Summary
pymonocypher: Potential heap buffer overflow on nbblocks in argon2i32 when provided buffer is too small
Workarounds
Provide a correctly sized nb_blocks buffer.
pymonocypher thanks Haris (hextheshadow) for the vulnerability report, details, and recommended fix.
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.
A write operation targets a memory location beyond the intended buffer boundary. Typical impact: memory corruption, crash, or arbitrary code execution.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
Fixed in 4.0.2.8, which now verifies that nb_blocks is large enough. See 90ff5b1.
Frequently Asked Questions
- What is CVE-2026-53720? CVE-2026-53720 is a medium-severity out-of-bounds write vulnerability in pymonocypher (pip), affecting versions < 4.0.2.8. It is fixed in 4.0.2.8. A write operation targets a memory location beyond the intended buffer boundary.
- Which versions of pymonocypher are affected by CVE-2026-53720? pymonocypher (pip) versions < 4.0.2.8 is affected.
- Is there a fix for CVE-2026-53720? Yes. CVE-2026-53720 is fixed in 4.0.2.8. Upgrade to this version or later.
- Is CVE-2026-53720 exploitable, and should I be worried? Whether CVE-2026-53720 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-53720 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-53720? Upgrade
pymonocypherto 4.0.2.8 or later.