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs7th percentile — riskier than 7% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

🐍pymonocypher

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

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.

Workarounds

Provide a correctly sized nb_blocks buffer.

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

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`pymonocypher`	all versions	4.0.2.8`pip install --upgrade 'pymonocypher==4.0.2.8'`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for pymonocypher, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update pymonocypher to 4.0.2.8 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-53720 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Frequently Asked Questions

### 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.

O3 Security · Impact-Aware SCA

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