What is CVE-2016-5421?

CVE-2016-5421 is a high-severity vulnerability in Haxx Libcurl, classified under Use After Free. CVSS score: 8.1/10. Published 2016-08-10.

How severe is CVE-2016-5421?

High severity. CVSS v3 base score is 8.1 out of 10.

Is CVE-2016-5421 known to be exploited?

1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Use After Free in Haxx Libcurl

CVE-2016-5421

Use-after-free vulnerability in libcurl before 7.50.1 allows attackers to control which connection is used or possibly have unspecified other impact via unknown vectors.

Vulnerability class: Use-After-Free

Published 2016-08-10 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 8.1 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.080 (94.7th percentile), scored 2026-10-18.

Low probability of exploitation in the next 30 days, but still tracked. 95th percentile — 94.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.080 · newest: 0.080 · change: 0.000

Affected products

Haxx Libcurl
Canonical Ubuntu Linux — versions 12.04, 14.04, 16.04
Debian Linux — versions 8.0
Fedoraproject Fedora — versions 23, 24
openSUSE Leap — versions 42.1
openSUSE — versions 13.2

Weakness classification (CWE)

CWE-416 — Use After Free

Public proof-of-concept exploits

marklogic/marklogic-docker

References

access.redhat.com/errata/RHSA-2018:3558 (vendor-advisory, Third Party Advisory)
source.android.com/security/bulletin/2016-12-01.html (Third Party Advisory)
www.slackware.com/security/viewer.php (vendor-advisory, Third Party Advisory)
www.securityfocus.com/bid/92306 (VDB Entry, Third Party Advisory, vdb-entry)
www.debian.org/security/2016/dsa-3638 (vendor-advisory, Third Party Advisory)
curl.haxx.se/docs/adv_20160803C.html (Mitigation, Vendor Advisory)
lists.opensuse.org/opensuse-updates/2016-09/msg00011.html (vendor-advisory, Third Party Advisory)
www.tenable.com/security/tns-2016-18 (Third Party Advisory)
lists.opensuse.org/opensuse-updates/2016-09/msg00094.html (vendor-advisory, Third Party Advisory)
www.securitytracker.com/id/1036536 (VDB Entry, Third Party Advisory, vdb-entry)

Frequently asked questions

What is CVE-2016-5421?: CVE-2016-5421 is a high-severity vulnerability in Haxx Libcurl, classified under Use After Free. CVSS score: 8.1/10. Published 2016-08-10.
How severe is CVE-2016-5421?: High severity. CVSS v3 base score is 8.1 out of 10.
Is CVE-2016-5421 known to be exploited?: 1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.