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Medium

Cipher.update_into can corrupt memory if passed an immutable python object as the outbuf

  • Disclosed: 07.02.2023
  • Updated: 11.10.2026 15:17

Previously, Cipher.update_into would accept Python objects which implement the buffer protocol, but provide only immutable buffers:

pycon
>>> 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 software

Click a technology to see all vulnerabilities affecting it.

PlatformPackageVulnerable versionsFixed in
Python (PyPI) cryptography >= 1.8, < 39.0.1 39.0.1

References

CVSS score 6.5/10
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
Weakness (CWE)
CWE-754
Platform
Python (PyPI)
Package
cryptography
Disclosed
07.02.2023
Updated
11.10.2026 15:17

Sources and licenses

OSV / GitHub Advisory Database - PYSEC-2023-11 - PyPA Advisory Database; CC BY 4.0

OSV / GitHub Advisory Database - GHSA-w7pp-m8wf-vj6r - CC BY 4.0

Vulnerability history: cryptography

All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (24) in the archive
Total entries
24
First → latest
03.2017 08.2026
Without a fix
0
Exploited in attacks
0

Severity breakdown

  • High 12
  • Medium 7
  • Low 5

Disclosures per year

Severity:
  1. python-cryptography: Duplicate self-signed intermediates can cause exponential path-building
    High CVE-2026-69249 >= 42.0.0, < 49.0.0 49.0.0
  2. cryptography: PKCS#7 EnvelopedData decryption exposes a Bleichenbacher oracle through distinguishable errors and timing
    High CVE-2026-69247 >= 44.0.0, < 50.0.0 50.0.0
  3. Vulnerable OpenSSL included in cryptography wheels
    High · 7.5 ghsa-537c-gmf6-5ccf >= 0.5.0, < 48.0.1 48.0.1
  4. cryptography Vulnerable to a Subgroup Attack Due to Missing Subgroup Validation for SECT Curves
    High CVE-2026-26007 < 46.0.5 46.0.5
  5. cryptography NULL pointer dereference with pkcs12.serialize_key_and_certificates when called with a non-matching certificate and private key and an hmac_hash override
    High · 7.5 CVE-2024-26130 >= 38.0.0, < 42.0.4 42.0.4
  6. Python Cryptography package vulnerable to Bleichenbacher timing oracle attack
    High · 7.5 CVE-2023-50782 < 42.0.0 42.0.0
  7. cryptography mishandles SSH certificates
    High · 7.5 CVE-2023-38325 >= 40.0.0, < 41.0.2 41.0.2
  8. Vulnerable OpenSSL included in cryptography wheels
    High · 7.4 CVE-2023-0286 >= 0.8.1, < 39.0.1 39.0.1
  9. Cipher.update_into can corrupt memory if passed an immutable python object as the outbuf this entry
    Medium · 6.5 CVE-2023-23931 >= 1.8, < 39.0.1 39.0.1
  10. PyCA Cryptography symmetrically encrypting large values can lead to integer overflow
    High · 9.1 CVE-2020-36242 >= 3.1, < 3.3.2 3.3.2
  11. RSA decryption vulnerable to Bleichenbacher timing vulnerability
    High · 5.9 CVE-2020-25659 < 3.2 3.2
  12. PyCA Cryptography vulnerable to GCM tag forgery
    High · 7.5 CVE-2018-10903 >= 1.9.0, < 2.3 2.3
  13. Improper input validation in cryptography
    High · 7.5 CVE-2016-9243 < 1.5.3 1.5.3

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