CVE-2016-9243

Improper input validation in cryptography

7.5 HighFix available

CVE-2016-9243 is a high vulnerability (CVSS 7.5) in Cryptography.io Cryptography, published November 9, 2016. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 3.46%, the 89th percentile. Fixed in cryptography 1.5.3.

HKDF in cryptography before 1.5.2 returns an empty byte-string if used with a length less than algorithm.digest_size.

Attack profile

How easy it is to exploit

Attack vector: Network
Complexity: Low
Privileges needed: None
User interaction: None

What an attacker can affect

Confidentiality: None
Integrity: High
Availability: None

Exploit likelihood

3.46%Up 1.9 points since Feb 4, 2022

What each source reports

NVD Score used 7.5

HKDF in cryptography before 1.5.2 returns an empty byte-string if used with a length less than algorithm.digest_size.

Record: CVE-2016-9243
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
CVSS 2.0: 5.0 MediumAV:N/AC:L/Au:N/C:N/I:P/A:N
Updated: 2026-11-02

CVE List No score

HKDF in cryptography before 1.5.2 returns an empty byte-string if used with a length less than algorithm.digest_size.

Record: CVE-2016-9243
Updated: 2026-11-02

EUVDEUVD-2017-0020 No score

HKDF in cryptography before 1.5.2 returns an empty byte-string if used with a length less than algorithm.digest_size.

Record: EUVD-2017-0020
Updated: 2026-11-03

GitHub AdvisoriesGHSA-q3cj-2r34-2cwc 8.7

Improper input validation in cryptography

HKDF in cryptography before 1.5.3 returns an empty byte-string if used with a length less than algorithm.digest_size.

Record: GHSA-q3cj-2r34-2cwc
CVSS 4.0: 8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
CVSS 3.0: 7.5 HighCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Weakness: CWE-20
Updated: 2026-11-02

OSVBELL-CVE-2016-9243 7.5

CVE-2016-9243 does not affect BellSoft software

Record: BELL-CVE-2016-9243
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Updated: 2026-11-02

OSV 7.5

HKDF in cryptography before 1.5.2 returns an empty byte-string if used with a length less than algorithm.digest_size.

Record: CVE-2016-9243
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Updated: 2026-11-02

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OSVDEBIAN-CVE-2016-9243 7.5

HKDF in cryptography before 1.5.2 returns an empty byte-string if used with a length less than algorithm.digest_size.

Record: DEBIAN-CVE-2016-9243
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Updated: 2026-11-02

OSVGHSA-q3cj-2r34-2cwc 8.7

Improper input validation in cryptography

HKDF in cryptography before 1.5.3 returns an empty byte-string if used with a length less than algorithm.digest_size.

Record: GHSA-q3cj-2r34-2cwc
CVSS 4.0: 8.7 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
CVSS 3.0: 7.5 HighCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Weakness: CWE-20
Updated: 2026-11-02

OSVUBUNTU-CVE-2016-9243 7.5

HKDF in cryptography before 1.5.2 returns an empty byte-string if used with a length less than algorithm.digest_size.

Record: UBUNTU-CVE-2016-9243
CVSS 3.1: 7.5 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
CVSS 3.0: 7.5 HighCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Updated: 2026-11-02

OSVMGASA-2016-0377 No score

Updated python-cryptography package fixes security vulnerability

Fixed a bug where HKDF would return an empty byte-string if used with a length less than algorithm.digest_size. (CVE-2016-9243)

Record: MGASA-2016-0377
Updated: 2026-11-02

OSVPYSEC-2017-8 No score

HKDF in cryptography before 1.5.2 returns an empty byte-string if used with a length less than algorithm.digest_size.

Record: PYSEC-2017-8
Updated: 2026-11-02

OSVUSN-3138-1 No score

python-cryptography vulnerability

Markus Döring discovered that python-cryptography incorrectly handled certain HKDF lengths. This could result in python-cryptography returning an empty string instead of the expected derived key.

Record: USN-3138-1
Updated: 2026-11-02

Affected products

Affected packages

Affected packages
Package	Affected	Fixed
`cryptography` PyPI	before 1.5.3	1.5.3
`python-cryptography` Debian:12	before 1.5.3-1	1.5.3-1
`python-cryptography` Debian:13	before 1.5.3-1	1.5.3-1
`python-cryptography` Debian:14	before 1.5.3-1	1.5.3-1
`cryptography` PyPI	before 1.5.3, plus listed versions 0.10.20.2.10.2.20.3 Show 37 moreShow less 0.40.50.5.10.5.20.5.30.5.40.60.6.10.70.7.10.7.20.80.8.10.8.20.90.9.10.9.20.9.31.01.0.11.0.21.11.1.11.1.21.21.2.11.2.21.2.31.31.3.11.3.21.3.31.3.41.41.51.5.11.5.2	1.5.3
`python-cryptography` Mageia:5	before 1.0.2-1.1.mga5	1.0.2-1.1.mga5
`python-cryptography` Ubuntu:16.04:LTS	before 1.2.3-1ubuntu0.1, plus listed versions 1.0.1-1ubuntu11.0.2-11.1-11.1.1-11.1.1-1ubuntu1 Show 4 moreShow less 1.1.1-1ubuntu21.1.1-1ubuntu31.2.2-21.2.3-1	1.2.3-1ubuntu0.1

History

History
When	Changed	Sources
2026-11-03	aliases	EUVD
2026-11-02	created	CVE List, GitHub Advisories, NVD, OSV

References

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