CVE-2016-5699
MEDIUMEPSS 95th pctlDescription
CRLF injection vulnerability in the HTTPConnection.putheader function in urllib2 and urllib in CPython (aka Python) before 2.7.10 and 3.x before 3.4.4 allows remote attackers to inject arbitrary HTTP headers via CRLF sequences in a URL.
How to fix
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Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Exploit Intelligence
Very high risk: more likely to be exploited than 95% of all known CVEs.
References
Related Vulnerabilities
Other CWE-113 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2022-37436 | Medium | 5.3 | 61% | - | Fix |
| CVE-2024-52875 | High | 8.8 | 30% | - | - |
| CVE-2016-8024 | High | 8.1 | 8.7% | - | - |
| CVE-2017-17742 | Medium | 5.3 | 5.5% | - | Fix |
| CVE-2016-5325 | Medium | 6.1 | 4.1% | - | Fix |
| CVE-2018-16979 | Medium | 6.1 | 3.0% | - | - |
Common questions
How do I fix CVE-2016-5699?
Published advisories record a fix for 16 affected products. The "How to fix" section on this page lists the fixed version and source advisory for each one, so apply the entry matching what you actually run.
Is CVE-2016-5699 being actively exploited?
Not that we know of. CVE-2016-5699 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 9.9% is the estimated probability that it will be exploited in the next 30 days. That is higher than 95% of all scored CVEs.
How severe is CVE-2016-5699?
CVE-2016-5699 has a CVSS v3 base score of 6.1, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2016-5699 affect?
Published advisories record a fix for python2.7 (Debian), libpython2.7 (Ubuntu), libpython2.7-minimal (Ubuntu), libpython2.7-stdlib (Ubuntu), and 12 more. Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-06-17.