CVE-2023-23931 is a medium-severity (CVSS 4.8) CWE-754 vulnerability in cryptography. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for cryptography — see the affected versions and patch details below.
Cipher.update_into can corrupt memory in pyca cryptography
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for CVE-2023-23931.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
cryptographyReal-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
Previously, Cipher.update_into would accept Python objects which implement the buffer protocol, but provide only immutable buffers:
>>> outbuf = b"\x00" * 32
>>> c = ciphers.Cipher(AES(b"\x00" * 32), modes.ECB()).encryptor()
>>> c.update_into(b"\x00" * 16, outbuf)
16
>>> outbuf
b'\xdc\x95\xc0x\xa2@\x89\x89\xadH\xa2\x14\x92\x84 \x87\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'
This would allow immutable objects (such as bytes) to be mutated, thus violating fundamental rules of Python. This is a soundness bug -- it allows programmers to misuse an API, it cannot be exploited by attacker controlled data alone.
This now correctly raises an exception.
This issue has been present since update_into was originally introduced in cryptography 1.8.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | cryptography | ≥ 1.8&&< 39.0.1 | 39.0.1pip install --upgrade 'cryptography==39.0.1' |
Affected Products
cryptographycryptography.ioResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for cryptography, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update cryptography to 39.0.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-23931 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Ansible Automation Platform 2.4 for RHEL 8 | python3x-cryptography-0:38.0.4-2.el8ap | RHSA-2023:4693 |
| Red Hat Ansible Automation Platform 2.4 for RHEL 8 | automation-controller-0:4.4.3-1.el8ap | RHSA-2023:4971 |
| Red Hat Enterprise Linux 8 | python39:3.9-8100020240214182535.7044f6c1 | RHSA-2024:2985 |
| Red Hat Enterprise Linux 8 | python-cryptography-0:3.2.1-6.el8 | RHSA-2023:7096 |
| Red Hat Enterprise Linux 9 | python-cryptography-0:36.0.1-4.el9 | RHSA-2023:6615 |
| Red Hat Quay 3 | quay/quay-rhel8:v3.10.0-150 | RHSA-2023:7341 |
| Red Hat Software Collections for Red Hat Enterprise Linux 7 | rh-python38-python-cryptography-0:2.8-6.el7 | RHSA-2023:6793 |
Frequently Asked Questions
Is CVE-2023-23931 in your dependencies?
Find it across PyPI, including transitive dependencies.