HKDF in cryptography before 1.5.2 returns an empty byte-string if used with a length less than algorithm.digest_size.
Priority LOW 39CWE-20Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- —
- Confidentiality · integrity · availability
- None · High · None
- Fix status
- Partial Red Hat: 4 without a fix
Attack profile from CVSS 3.1 · NVD. Fix status from CNA, GitHub and Red Hat.
Summary
HKDF in cryptography before 1.5.2 returns an empty byte-string if used with a length less than algorithm.digest_size.
Why it matters now
EPSS 0.03464 89th percentileScored 2026-11-07
Fix Partial cryptography (PyPI): 1.5.3Red Hat: 4 without a fix
SSVC decision points
Not available: CISA has not published SSVC decision points for this record.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| — | — | all versions | — | No fix listed | CNA |
| — | cryptography (PyPI) | before 1.5.3 | 1.5.3 | Patch available | GHSA-q3cj-2r34-2cwc |
- — Vendor— Affected all versions Fixed in — No fix listed CNA
- cryptography (PyPI) Vendor— Affected before 1.5.3 Fixed in 1.5.3 Patch available GHSA-q3cj-2r34-2cwc
CPE configurations NVD · 6
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:cryptography.io:cryptography:*:*:*:*:*:python:*:* | up to 1.5.2 | Vulnerable | Cryptography.io |
| cpe:2.3:o:fedoraproject:fedora:23:*:*:*:*:*:*:* | 23 | Vulnerable | Fedoraproject |
| cpe:2.3:o:fedoraproject:fedora:24:*:*:*:*:*:*:* | 24 | Vulnerable | Fedoraproject |
| cpe:2.3:o:fedoraproject:fedora:25:*:*:*:*:*:*:* | 25 | Vulnerable | Fedoraproject |
| cpe:2.3:o:canonical:ubuntu_linux:16.04:*:*:*:lts:*:*:* | 16.04 | Vulnerable | Canonical |
| cpe:2.3:o:canonical:ubuntu_linux:16.10:*:*:*:*:*:*:* | 16.10 | Vulnerable | Canonical |
- cpe:2.3:a:cryptography.io:cryptography:*:*:*:*:*:python:*:* Versions up to 1.5.2 Vulnerable ·Cryptography.io
- cpe:2.3:o:fedoraproject:fedora:23:*:*:*:*:*:*:* Versions 23 Vulnerable ·Fedoraproject
- cpe:2.3:o:fedoraproject:fedora:24:*:*:*:*:*:*:* Versions 24 Vulnerable ·Fedoraproject
- cpe:2.3:o:fedoraproject:fedora:25:*:*:*:*:*:*:* Versions 25 Vulnerable ·Fedoraproject
- cpe:2.3:o:canonical:ubuntu_linux:16.04:*:*:*:lts:*:*:* Versions 16.04 Vulnerable ·Canonical
- cpe:2.3:o:canonical:ubuntu_linux:16.10:*:*:*:*:*:*:* Versions 16.10 Vulnerable ·Canonical
Remediation
- Fix · GHSA-q3cj-2r34-2cwc cryptography (PyPI) Fixed in 1.5.3 Advisory →
Vendor assessments
Red Hat
Red Hat rating: Low. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Enterprise Linux OpenStack Platform 7 (Kilo) | Affected | No fix planned: Will not fix |
| Red Hat OpenStack Platform 10 (Newton) | Affected | No fix planned: Will not fix |
| Red Hat OpenStack Platform 8 (Liberty) | Affected | No fix planned: Will not fix |
| Red Hat OpenStack Platform 9 (Mitaka) | Affected | No fix planned: Will not fix |
Not affected: 1 product
- Red Hat Enterprise Linux 7
Timeline
- 2026-10-02 Threatist record created from CVE-2016-9243
- 2026-10-03 Alias added: GHSA-q3cj-2r34-2cwc
References
Patch 2
Advisory 8
Other 9
- https://cryptography.io/en/latest/changelog/#v1-5-3
- https://github.com/pyca/cryptography
- https://github.com/pypa/advisory-database/tree/main/vulns/cryptography/PYSEC-2017-8.yaml
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/5R2ZOBMPWDFFHUZ6QOZZY36A6H5CGJXL
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/U23KDR2M2N7W2ZSREG63BVW7D4VC6CIZ
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WQ5G7KHKZC4SI23JE7277KZXM57GEQKT
- https://lists.fedoraproject.org/archives/list/[email protected]/message/5R2ZOBMPWDFFHUZ6QOZZY36A6H5CGJXL
- https://lists.fedoraproject.org/archives/list/[email protected]/message/U23KDR2M2N7W2ZSREG63BVW7D4VC6CIZ
- https://lists.fedoraproject.org/archives/list/[email protected]/message/WQ5G7KHKZC4SI23JE7277KZXM57GEQKT
Sources
- CVE-2016-9243 · CVE Program
- CVE-2016-9243 · NVD
- FIRST EPSS
- GHSA-q3cj-2r34-2cwc · GitHub Advisory Database · CC BY 4.0
- CVE-2016-9243 · Red Hat security data · CC BY 4.0
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