CVE-2026-53720
pymonocypher: Potential heap buffer overflow on nb_blocks in argon2i_32 when provided buffer is too small
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.
Attack profile
How easy it is to exploit
- Attack vector
- Local
- Complexity
- Low
- Privileges needed
- None
- User interaction
- None
What an attacker can affect
- Confidentiality
- None
- Integrity
- Low
- Availability
- Low
Exploit likelihood
What each source reports
CVE List Score used
pymonocypher: Potential heap buffer overflow on nb_blocks in argon2i_32 when provided buffer is too small
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.
- Record
CVE-2026-53720- CVSS 4.0
- 5.1 Medium
CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N - Weakness
- CWE-122, CWE-787, CWE-1284
- Updated
- 2026-11-02
EUVDEUVD-2026-70531
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.
- Record
EUVD-2026-70531- CVSS 4.0
- 5.1 Medium
CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N - Updated
- 2026-11-02
GitHub AdvisoriesGHSA-8f95-v3jq-cj86
pymonocypher: Potential heap buffer overflow on nb_blocks in argon2i_32 when provided buffer is too small
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.
- Record
GHSA-8f95-v3jq-cj86- CVSS 4.0
- 5.1 Medium
CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N - Weakness
- CWE-122, CWE-787, CWE-1284
- Updated
- 2026-11-02
NVD
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.
- Record
CVE-2026-53720- CVSS 4.0
- 5.1 Medium
CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X - Weakness
- CWE-122, CWE-787, CWE-1284
- Updated
- 2026-11-02
OSV
pymonocypher: Potential heap buffer overflow on nb_blocks in argon2i_32 when provided buffer is too small
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.
- Record
CVE-2026-53720- CVSS 4.0
- 5.1 Medium
CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N - Weakness
- CWE-122, CWE-1284, CWE-787
- Updated
- 2026-11-02
OSVGHSA-8f95-v3jq-cj86
pymonocypher: Potential heap buffer overflow on nb_blocks in argon2i_32 when provided buffer is too small
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.
- Record
GHSA-8f95-v3jq-cj86- CVSS 4.0
- 5.1 Medium
CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N - Weakness
- CWE-122, CWE-1284, CWE-787
- Updated
- 2026-11-02
OSVPYSEC-2026-3000
pymonocypher: Potential heap buffer overflow on nb_blocks in argon2i_32 when provided buffer is too small
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.
- Record
PYSEC-2026-3000- CVSS 4.0
- 5.1 Medium
CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N - Updated
- 2026-11-02
Affected products
Affected packages
| Package | Affected | Fixed |
|---|---|---|
pymonocypherPyPI |
before 4.0.2.8 | 4.0.2.8 |
pymonocypherPyPI |
before 4.0.2.8, plus listed versions 0.1.10.1.20.1.30.1.43.1.0.0 Show 14 moreShow less3.1.3.03.1.3.13.1.3.23.1.3.33.1.3.43.1.3.53.1.3.64.0.2.14.0.2.24.0.2.34.0.2.44.0.2.54.0.2.64.0.2.7 |
4.0.2.8 |
History
| Recorded | Changed | Sources |
|---|---|---|
| first indexed | CVE List, EUVD, GitHub Advisories, NVD, OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2026-53720 is a medium vulnerability (CVSS 5.1) in Jetperch Pymonocypher, published July 9, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.18%, the 7th percentile. Fixed in pymonocypher 4.0.2.8.
References
github.com/jetperch/pymonocypher/security/advisories/GHSA-8f95-v3jq-cj86
nvd.nist.gov/vuln/detail/CVE-2026-53720
pypi.org/project/pymonocypher