CVE-2016-9243

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

Published: 2017-03-27 Last update: 2026-05-13 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2016-9243 is rated Moderate Risk (58.4/100): CVSS High severity, with medium exploitation likelihood (EPSS 1.65%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2016-9243

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2025-06-19 1.64% 1.65% +0.01%
2 2025-03-30 3.97% 1.64% -2.33%
3 2025-03-29 — 3.97% —

Full EPSS history (10 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2016-9243

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 3.6 [email protected]
5.0 2.0 MEDIUM
AV:N/AC:L/Au:N/C:N/I:P/A:N Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:N)
No availability impact.
 10.0 2.9 [email protected]

Weakness enumeration for CVE-2016-9243

GitHub Security Advisory for CVE-2016-9243

GHSA-q3cj-2r34-2cwc · Severity: high · Ecosystem: pip — Improper input validation in cryptography

OS Trackers for CVE-2016-9243

vendor priority summary link
debian not yet assigned CVE-2016-9243 not yet assigned priority: Debian including 1 source packages (python-cryptography), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2016-9243
redhat low — https://access.redhat.com/security/cve/CVE-2016-9243
ubuntu medium CVE-2016-9243 medium priority: Ubuntu including 1 source packages (python-cryptography), 5 status rows across 5 suites (precise, trusty, upstream, xenial, yakkety): released 3, DNE 2. https://ubuntu.com/security/CVE-2016-9243

Affected software / configurations for CVE-2016-9243

Vendor Product Version Raw CPE
cryptography.io cryptography <= 1.5.2 cpe:2.3:a:cryptography.io:cryptography:*:*:*:*:*:python:*:*
fedoraproject fedora 23 cpe:2.3:o:fedoraproject:fedora:23:*:*:*:*:*:*:*
fedoraproject fedora 24 cpe:2.3:o:fedoraproject:fedora:24:*:*:*:*:*:*:*
fedoraproject fedora 25 cpe:2.3:o:fedoraproject:fedora:25:*:*:*:*:*:*:*
canonical ubuntu_linux 16.04 cpe:2.3:o:canonical:ubuntu_linux:16.04:*:*:*:lts:*:*:*
canonical ubuntu_linux 16.10 cpe:2.3:o:canonical:ubuntu_linux:16.10:*:*:*:*:*:*:*

References for CVE-2016-9243

URL Tags
http://www.openwall.com/lists/oss-security/2016/11/09/2 Mailing List Patch VDB Entry
http://www.securityfocus.com/bid/94216 Broken Link Third Party Advisory VDB Entry
http://www.ubuntu.com/usn/USN-3138-1 Third Party Advisory
https://cryptography.io/en/latest/changelog Release Notes Third Party Advisory
https://github.com/pyca/cryptography/commit/b924696b2e8731f39696584d12cceeb3aeb2d874 Patch Third Party Advisory
https://github.com/pyca/cryptography/issues/3211 Issue Tracking Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/5R2ZOBMPWDFFHUZ6QOZZY36A6H5CGJXL/ Mailing List Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/U23KDR2M2N7W2ZSREG63BVW7D4VC6CIZ/ Mailing List Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/WQ5G7KHKZC4SI23JE7277KZXM57GEQKT/ Mailing List Third Party Advisory
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